Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yasuyuki Takata Last modified date:2021.05.31

Professor / Thermal Engineering / Department of Mechanical Engineering / Faculty of Engineering


Papers
1. Biao Shen, Tomosuke Mine, Naoki Iwata, Sumitomo Hidaka, Koji Takahashi, Yasuyuki Takata, Deterioration of boiling heat transfer on biphilic surfaces under very low pressures, Experimental Thermal and Fluid Science, 10.1016/j.expthermflusci.2019.110026, 113, 2020.05, Surface wettability engineering has attracted growing attention in recent years as an effective tool to enhance boiling heat transfer. On wettability-patterned (so-called biphilic) surfaces in particular, subatmospheric boiling has been shown to be nearly free of the severe degradation of heat transfer rate that tends otherwise to prevail on plain surfaces. The surprisingly consistent performance under reduced-pressure conditions can be attributed to the rather strong pinning of the three-phase contact line (TPCL) at the border between the hydrophobic and hydrophilic surfaces, which essentially eliminates the waiting period between bubble cycles. Only when the pressure is decreased sufficiently low does the transition to the undesired mode of intermittent boiling eventually occur on the biphilic surface. The purpose of the present study is to investigate the physical mechanism for the heat transfer deterioration on a mixed-wettability surface at very low pressures. To that end, we performed high-speed visualization experiments of the process of bubble nucleation and growth on a smooth copper surface coated with a single hydrophobic polytetrafluoroethylene (PTFE) spot, under different surface superheats and system pressures. The results show an interesting correlation between the TPCL behavior and the bubble growth dynamics. Specifically, under some certain threshold of pressure, it would become increasingly likely for the TPCL to be dislodged from its pinned position on the biphilic surface under a particularly rapid bubble expansion. As a result, full flooding of the hydrophobic surface might ensue, which is deemed responsible for temporary deactivation of the hydrophobic spot as a viable nucleation site. Furthermore, based on the diffuse-interface simulations of TPCL propagation across heterogeneous wettabilities, a comparison of cases with different bubble expansion rates offered qualitative evidence supporting the critical role of such accelerated bubble growth rate in driving the TPCL to overcome the energy barrier raised at the wettability divide..
2. A. Widyaparaga, T. Hiromatsu, Deendarlianto, M. Kohno, Y. Takata, Acoustic field alteration in a 100 Hz dual acoustic driver straight tube travelling wave thermoacoustic heat pump for thermoacoustic heat transport control, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2019.119274, 151, 2020.04, A dual acoustic driver thermoacoustic heat pump was constructed to investigate the effect of acoustic field control on travelling wave thermoacoustic heat transport at a frequency of 100 Hz. The acoustic field was controlled by varying the phase difference and magnitude between the two drivers. Variation of phase difference demonstrated the change of both acoustic power flow direction and standing-travelling wave characteristics. Maximum temperature differences obtained between the ends of the regenerator were 23 °C and 19 °C when the acoustic power was flowing in the negative and positive directions, respectively. It has been shown that matching impedances on the cold and hot side of the regenerator influence the thermoacoustic heat pumping characteristics. Where monodirectional acoustic flow was observed on both sides of the regenerator, the impedance angles also coincided well. Variation of magnitude displayed a trend in which activation of an opposing acoustic driver at weaker power enhanced acoustic power flow and heat transport. A maximum temperature difference between the hot and cold sections of 23 °C is obtained when the input electric power of the opposing acoustic driver was 17% of the power of the initial acoustic driver where the impedances and impedance angles on both ends of the regenerator are matched but the acoustic field travelling wave characteristics are still sufficient for travelling wave device operation..
3. Biao Shen, Jiewei Liu, Gustav Amberg, Minh Do-Quang, Junichiro Shiomi, Koji Takahashi, Yasuyuki Takata, Contact-line behavior in boiling on a heterogeneous surface
Physical insights from diffuse-interface modeling, Physical Review Fluids, 10.1103/PhysRevFluids.5.033603, 5, 3, 2020.03, Enhancement of boiling heat transfer on biphilic (mixed-wettability) surfaces faces a sudden reversal at low pressures, which is brought about by excessive contact-line spreading across the wetting heterogeneities. We employ the diffuse-interface approach to numerically study bubble expansion on a heating surface that consists of opposing wettabilities. The results show a dramatic shift in the dynamics of a traversing contact line across the wettability divide under different gravities, which correspond to variable bubble growth rates. Specifically, it is found that the contact-line propagation tends to follow closely the rapidly expanding bubble at low gravity, with only a brief interruption at the border between the hydrophobic and hydrophilic sections of the surface. Only when the bubble growth becomes sufficiently weakened at high gravity does the contact line get slowed down drastically to the point of being nearly immobilized at the edge of the hydrophilic surface. The following bubble expansion, which faces strong limitations in the direction parallel to the surface, features a consistent apparent contact angle at around 66.4°, regardless of the wettability combination. A simple theoretical model based on the force-balance analysis is proposed to describe the physical mechanism behind such a dramatic transition in the contact-line behavior..
4. Zhenying Wang, Daniel Orejon, Khellil Sefiane, Yasuyuki Takata, Effect of substrate conductivity on the transient thermal transport of hygroscopic droplets during vapor absorption, Micromachines, 10.3390/mi11020193, 11, 2, 2020.02, In all kinds of liquid desiccant dehumidification systems, the temperature increase of the desiccant solution due to the effect of absorptive heating is one of the main reasons of performance deterioration. In this study, we look into the thermal effects during vapor absorption into single hygroscopic liquid desiccant droplets. Specifically, the effect of substrate conductivity on the transient heat and mass transfer process is analyzed in detail. The relative strength of the thermal effect and the solutal effect on the rate of vapor absorption is investigated and compared to the thermal effect by evaporative cooling taking place in pure water droplets. In the case of liquid desiccants, results indicate that the high thermal conductivity of copper substrates ensures more efficient heat removal, and the temperature at the droplet surface decreases more rapidly than that on Polytetrafluoroethylene (PTFE) substrates. As a result, the initial rate of vapor absorption on copper substrates slightly outweighs that on PTFE substrates. Further analysis by decomposing the vapor pressure difference indicates that the variation of vapor pressure caused by the temperature change during vapor absorption is much weaker than that induced by the concentration change. The conclusions demonstrate that a simplified isothermal model can be applied to capture the main mechanisms during vapor absorption into hygroscopic droplets even though it is evidenced to be unreliable for droplet evaporation..
5. Yuhong Chen, Alexandros Askounis, Vasileios Koutsos, Prashant Valluri, Yasuyuki Takata, Stephen K. Wilson, Khellil Sefiane, On the Effect of Substrate Viscoelasticity on the Evaporation Kinetics and Deposition Patterns of Nanosuspension Drops, Langmuir, 10.1021/acs.langmuir.9b02965, 36, 1, 204-213, 2020.01, This study investigates the evaporation of sessile pure water and nanosuspension drops on viscoelastic polydimethylsiloxane (PDMS) films. We varied the viscoelasticity of the PDMS films by controlling the curing ratio and categorized them into three types: Stiff (10:1, 20:1, 40:1), soft (60:1, 80:1), and very soft (100:1, 120:1, 140:1, 160:1). On stiff surfaces, pure water drops initially evaporate in a constant contact radius (CCR) mode, followed by a constant contact angle mode, and finally in a mixed mode of evaporation. Nanosuspension drops follow the same trend as water drops but with a difference toward the end of their lifetimes, when a short second CCR mode is observed. Complete evaporation of nanosuspension drops on stiff substrates leads to particle deposition patterns similar to a coffee ring with cracks and deposition tails. On soft surfaces, the initial spreading is followed by a pseudo-CCR mode. Complete evaporation of nanosuspension drops on soft substrates leads to deposits in the form of a uniform ring with a sharp ox-horn profile. Unexpectedly, the initial spreading is followed by a mixed mode on very soft substrates, on which wetting ridges (WRs) pulled up by the vertical component of surface tension are clearly observed in the vicinity of the contact line (CL). As the evaporation proceeds, the decreasing contact angle breaks the force balance in the horizontal direction at the CL and gives rise to a net horizontal force, which causes the CL to recede, transferring the horizontal force to the WR. Because of the viscoelastic nature of the very soft substrate, this horizontal force acting on the WR cannot be completely countered by the bulk of the substrate underneath. As a result, the WR moves horizontally in a viscous-flow way, which also enables the CL to be continuously anchored to the ridge and to recede relative to the bulk of the substrate. Consequently, a mixed mode of evaporation occurs. Complete evaporation of nanosuspension drops on very soft substrates leads to finger-like deposits..
6. Y. Kawano, T. Kuroki, N. Sakoda, M. Monde, Y. Takata, Thermal analysis of high-pressure hydrogen during the discharging process, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.08.167, 44, 49, 27039-27045, 2019.10, The transient temperature and pressure of hydrogen are measured during the hydrogen discharging process through an orifice in a high-pressure vessel. The initial pressures of hydrogen in the vessel are set to approximately 30, 60, and 100 MPa. The mass flow rate and heat flux between hydrogen and the inner wall of the vessel are theoretically estimated using fundamental equations and experimental results with accurate thermophysical properties of hydrogen. The generation of temperature distribution and flow due to heat transfer in the vessel during discharge is verified by numerical analysis. Further, the relationship between reference gas temperature and heat flux in the vessel during the release of high-pressure hydrogen is studied. The average heat flux in the vessel is calculated using experimental and numerical analysis. The appropriate reference temperature is obtained using the comparison of the average heat flux in the vessel. In addition, the dominant heat transfer mode during hydrogen discharge is investigated. Numerical analysis shows that natural convection is formed inside the vessel due to a decrease in temperature. The Nusselt numbers in this process are presented as a function of Rayleigh numbers which are obtained by the experimental results and mass and energy conservations. The relationship between the Nusselt and Rayleigh numbers agrees with the heat transfer correlations of natural convections..
7. Hideaki Teshima, Yasuyuki Takata, Koji Takahashi, Adsorbed gas layers limit the mobility of micropancakes, Applied Physics Letters, 10.1063/1.5113810, 115, 7, 2019.08, In contrast to surface nanobubbles, the properties of atomically flat gas phases such as micropancakes remain unclear. In this study, we investigated nanoscopic gas phases existing at the interface between highly ordered pyrolytic graphite and air-supersaturated pure water using high-sensitivity frequency-modulation atomic force microscopy (AFM). Micropancakes appeared on a disordered gas layer overlying an ordered gas layer and moved in the direction of AFM scanning. Their movement stopped at the edge of the disordered gas layers, whereas the two gas layers did not move at all. The limited mobility of micropancakes is explained by assuming that the disordered and ordered gas layers, which are composed of strongly adsorbed gas molecules, behave like solid surfaces, and that the surface heterogeneity between them results in a pinning effect..
8. Daniel Orejon, Alexandros Askounis, Yasuyuki Takata, Daniel Attinger, Dropwise Condensation on Multiscale Bioinspired Metallic Surfaces with Nanofeatures, ACS Applied Materials and Interfaces, 10.1021/acsami.9b06001, 11, 27, 24735-24750, 2019.07, Nonwetting surfaces engineered from intrinsically hydrophilic metallic materials are promising for self-cleaning, anti-icing, or condensation heat transfer applications where the durability of commonly applied hydrophobic coatings is an issue. In this work, we fabricate and study the wetting behavior and the condensation performance on two metallic nonwetting surfaces with varying number and size of roughness tiers without the need for further hydrophobic coating procedure. On one hand, the surface resembling a rose petal exhibits a sticky nonwetting behavior as drops wet the microscopic roughness features with consequent enhanced drop adhesion, which leads to filmwise condensation. On the other hand, the surface resembling a lotus leaf provides super-repellent nonwetting behavior prompting the continuous nucleation, growth, and departure of spherical drops in a dropwise condensation fashion. On a lotus leaf surface, the third nanoscale roughness tier (created by chemical oxidation) combined with ambience exposure prompts the growth of drops in the Cassie state with the benefit of minimal condensate adhesion. The two different condensation behaviors reported are well supported by a drop surface energy analysis, which accounts for the different wetting performance and the surface structure underneath the condensing drops. Further, we coated the above-mentioned surfaces with polydimethylsiloxane, which resulted in filmwise condensation due to the smoothening of the different roughness tiers. Continuous dropwise condensation on a hierarchical bioinspired lotus leaf metallic surface without the need for a conformal hydrophobic coating is hence demonstrated, which offers a novel path for the design and manufacture of noncoated metallic super-repellent surfaces for condensation phase change applications, among others..
9. Zhenying Wang, Daniel Orejon, Khellil Sefiane, Yasuyuki Takata, Coupled thermal transport and mass diffusion during vapor absorption into hygroscopic liquid desiccant droplets, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2019.01.084, 134, 1014-1023, 2019.05, Phase change phenomena at a droplet scale have gained extensive attention in recent years due to the unique aspects that can be exploited in a wide range of domestic and industrial applications. Different from existing studies on droplet evaporation and/or dropwise condensation, this work focuses on the mechanisms of vapor absorption into hygroscopic liquid desiccant droplets, which are of interest to many dehumidification and absorption processes. In particular we investigate the coupled heat and mass transport during vapor absorption into single droplets using optical imaging and infrared thermography. Driven by the vapor pressure difference between the ambient and the droplet surface, desiccant droplets grow due to water uptake. The droplet growth rate and final expansion ratio depend on the ambient temperature and relative humidity. After liquid desiccant droplet deposition onto the substrate, and as a consequence of the initial fast vapor absorption, droplets experience an increase in temperature. They then gradually cool down as a result of heat dissipation into the substrate and into the ambient combined with the decrease in the vapor absorption rate, i.e., heat of absorption. The temperature rise measured by infrared thermography is confirmed by the calculation of the heat of absorption for six representative environmental conditions. Furthermore the vapor pressure at the droplet surface is estimated taking account of the changes of interfacial temperature and salt concentration within the droplet bulk. As water absorbs into the droplets, the salt concentration decreases and so does the driving force for vapor diffusion and hence the heat of absorption. As a contrast, experiments with evaporating water droplets show different evolution of droplet profile, different dynamics of the triple contact line, as well as the occurrence of evaporative cooling. We conclude on the importance of taking account of the coupling mechanisms of absorptive heating and volume growth during vapor absorption into liquid desiccant droplets. Findings presented here provide a valuable extension to existing literature of phase change at the droplet scale, and contribute to a more complete understanding of the behaviors of liquid desiccant droplets in dehumidification processes..
10. Biao Shen, Takeshi Hamazaki, Wei Ma, Naoki Iwata, Sumitomo Hidaka, Atsushi Takahara, Koji Takahashi, Yasuyuki Takata, Enhanced pool boiling of ethanol on wettability-patterned surfaces, Applied Thermal Engineering, 10.1016/j.applthermaleng.2018.12.049, 325-331, 2019.02, Due to the considerably reduced boiling point, organic fluids such as ethanol provide an attractive alternative to water as the working fluid in two-phase thermal management systems for high-heat-flux applications. The state-of-the-art enhancement methods for ethanol boiling normally involve surface structure engineering. Here we report, for the first time, enhancement of nucleate boiling of ethanol using wettability-patterned surfaces. By depositing onto a polished copper surface an array of circular spots of superamphiphobic coating of modified halloysite nanotubes (HNT) with fluoropolymer, which was shown to repel low-surface-tension fluids, we managed to create a meaningful biphilic pattern of alternating hydrophobicity (with ethanol contact angle exceeding 100°) and hydrophilicity (with contact angle close to 0°) on the surface. Boiling heat transfer was found to be improved dramatically on the coated surface. Specifically, the onset of nucleate boiling was found to drop by more than 35%. Moreover, at 20 K surface superheat (above the boiling point), a maximum heat transfer enhancement over 300% compared with a plain copper surface occurred on the surface with a pitch-to-spot ratio close to 2.5. The significantly increased heat transfer rate of the biphilic surfaces could be attributed to facilitated bubble nucleation and stronger agitation effect..
11. Naoya Sakoda, Jiang Shiheng, Masaya Nakazaki, Yasuyuki Takata, Yukihiro Higashi, Thermodynamic properties of binary mixtures of Trifluoroethene (HFO1123) + 2,3,3,3-Tetrafluoroprop-1-ene (HFO1234yf), 25th IIR International Congress of Refrigeration, ICR 2019 ICR 2019 - 25th IIR International Congress of Refrigeration, 10.18462/iir.icr.2019.1608, 1782-1787, 2019.01, PvTx properties of a binary mixture of 50 mass% HFO1123 (trifluoroethene) + 50 mass% HFO1234yf (2,3,3,3-tetrafluoroprop-1-ene) were measured in the temperature range from 294 to 410 K, in the density range between 83 kg.m-3 and 905 kg.m-3, and at pressures up to 8.1 MPa by an isochoric method, and the obtained data are compared with an equation of state (EOS) compiled in REFPROP 10.0. In addition, the critical parameters and saturated densities of the mixture were measured. Vapor-liquid equilibrium of HFO1123 + HFO1234yf was also measured at temperatures from 273 to 313 K by a recirculation method, and the binary interaction parameter of a cubic EOS was determined..
12. Huacheng Zhang, Yutaku Kita, Dejian Zhang, Gyoko Nagayama, Yasuyuki Takata, Khellil Sefiane, Alexandros Askounis, Drop Evaporation on Rough Hot-Spots
Effect of Wetting Modes, Heat Transfer Engineering, 10.1080/01457632.2019.1640458, 2019.01, Hot-spots are a common occurrence in power electronics which become increasingly hotter as chips become denser. Novel cooling technologies are emerging to cope with this increasing heat load, which imbed a condenser to supply cooling drops to the evaporator resting on the hot-spots. Nonetheless, the evaporation process of the drops has been overlooked. Here, we conducted a series of experiments to understand how the evaporation and motion of drops are influenced by the wetting mode of rough hot-spots. We fabricated three different surfaces exhibiting full (Wenzel) or partial (Cassie–Baxter) wetting and the hot-spot is imposed by laser irradiation. We report a direct link between drop motion and wetting mode with the partial wetting drops being highly mobile, attributable to lower pinning energy based on an energy analysis. This study provides a framework for future modifications in hot-spot cooling to account for drop motion which should greatly influence the overall heat removal performance..
13. Zhenying Wang, Daniel Orejon, Khellil Sefiane, Yasuyuki Takata, Water vapor uptake into hygroscopic lithium bromide desiccant droplets
Mechanisms of droplet growth and spreading, Physical Chemistry Chemical Physics, 10.1039/c8cp04504f, 21, 3, 1046-1058, 2019.01, The study of vapor absorption into liquid desiccant droplets is of general relevance to a better understanding and description of vapor absorption phenomena occurring at the macroscale as well as for practical optimization of dehumidification and refrigeration processes. Hence, in the present work, we provide the first systematic experimental study on the fundamentals of vapor absorption into liquid desiccant at the droplet scale, which initiates a novel avenue for the research of hygroscopic droplet growth. More specifically we address the behavior of lithium bromide-water droplets on hydrophobic PTFE and hydrophilic glass substrates under controlled ambient conditions. Driven by the vapor pressure difference between the ambient air and the droplet interface, desiccant droplets absorb water vapor and increase in volume. To provide further insights on the vapor absorption process, the evolution of the droplet profile is recorded using optical imaging and relevant profile characteristics are extracted. Results show that, even though the final expansion ratio of droplet volume is only a function of relative humidity, the dynamics of contact line and the absorption rate are found to differ greatly when comparing data with varying substrate wettability. Droplets on hydrophilic substrates show higher absorption kinetics and reach equilibrium with the ambient much faster than those on hydrophobic substrates. This is attributed to the absorption process being controlled by solute diffusion on the droplet side and to the shorter characteristic length for the solute diffusion on hydrophilic substrates. Moreover, the apparent droplet spreading process on hydrophilic substrates when compared to hydrophobic ones is explained based on a force balance analysis near the triple contact line, by the change of liquid-vapor surface tension due to the increase in water concentration, and assuming a development of a precursor film..
14. Yoko Tomo, Qin Yi Li, Tatsuya Ikuta, Yasuyuki Takata, Koji Takahashi, Unexpected Homogeneous Bubble Nucleation near a Solid-Liquid Interface, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b09200, 122, 50, 28712-28716, 2018.12, We report a quasi-three-dimensional observation of electron-beam-induced nanobubbles inside a 1000 nm thick layer of water using the liquid cell electron microscopy. In the early stage of observation, heterogeneous bubble nucleation occurred, and small bubbles coalesced with the adjacent bubbles when they come in contact with each other. However, for the first time, we found that after prolonged electron beam irradiation heterogeneous nucleation did not occur more, and then homogeneous nucleation started even though a solid surface was available for heterogeneous nucleation. We conclude that the Ostwald ripening effect prevents heterogeneous nucleation from occurring and that the lower surface tension due to the generation of ions and radicals boosts the homogeneous nucleation. It was also discovered that the generation sites of homogeneous nucleation are beneath the three-phase contact lines of existing interfacial bubbles..
15. Tejaswi Josyula, Zhenying Wang, Alexandros Askounis, Daniel Mantecon Orejon, Harish Sivasankaran, Yasuyuki Takata, Pallab Sinha Mahapatra, Arvind Pattamatta, Evaporation kinetics of pure water drops
Thermal patterns, Marangoni flow, and interfacial temperature difference, Physical Review E, 10.1103/PhysRevE.98.052804, 98, 5, 2018.11, We report a systematic study of the role of Marangoni convection in the evaporation kinetics of pure water drops, considering the influence of the heating regime and surface wettability. Marangoni flows were induced via heating under constant wall temperature (uniform heating) and constant heat flux (local heating) regimes below the drops. To visualize the thermal patterns emerging during the evaporation, we employed infrared thermography and we captured the evolution of the drop profile with a CCD camera to follow the evaporation kinetics of each drop. We observed a strong correlation between the temperature difference within the drop and the evolution of the drop shape during different modes of evaporation (i.e., constant radius, angle, or stick-slip) resulting in different Marangoni flow patterns. Under uniform heating, stable recirculatory vortices due to Marangoni convection emerged at high temperature, but they faded at later stages of the evaporation process. On the other hand, in the localized heating case, the constant heat flux resulted in a rapid increase in the temperature difference within the drop capable of sustaining Marangoni flows throughout the evaporation. Surface wettability was found also to play a role in both the emergence of the Marangoni flows and the evaporation kinetics. In particular, recirculatory flows in drops on hydrophobic surfaces were stronger when compared to flows on hydrophilic surfaces for both uniform and local heating. To quantify the effect of the heating mode and the importance of Marangoni flows, we calculated the evaporative flux for each case and found it to be much higher in the localized heating case. Evaporative flux depends on both diffusion and natural convection of the vapor phase to the ambient. Hence, we estimated the Grashof number for each case and found a strong relation between natural convection in the vapor phase and heating regime or Marangoni convection in the liquid phase. Subsequently, we demonstrate the limitation of the previously reported diffusion-only model in describing the evaporation of heated drops..
16. Biao Shen, Masayuki Yamada, Tomosuke Mine, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Depinning of bubble contact line on a biphilic surface in subatmospheric boiling
Revisiting the theories of bubble departure, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2018.06.030, 126, 715-720, 2018.11, Boiling suffers from inefficient intermittent cycles of bubble generation under subatmospheric conditions. Such deterioration in heat transfer rates can be alleviated but not completely eliminated by use of mixed-wettability (biphilic) surfaces. Here we study bubble dynamics on a single hydrophobic spot in low-pressure pool boiling. The results reveal an interesting transition in bubble departure behavior from the surface-driven mode to the drag-driven mode, which correlates closely with the dynamic state of the three-phase contact line on the surface. Based on the force-balance argument, a simple model is derived to map the contact-line mobility during bubble growth. It is found that below a certain threshold pressure, the bubble base expansion is increasingly likely to overcome the strong pinning of the contact line at the interface between the hydrophobic and hydrophilic regions. That could lead to total removal of vapor residues from the surface and cause deactivation of the nucleation site, which portends the eventual takeover of intermittent boiling on the biphilic surface..
17. Yutaku Kita, Coinneach Mackenzie Dover, Alexandros Askounis, Yasuyuki Takata, Khellil Sefiane, Drop mobility on superhydrophobic microstructured surfaces with wettability contrasts, Soft Matter, 10.1039/c8sm01762j, 14, 46, 9418-9424, 2018.11, Manipulation of drop motion has attracted considerable attention recently as it is pertinent to industrial/biological applications such as microfluidics. Wettability gradients/contrasts applied to microtextured, superhydrophobic surfaces are probable candidates for engineering drop motion by virtue of their wettability controllability and low contact angle hysteresis. In the present work, we present a systematic study of drop mobility induced via wettability contrasts. A millimetre-sized water drop, placed on the boundary between two surfaces with distinct, uniform arrays of pillars, immediately moved toward the surface more densely populated with asperities, which was relatively more hydrophilic. The velocity of the motion was found to increase proportionally with the difference in pillar densities on each surface, in circumstances where the rear side surface had sufficiently small contact angle hysteresis. To elucidate the underlying mechanism of drop motion, we implemented a surface energy analysis for each motion event. Motion was initiated by the excess surface free energy due to drop deformation and directed in favour of energy minimisation. Lastly, we propose a theory to predict the direction of the drop which at the same time acts as the criterion for the motion to ensue..
18. Biao Shen, Jiewei Liu, Junichiro Shiomi, Gustav Amberg, Minh Do-Quang, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Effect of dissolved gas on bubble growth on a biphilic surface
A diffuse-interface simulation approach, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2018.06.043, 126, 816-829, 2018.11, In this paper, we numerically study pool boiling of a binary (water and nitrogen) mixture on a surface endowed with a combination of hydrophobicity and hydrophilicity (i.e., the so called biphilic surface). Here we adopt a numerical approach based on the phase field theory, where the vapor-liquid interface is assumed to be of a finite thickness (hence diffusive in nature) and requires no explicit tracking schemes. The theoretical modeling of two-phase heat and mass transfer in water diluted with nitrogen demonstrates the significant impact of impurities on bubble dynamics. The simulations show that locally high concentrations of nitrogen gas within the vapor bubble is essential to weakening the condensation effect, which results in sustained bubble growth and ultimately (partial) departure from the surface under the artificially enlarged gravity. Simply increasing the solubility of nitrogen in water, however, turns out to be counterproductive because possible re-dissolution of the aggregated nitrogen by the bulk water could deprive the bubble of vital gas contents, leading instead to continuous bubble shrinkage and collapse. Additionally, it is found that with the significant accumulation of nitrogen, the bubble interface is increasingly dominated by a strong interfacial thermocapillary flow due to the Marangoni effect..
19. Tejaswi Josyula, Zhenying Wang, Alexandros Askounis, Daniel Orejon, Sivasankaran Harish, Yasuyuki Takata, Pallab Sinha Mahapatra, Arvind Pattamatta, Evaporation kinetics of pure water drops
Thermal patterns, Marangoni flow, and interfacial temperature difference, Physical Review E, 10.1103/PhysRevE.98.052804, 98, 5, 2018.11, We report a systematic study of the role of Marangoni convection in the evaporation kinetics of pure water drops, considering the influence of the heating regime and surface wettability. Marangoni flows were induced via heating under constant wall temperature (uniform heating) and constant heat flux (local heating) regimes below the drops. To visualize the thermal patterns emerging during the evaporation, we employed infrared thermography and we captured the evolution of the drop profile with a CCD camera to follow the evaporation kinetics of each drop. We observed a strong correlation between the temperature difference within the drop and the evolution of the drop shape during different modes of evaporation (i.e., constant radius, angle, or stick-slip) resulting in different Marangoni flow patterns. Under uniform heating, stable recirculatory vortices due to Marangoni convection emerged at high temperature, but they faded at later stages of the evaporation process. On the other hand, in the localized heating case, the constant heat flux resulted in a rapid increase in the temperature difference within the drop capable of sustaining Marangoni flows throughout the evaporation. Surface wettability was found also to play a role in both the emergence of the Marangoni flows and the evaporation kinetics. In particular, recirculatory flows in drops on hydrophobic surfaces were stronger when compared to flows on hydrophilic surfaces for both uniform and local heating. To quantify the effect of the heating mode and the importance of Marangoni flows, we calculated the evaporative flux for each case and found it to be much higher in the localized heating case. Evaporative flux depends on both diffusion and natural convection of the vapor phase to the ambient. Hence, we estimated the Grashof number for each case and found a strong relation between natural convection in the vapor phase and heating regime or Marangoni convection in the liquid phase. Subsequently, we demonstrate the limitation of the previously reported diffusion-only model in describing the evaporation of heated drops..
20. Deendarlianto, Yasuyuki Takata, Arif Widyatama, Akmal Irfan Majid, Ardi Wiranata, Adhika Widyaparaga, Masamichi Kohno, Sumitomo Hidaka, Indarto, The interfacial dynamics of the micrometric droplet diameters during the impacting onto inclined hot surfaces, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2018.05.023, 126, 39-51, 2018.11, The interfacial dynamics of the micrometric size liquid droplets during impact onto inclined hot surfaces have been experimentally studied. The inclination angles were varied at 15° 30° and 45° from horizontal for surface temperatures were decreasing from 500 °C to 100 °C. The droplet diameters tested were 500 μm and 700 μm. The tested material was stainless steel-grade 304 (SUS 304) with varying surface roughness ranging from Ra 0.04 up to Ra 10. The interfacial dynamics during the impact onto inclined hot surfaces were investigated by using a high-speed video camera with the frame speed of 15,000 fps. The objectives of this study are to provide insight into the dynamic behaviors of contact angles and dependence of importance parameters at various surface temperatures. It was found that depending on the surface temperature the droplet evaporation and its bouncing process play an important role on the droplet detachment mechanisms from the inclined surface. Three transient regions of the interfacial evolution during the micrometric droplets impacting onto oblique hot surface were identified. Moreover, the contribution of the important physical parameters, such as, advancing and receding contact angles on the interfacial dynamics are presented..
21. Yutaku Kita, Coinneach Mackenzie Dover, Alexandros Askounis, Yasuyuki Takata, K. Sefiane, DROP MOBILITY ON SUPERHYDROPHOBIC SURFACES WITH WETTABILITY CONTRASTS, 16th International Heat Transfer Conference Proceedings of the 16th International Heat Transfer Conference 16, 10.1615/IHTC16.cod.023512, 2433-2438, 2018.08.
22. Alexandros Askounis, Huacheng Zhang, Dejian Zhang, Yutaku Kita, Gyoko Nagayama, Masamichi Kohno, Yasuyuki Takata, K. Sefiane, UNVEILING THERMOCAPILLARY CONVECTION IN PURE WATER DROPS, Proceedings of the 16th International Heat Transfer Conference 16, 10.1615/IHTC16.bae.023953, 809-814, 2018.08.
23. Suhaila Hussain, Suhaimi Illias, Yasuyuki Takata, Stefan tube evaporation
Numerical model validation for diffusion-controlled evaporation process, International Review of Mechanical Engineering, 10.15866/ireme.v12i7.14470, 12, 7, 620-626, 2018.07, Evaporation is a complex process that, among others, involves the change of phase from liquid to vapour. Although have been extensively studied, the evaporation process has yet to be fully understood. To assist in this, a numerical model had been developed to simulate the process in which various fluid flow governing equations are integrated together and solved. In order to validate the developed model, the well-known 1-dimensional Stefan diffusion problem is solved as it has a known analytical solution. The Stefan diffusion problem is simulated for both water and the fluorinate compound FC-72, each representing the case for a non-volatile and volatile fluid, respectively. The mass flow rates obtained from the simulation are compared to the existing analytical solution while the concentration and velocity profiles are compared to theories and experimental findings from other researchers. The comparisons showed good agreement between the numerical model, the analytical solution and experimental findings thereby validating the developed evaporation model..
24. Vipul Sharma, Daniel Orejon, Yasuyuki Takata, Venkata Krishnan, Sivasankaran Harish, Gladiolus dalenii Based Bioinspired Structured Surface via Soft Lithography and Its Application in Water Vapor Condensation and Fog Harvesting, ACS Sustainable Chemistry and Engineering, 10.1021/acssuschemeng.8b00815, 6, 5, 6981-6993, 2018.05, Water collection via heterogeneous condensation and fog harvesting has important implications in everyday life and in several industrial applications. Recently, the unique combination of surface morphology and wettability exhibited by natural and biological species is receiving increasing attention from the scientific community. Surface morphology of such species exhibits unique micro- and nanostructure arrangements, which play a paramount role in water vapor condensation and fog harvesting. In this work, we focus on the design and replication of the bioinspired surface Gladiolus dalenii (G. dalenii) using inexpensive, facile and scalable soft lithography fabrication technique. The extent of micro- and nanostructure surface replication is evaluated using scanning electron microscopy and 3D laser optical microscopy. In addition, we compare the performance of G. dalenii leaf and its bioinspired replica during droplet condensation at the microscale using environmental scanning electron microscopy and optical microscopy and also its fog harvesting behavior. Droplet nucleation and growth is investigated in detail and correlated with the unique surface micro- and nanostructures arranged in a hierarchical manner on such surfaces when compared to smooth control sample. In addition, the different water collection performance on fixated and on replicated G. dalenii, as well as on the smooth control sample is compared and demonstrated by the surface energy analysis proposed. To conclude, by taking advantage of the unique G. dalenii surface morphology, this work successfully demonstrates the excellent condensation heat transfer and fog harvesting behavior of bioinspired functional surfaces fabricated using soft lithography when compared to the flat configuration. In addition, we also demonstrate the near-accurate replication of the microsurface structures and of the governing mechanisms behind condensation and fog harvesting..
25. T. Kuroki, N. Sakoda, K. Shinzato, M. Monde, Y. Takata, Dynamic simulation for optimal hydrogen refueling method to Fuel Cell Vehicle tanks, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2018.01.111, 43, 11, 5714-5721, 2018.03, A dynamic simulation approach to investigate an optimal hydrogen refueling method is proposed. The proposed approach simulates a transient temperature, pressure and mass flow rate of hydrogen flowing inside filling equipment in an actual station during the refueling process to an Fuel Cell Vehicle (FCV) tank. The simulation model is the same as in an actual hydrogen refueling station (HRS), and consists of a Break-Away, a hose, a nozzle, pipes and an FCV tank. Therefore, we can set actual configurations and thermal properties to the simulation model, and then simulate the temperature, pressure and mass flow rate of hydrogen passing through each position based on the supply conditions (temperature and pressure) at the Break-Away. In this study, the simulated temperature, pressure and mass flow rate are compared with the corresponding experimental data. Therefore, we show that the dynamic simulation approach can accurately obtain those values at each position during the refueling process and is an effective step in proposing the optimal refueling method..
26. Yoko Tomo, Alexandros Askounis, Tatsuya Ikuta, Yasuyuki Takata, Khellil Sefiane, Koji Takahashi, Superstable Ultrathin Water Film Confined in a Hydrophilized Carbon Nanotube, Nano Letters, 10.1021/acs.nanolett.7b05169, 18, 3, 1869-1874, 2018.03, Fluids confined in a nanoscale space behave differently than in the bulk due to strong interactions between fluid molecules and solid atoms. Here, we observed water confined inside "open" hydrophilized carbon nanotubes (CNT), with diameter of tens of nanometers, using transmission electron microscopy (TEM). A 1-7 nm water film adhering to most of the inner wall surface was observed and remained stable in the high vacuum (order of 10-5 Pa) of the TEM. The superstability of this film was attributed to a combination of curvature, nanoroughness, and confinement resulting in a lower vapor pressure for water and hence inhibiting its vaporization. Occasional, suspended ultrathin water film with thickness of 3-20 nm were found and remained stable inside the CNT. This film thickness is 1 order of magnitude smaller than the critical film thickness (about 40 nm) reported by the Derjaguin-Landau-Verwey-Overbeek theory and previous experimental investigations. The stability of the suspended ultrathin water film is attributed to the additional molecular interactions due to the extended water meniscus, which balances the rest of the disjoining pressures..
27. Yukihiro Higashi, Naoya Sakoda, Md Amirul Islam, Yasuyuki Takata, Shigeru Koyama, Ryo Akasaka, Measurements of Saturation Pressures for Trifluoroethene (R1123) and 3,3,3-Trifluoropropene (R1243zf), Journal of Chemical and Engineering Data, 10.1021/acs.jced.7b00818, 63, 2, 417-421, 2018.02, Saturation pressures for new low global warming potential refrigerants trifluoroethene (R1123, CF2= CHF) and 3,3,3-trifluoropropene (R1243zf, CF3CH=CH2) were measured by the isochoric method for temperatures between 278 and 377 K. Temperature was measured with a 25 standard platinum resistance thermometer on ITS-90. Pressure was measured with a digital quartz pressure transducer. The experimental uncertainties in temperature and pressure are estimated to be 5 mK and 1 kPa (k = 2), respectively. New saturation-pressure correlations for the refrigerants have been formulated based on the present saturation-pressure data. The critical pressures of R1123 and R1243zf were also determined..
28. Bambang Joko Suroto, Masamichi Kohno, Yasuyuki Takata, Surface wettability and subcooling on nucleate pool boiling heat transfer, 1st International Conference and Exhibition on Powder Technology Indonesia, ICePTi 2017 1st International Conference and Exhibition on Powder Technology Indonesia, ICePTi 2017, 10.1063/1.5021240, 2018.02, The effect of varying surface wettabilities and subcooling on nucleate pool boiling heat transfer at intermediate heat flux has been examined and investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0, 5 and 10 K, respectively. The three types of heat transfer block were used that are bare surface/hydrophilic (polished copper), superhydrophilic/TiO2-coated on copper and hydrophobic/PTFE surface. The experimental results will be examined by the existing model. The results show that the heat transfer performance of surfaces with PTFE coating is better at low heat flux. While for an intermediate heat flux, superhydrophilic surface (TiO2) is superior compared to hydrophilic and hydrophobic surfaces. It is observed that the heat transfer performance is decreasing when the sub cooling degree is increased..
29. T. Kuroki, N. Sakoda, K. Shinzato, M. Monde, Y. Takata, Temperature rise of hydrogen storage cylinders by thermal radiation from fire at hydrogen-gasoline hybrid refueling stations, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2017.12.072, 43, 5, 2531-2539, 2018.02, This study focuses on two types of hydrogen-gasoline hybrid refueling stations, and a risk assessment study on thermal radiation is carried out with a fire at each hybrid station. One of the hybrid stations has bare hydrogen storage cylinders, and the other has container walls around the cylinders. We calculate radiative flux to the cylinders from the fire occurring at the gasoline refueling machines in each hybrid station. Additionally, we calculate the temperature rise of the cylinders based on the obtained radiative flux. To evaluate a dangerous case for hybrid stations, we calculate the radiative flux and temperature rise using a large scale and high temperature fire. Based on our analysis, we find that the container walls can greatly insulate the radiative flux. Therefore, we show that we are able to keep the temperature of the cylinders below the hazardous temperature of 358 K by installing container walls around them..
30. Hideaki Teshima, Koji Takahashi, Yasuyuki Takata, Takashi Nishiyama, Wettability of AFM tip influences the profile of interfacial nanobubbles, Journal of Applied Physics, 10.1063/1.5010131, 123, 5, 2018.02, To accurately characterize the shape of interfacial nanobubbles using atomic force microscopy (AFM), we investigated the effect of wettability of the AFM tip while operating in the peak force tapping (PFT) mode. The AFM tips were made hydrophobic and hydrophilic by Teflon AF coating and oxygen plasma treatment, respectively. It was found that the measured base radius of nanobubbles differed between AFM height images and adhesion images, and that this difference depended on the tip wettability. The force curves obtained during the measurements were also different depending on the wettability, especially in the range of the tip/nanobubble interaction and in the magnitude of the maximum attractive force in the retraction period. The difference suggests that hydrophobic tips penetrate the gas/liquid interface of the nanobubbles, with the three phase contact line being pinned on the tip surface; hydrophilic tips on the other hand do not penetrate the interface. We then quantitatively estimated the pinning position and recalculated the true profiles of the nanobubbles by comparing the height images and adhesion images. As the AFM tip was made more hydrophilic, the penetration depth decreased and eventually approached zero. This result suggests that the PFT measurement using a hydrophilic tip is vital for the acquisition of reliable nanobubble profiles..
31. Hongbin He, Biao Shen, Sumitomo Hidaka, Koji Takahashi, Yasuyuki Takata, A loop thermosyphon with hydrophobic spots evaporator surface, ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2018 ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2018, 2018.01, Heat transfer characteristic of a closed two-phase thermosyphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling improves heat transfer coefficient (HTC) a lot compared to single-phase liquid cooling. The evaporator surfaces, coated with a pattern of hydrophobic circle spots (non-electroplating Ni-PTFE, 0.5~2 mm in diameter and 1.5-3 mm in pitch) on Cu substrates, achieve very high heat transfer coefficient and lower the incipience temperature overshoot using water as the working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests with heat loads (30 W to 260 W) reveals the coated surfaces enhance nucleate boiling performance by increasing the bubbles nucleation sites density. Hydrophobic circle spots coated surface with diameter 1 mm, pitch 1.5 mm achieves the maximal heat transfer enhancement with the minimum boiling thermal resistance as low as 0.03 K/W. The comparison of three evaporator surfaces with same spot parameters but different coating materials is carried out experimentally. Ni-PTFE coated surface with immersion method performs the optimal performance of the thermosyphon..
32. Taichi Kuroki, Kiyoshi Handa, Masanori Monde, Shigehiro Yamaguchi, Kane'I Shinzato, Yasuyuki Takata, Naoya Sakoda, Dynamic Simulation Software for Prediction of Hydrogen Temperature and Pressure during Fueling Process, 2018 SAE World Congress Experience, WCX 2018 SAE Technical Papers, 10.4271/2018-01-1304, 2018-April, 2018.01, In this study, in order to relax the pre-cooling regulations at hydrogen fueling stations, we develop a software algorithm to simulate an actual hydrogen fueling process to Fuel Cell Vehicle (FCV) tanks. The simulation model in the software consists of the same filling equipment found at an actual hydrogen fueling station. Additionally, the same supply conditions (pre-cooling temperature, pressure and mass flow rate) as at a hydrogen fueling station were set to the simulation model. Based on the supply conditions, the software simulates the temperature and pressure of hydrogen in each part of filling equipment. In order to verify the accuracy of the software, we compare the temperature and pressure simulated at each stage of the filling process with experimental data. We show that by using the software it is possible to accurately calculate the hydrogen temperature and pressure at each point during the fueling process. Subsequently, we carry out a sensitive analysis of the filling equipment with large heat capacity, the initial temperature in the FCV tank and the pre-cooling temperature, and then propose an effective step to relax the regulation regarding the pre-cooling temperature. KeywordsFilling equipment, Hydrogen fueling station, Hydrogen temperature, Hydrogen pressure, Pre-cooling temperature..
33. Daniel Orejon, Yota Maeda, Fengyong Lv, Peng Zhang, Yasuyuki Takata, Effect of microstructures on superhydrophobic and slippery lubricant-infused porous surfaces during condensation phase-change, ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2018 ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2018, 2018.01, Superhydrophobic surfaces (SHSs) and slippery lubricant-infused porous surfaces (SLIPSs) are receiving increasing attention for their excellent anti-icing, anti-fogging, self-cleaning and condensation heat transfer properties. The ability of such surfaces to passively shed and repel water is mainly due to the low-adhesion between the liquid and the solid surface, i.e., low contact angle hysteresis, when compared to hydrophilic or to hydrophobic surfaces. In this work we investigated the effect of surface structure on the condensation performance on SHSs and SLIPSs. Three different SHSs with structures varying from the micro- to the nano-scale were fabricated following easy and scalable etching and oxidation growth procedures. The condensation performance on such surfaces was evaluated by optical microscopy in a temperature and humidity controlled environmental chamber. On SHSs important differences on the size and on the number of the coalescing droplets required for the jump to ensue were found when varying the surface structure underneath the condensing droplets. A surface energy analysis is proposed to account for the suppression of the droplet-jumping performance in the presence of microstructures. On other hand, by impregnating the same SHSs with a low surface tension oil, i.e., SLIPSs, the adhesion between the condensate and the SLIPSs can be further reduced. On SLIPSs slight differences on the droplet density over time and shedding performance upon the inclusion of microstructures were observed. Droplets were found to shed faster and with smaller diameters on SLIPSs in the presence of microstructures when compared to solely nanostructured SLIPSs. We conclude that on SHSs the droplet-jumping performance of micrometer droplets is deteriorated in the presence of microstructures with the consequent decrease in the heat transfer performance, whereas on SLIPSs the droplet self-removal is actually improved in the presence of microstructures..
34. Biao Shen, Masayuki Yamada, Tomosuke Mine, Sumitomo Hidaka, Junichiro Shiomi, Gustav Amberg, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Enhanced boiling heat transfer on surfaces patterned with mixed wettability, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 1379-1386, 2018.01, Amongst an extensive collection of surface characteristics that could affect boiling performance, surface wettability (as measured by the contact angle with water) proves to play a unique role in potentially manipulating bubble behavior to the advantage of higher heat transfer rates. In this study, we show experimentally that controlled bubble behavior be realized under the surface design incorporating these two characteristics (namely, by coating an array of hydrophobic spots on a hydrophilic substrate), which leads to a great enhancement in boiling heat transfer under various conditions. In reduced-pressure pool boiling, the strong pinning of the bubble contact line at the border between the hydrophilic and hydrophobic regions manages to prevent total deactivation of nucleation sites. As a result, the deleterious transition to intermittent boiling is effectively delayed, whereby no heat transfer deterioration occurs until a very low pressure of about 8 kPa is reached. Moreover, in subcooled boiling, bubble growth on a patterned surface is found to be facilitated by a pronounced presence of dissolved gas in defiance of exhaustive degassing efforts through continuous boiling, thanks to an unusually strong retention of gas contents by the hydrophobic surface. As experimental and numerical evidence show, only bubbles with sufficiently high concentrations of gas components (i.e., causing weakened condensation) are able to grow large enough on the hydrophobic surface such that periodic pinch-offs might take place, which is responsible for most of the initial heat transfer enhancement before large-scale bubble nucleation starts on the hydrophilic surface as well..
35. Hongbin He, Biao Shen, Liangyu Chen, Sumitomo Hidaka, Koji Takahashi, Masamichi Kohno, Yasuyuki Takata, Heat transfer enhancement of a loop thermosyphon with a hydrophobic spot-coated surface, Journal of Thermal Science and Technology, 10.1299/jtst.2018jtst0011, 13, 1, 2018.01, Heat transfer characteristic of a closed two-phase thermosyphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling is widely used in application of thermal engineering and considerably more efficient than single-phase liquid cooling. The evaporator surfaces, coated with a pattern of hydrophobic circular spots (0.5 - 2 mm in diameter and 1.5 - 3 mm in pitch) on Cu substrates, achieve very high heat transfer coefficient and low incipience temperature overshoot with water as working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests under heat loads 30 W to 260 W reveal the coated surfaces enhance nucleate boiling performance by increasing the bubbles nucleation-site density. The surface with hydrophobic spots with diameter 1 mm and pitch 1.5 mm achieves the maximal heat transfer enhancement with the minimum boiling thermal resistance as low as 0.03 K/W. A comparison of three evaporator surfaces with identical wettability patterns but with different surface topographies and coating thicknesses is carried out experimentally. The results show superior heat transfer rates and wear resistance on the surface coated with HNTs spots thanks to the large contact angle, great thickness, and durability of the coating layer..
36. Hideaki Teshima, Takashi Nishiyama, Yasuyuki Takata, Koji Takahashi, Influence of surface wettability and nanostructure on the generation of interfacial nanobubbles, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 6909-6914, 2018.01, Interfacial nanobubbles were first speculated in 1994 and experimentally confirmed in 2000 by atomic force microscopy (AFM) measurements. It was recently proposed that the onset of boiling with the very low superheat on hydrophobic surface could be explained by assuming the existence of interfacial nanobubbles. To reduce the superheat and enhance the reliability of boiling heat transfer, the control of the generation of interfacial nanobubbles is indispensable. In this study, we measured the interfacial nanobubbles by AFM and examined the influence of surface wettability and nanostructure on their generation. First, we measured the spherical-cap shaped nanobubbles generated on the HOPG surface. It was observed that the nanobubbles only generate on the hydrophobic terraced area and do not cross the nanosized hydrophilic steps. Next, we prepared the hydrophilic-hydrophobic hybrid surfaces and generated the nanobubbles on those. As a result, the range of nanobubble generation clearly changed by the difference of wettability between adjacent surfaces. These results show that the generation of interfacial nanobubbles can be controlled by the surface processing of the substrate and can be expected to be applied to boiling heat transfer..
37. Daniel Orejon, Yota Maeda, Fengyong Lv, Peng Zhang, Yasuyuki Takata, Optimization of structure on condensation on suherphydrophoibic surfaces (SHSs) and slippery lubricant-infused porous surfaces (SLIPS), 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 2425-2432, 2018.01, Superhydrophobic Surfaces (SHSs) and Slippery Lubricant-Infused Porous Surfaces (SLIPSs) are proposed as excellent anti-icing, self-cleaning and condensation heat transfer surfaces due to their ability to repel water. The low droplet adhesion on SHSs and SLIPs is due to the low contact angle hysteresis displayed between the condensate and the surface, when compared to hydrophobic and/or to hydrophilic surfaces. In the case of SHSs, their extreme low adhesion is owed to the presence of air entrapped in between the condensate droplets and the surface, whereas in the case of SLIPS, their inherent low adhesion is due to the presence of a low surface energy lubricant oil in between the micro- and/or the nano-structures and the condensate. As a consequence, on both surfaces the condensate easily sheds by gravity and in the case of SHSs by coalescence-induced droplet-jumping. In this paper we investigate the condensation behavior on engineered SHSs and SLIPSs with structural roughness varying from the micro- to the nano-scale. Experimental observations and energy analysis is presented to demonstrate the different condensation performance observed depending on the surface structural finish underneath the condensate. We report the enhancement in the coalescence-induced droplet-jumping performance on SHSs and the greater theoretical heat transfer performance on SLIPSs. We conclude on the importance of taking into account the microstructures underneath the condensate for the optimum design of both SHSs and SLIPS..
38. T. Kuroki, Naoya Sakoda, K. Shinzato, M. Monde, Yasuyuki Takata, Prediction of transient temperature of hydrogen flowing from pre-cooler of refueling station to inlet of vehicle tank, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2017.11.033, 43, 3, 1846-1854, 2018.01, A thermodynamic analytical approach is proposed to obtain the transient temperature rise of hydrogen when pre-cooled hydrogen is heated through filling equipment at a refueling station. In this approach, the filling equipment is assumed to be a simple and straight pipeline, and the heat balance based on the thermodynamics for hydrogen flowing in the pipeline is analyzed. The internal surface temperature of the pipeline wall is required to calculate the heat flux into hydrogen. Therefore, we propose a solution to obtain the temperature distribution in the pipeline wall when hydrogen with lower temperature than the pipeline flows unsteadily. Based on the proposed solution, we calculate the heat flux and acquire the hydrogen temperature. The hydrogen temperatures predicted by this approach are compared with experimental data for the temperature rise of hydrogen heated through actual filling equipment, and a good agreement is shown. Thus, we show that this approach is useful for simulating the temperature rise of hydrogen flowing in the filling equipment..
39. Yutaku Kita, Yuya Okauchi, Yuki Fukatani, Daniel Mantecon Orejon, Masamichi Kohno, Yasuyuki Takata, Khellil Sefiane, Quantifying vapor transfer into evaporating ethanol drops in a humid atmosphere, Physical Chemistry Chemical Physics, 10.1039/c8cp02521e, 20, 29, 19430-19440, 2018.01, The effect of ambient temperature and relative humidity on the dynamics of ethanol drop evaporation is investigated. Although drop evaporation of mixtures and pure fluids has been extensively studied, very little is known about the transition from a pure fluid to a binary mixture following transfer of a second component present in the atmosphere. This is of importance for industrial, biological and medical applications where the purity of the solvent is paramount. Adsorption-absorption and/or condensation of water into ethanol drops during evaporation is presented through direct quantification of the drop composition in time. In particular, we combine drop profile measurements with Gas Injection Chromatography (GIC) to directly quantify the amount of ethanol evaporated and that of water intake over time. As expected, drops evaporate faster at higher temperatures since both the ethanol saturation concentration and the vapor diffusion coefficient are directly proportional to temperature. On the other hand, increases in the ethanol evaporation rate and in the water intake are observed at higher relative humidity. The increase in ethanol evaporation at higher relative humidity is interpreted by the greater diffusion coefficient of ethanol into humid air when compared to dry air. Moreover, as ethanol evaporates in a high humidity environment, the drop interfacial temperature falls below the dew point due to evaporative cooling and water condenses compared to lower humidity conditions. As a consequence of the heat released by adsorption-absorption and/or condensation, a greater temperature is reported at the liquid-vapor interface as confirmed by IR thermography, inducing a greater ethanol saturation concentration at the surface and hence a greater driving force for evaporation. By coupling the drop profile and the composition of ethanol and water within the drop, we propose a combined evaporation-adsorption/absorption and/or condensation empirical correlation. The proposed correlation accounts for: the decreases in ethanol concentration due to water adsorption-absorption and/or condensation, the diffusion coefficient dependence on relative humidity, and the amount of water intake during evaporation. The proposed empirical correlation agrees remarkably well with experimental observations..
40. Yoko Tomo, Alexandros Askounis, Khellil Sefiane, Yasuyuki Takata, Koji Takahashi, Study on liquid-gas interface at nanoscale using transmission electron microscopy, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 1169-1174, 2018.01, Control for the bubble nucleation at the onset of nucleate boiling (ONB) ensures the stable start of boiling heat transfer. However, the bubble nucleation mechanism at the ONB remains unclear, because of the difficulty of in-situ observation, which is due to the small size of nucleation. Thus, in order to break through the current technological barrier of boiling heat transfer, a new experimental technique enabling the investigation of the dynamics of bubbles near the solid-liquid interface is highly desirable. Liquid cell electron microscopy is the most useful method for the in-situ observation of liquid samples at the nanoscale. We prepared a closed liquid cell fabricated using MEMS technology and observed the generation and growth of bubbles at the nanoscale and in real time using transmission electron microscopy (TEM). In the growing process, the water meniscus between smaller bubbles becomes thinner and thinner and eventually ruptures. However, when the bubbles grow, the meniscus between larger bubbles do not rupture and the bubble overlaps with others, suggesting that thin meniscus can be stable only in the case of larger bubbles because of the difference of the curvature of their liquid-gas interfaces between smaller bubbles and larger bubbles. Our experimental results lead to the insight of the mechanism of the stability and the phase change phenomena at the liquid-gas interface at the nanoscale..
41. Sivasankaran Harish, Daniel Orejon, Yasuyuki Takata, Masamichi Kohno, Thermal conductivity enhancement of phase change nanocomposites in solid and liquid state with nano carbon inclusions, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 8866-8872, 2018.01, Lauric acid based phase change nanocomposites with chemically functionalized graphene nanoplatelets (GnPs), multi-walled carbon nanotubes (MWCNTs) and single walled carbon nanohorns (SWCNHs) were prepared and its thermal conductivity was measured using transient hot wire method. We found that inclusion of graphene nanoplatelets increase the thermal conductivity of phase change nanocomposites by a factor of 2.3 at a loading of 1 vol %. We also show contrasting enhancements in thermal conductivity of such nanocomposites in the solid and liquid phase for the same loading of SWCNHs inclusions. Maximum thermal conductivity enhancement of SWCNHs inclusions in solid and liquid phase at 2 vol % is found to be ~37% and ~11% respectively. The thermal conductivity enhancement was significantly higher in the solid state than the liquid state of the material for all the nano composites. Thermal conductivity enhancement results were compared with the effective medium theory calculations considering the role of interfacial thermal resistance between the nanomaterial and the surrounding host matrix. The model calculations show that the interfacial thermal resistance significantly limits the thermal conductivity enhancement in the liquid state compared to the solid state. The model calculations also show that interfacial thermal resistance is an order of magnitude higher at the solid-liquid interface compared to that of solid-solid interface which leads to a contrasting thermal conductivity enhancement in liquid and solid state of the nanocomposites..
42. Alexandros Askounis, Huacheng Zhang, Dejian Zhang, Yutaku Kita, Gyoko Nagayama, Masamichi Kohno, Yasuyuki Takata, Khellil Sefiane, Unveiling thermocapillary convection in pure water drops, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 809-814, 2018.01, The existence of thermocapillary/Marangoni convection in pure water drops has been a hotly debated area over the last few years. In this paper, we report the induction of Marangoni convection in pure water drops by localized laser heating and visualized via high speed infrared and optical cameras. The optical camera recorded the evolution of drop shape over time and the infrared camera provided the spatiotemporal evolution of the temperature across the surface of the water drop. Localized heating induced a temperature gradient, which gave rise to a surface tension and eventually thermal and liquid flows within the drop. This flow manifested as twin vortices, which after experimental and theoretical arguments was attributed to Marangoni convection. We present, here, the influence of surface wettability which was found to play a major role in the convective patterns. Moreover, heating location and power on both the Marangoni convection patterns and the evaporation kinetics of the drops..
43. Zhenying Wang, Daniel Orejon, K. Sefiane, Y. Takata, Vapor absorption phenomenon into sessile liquid desiccant droplets, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 843-850, 2018.01, This paper reveals the vapor absorption phenomena of liquid desiccant solution droplets on solid surfaces based on heat and mass transfer analyses. Vapor absorption is function of the pressure difference between the ambient air and the partial pressure of the vapor in the vicinity of the droplet liquid-gas interface. Due to the presence of salt ions (Li+, Br-) in the droplet, the vapor pressure at the droplet surface is significantly reduced, and hence vapor absorbs accordingly. Depending on the different ambient conditions, the droplet behavior differs. On hydrophilic glass substrate, the droplets spread slowly with monotonously decreasing contact angle and increasing contact radius. While on hydrophobic PTFE substrate, the droplets spread much less, and an “advancing stick-slip” phenomenon is observed at high ambient humidity. Different from water droplet, the solute concentration of the LiBr-H2O droplet will change along with time due to water absorption, which then causes a decrease in the vapor pressure difference. Therefore, the vapor absorption process will slow down due to the decreasing driving force, which corresponds with the observed droplet performance. Moreover, the volume expansion ratio, i.e., final volume to initial volume ratio, of the liquid desiccant droplets only depends on the ambient relative humidity, which is supported by the equilibrium relationship between the ambient air and the desiccant solution. Finally, droplets on hydrophilic glass substrates can reach equilibrium with the ambience faster than those on hydrophobic PTFE substrates, which is explained by the apparently shorter characteristic length for solute diffusion within droplets on hydrophilic substrates..
44. Biao Shen, Masayuki Yamada, Sumitomo Hidaka, Jiewei Liu, Junichiro Shiomi, Gustav Amberg, Minh Do-Quang, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces, Scientific reports, 10.1038/s41598-017-02163-8, 7, 1, 2017.12, For phase-change cooling schemes for electronics, quick activation of nucleate boiling helps safeguard the electronics components from thermal shocks associated with undesired surface superheating at boiling incipience, which is of great importance to the long-term system stability and reliability. Previous experimental studies show that bubble nucleation can occur surprisingly early on mixed-wettability surfaces. In this paper, we report unambiguous evidence that such unusual bubble generation at extremely low temperatures-even below the boiling point-is induced by a significant presence of incondensable gas retained by the hydrophobic surface, which exhibits exceptional stability even surviving extensive boiling deaeration. By means of high-speed imaging, it is revealed that the consequently gassy boiling leads to unique bubble behaviour that stands in sharp contrast with that of pure vapour bubbles. Such findings agree qualitatively well with numerical simulations based on a diffuse-interface method. Moreover, the simulations further demonstrate strong thermocapillary flows accompanying growing bubbles with considerable gas contents, which is associated with heat transfer enhancement on the biphilic surface in the low-superheat region..
45. Peng Zhang, Yota Maeda, Fengyong Lv, Yasuyuki Takata, Daniel Orejon, Enhanced Coalescence-Induced Droplet-Jumping on Nanostructured Superhydrophobic Surfaces in the Absence of Microstructures, ACS Applied Materials and Interfaces, 10.1021/acsami.7b09681, 9, 40, 35391-35403, 2017.10, Superhydrophobic surfaces are receiving increasing attention due to the enhanced condensation heat transfer, self-cleaning, and anti-icing properties by easing droplet self-removal. Despite the extensive research carried out on this topic, the presence or absence of microstructures on droplet adhesion during condensation has not been fully addressed yet. In this work we, therefore, study the condensation behavior on engineered superhydrophobic copper oxide surfaces with different structural finishes. More specifically, we investigate the coalescence-induced droplet-jumping performance on superhydrophobic surfaces with structures varying from the micro-to the nanoscale. The different structural roughness is possible due to the specific etching parameters adopted during the facile low-cost dual-scale fabrication process. A custom-built optical microscopy setup inside a temperature and relative humidity controlled environmental chamber was used for the experimental observations. By varying the structural roughness, from the micro-to the nanoscale, important differences on the number of droplets involved in the jumps, on the frequency of the jumps, and on the size distribution of the jumping droplets were found. In the absence of microstructures, we report an enhancement of the droplet-jumping performance of small droplets with sizes in the same order of magnitude as the microstructures. Microstructures induce further droplet adhesion, act as a structural barrier for the coalescence between droplets growing on the same microstructure, and cause the droplet angular deviation from the main surface normal. As a consequence, upon coalescence, there is a decrease in the net momentum in the out-of-plane direction, and the jump does not ensue. We demonstrate that the absence of microstructures has therefore a positive impact on the coalescence-induced droplet-jumping of micrometer droplets for antifogging, anti-icing, and condensation heat transfer applications..
46. Naoya Sakoda, Jiang Shiheng, Masamichi Kohno, Shigeru Koyama, Yukihiro Higashi, Yasuyuki Takata, Gaseous PVT Property Measurements of cis-1,3,3,3-Tetrafluoropropene, Journal of Chemical and Engineering Data, 10.1021/acs.jced.7b00263, 62, 7, 2178-2182, 2017.07, PVT properties in the vapor phase of cis-1,3,3,3-tetrafluoropropene (R1234ze(Z)) were measured by a multiple expansion method in the temperature range from 353 to 413 K and at pressures up to 2.7 MPa. Thirty data along four isotherms are obtained in the temperatures between 353 and 413 K. The vapor pressures at the temperatures were also measured by adding a sample of R1234ze(Z) to a sample cell at the vapor-liquid equilibrium conditions. The uncertainties in temperature and pressure measurements are estimated to be within 6 mK and 0.3 kPa, respectively. The expanded uncertainty in density measurement is estimated within no greater than 0.12% (k = 2). The obtained PVT properties and vapor pressures are compared with the existing equation of state..
47. Alexandros Askounis, Yutaku Kita, Masamichi Kohno, Yasuyuki Takata, Vasileios Koutsos, Khellil Sefiane, Influence of Local Heating on Marangoni Flows and Evaporation Kinetics of Pure Water Drops, Langmuir, 10.1021/acs.langmuir.7b00957, 33, 23, 5666-5674, 2017.06, The effect of localized heating on the evaporation of pure sessile water drops was probed experimentally by a combination of infrared thermography and optical imaging. In particular, we studied the effect of three different heating powers and two different locations, directly below the center and edge of the drop. In all cases, four distinct stages were identified according to the emerging thermal patterns. In particular, depending on heating location, recirculating vortices emerge that either remain pinned or move azimuthally within the drop. Eventually, these vortices oscillate in different modes depending on heating location. Infrared data allowed extraction of temperature distribution on each drop surface. In turn, the flow velocity in each case was calculated and was found to be higher for edge heating, due to the one-directional nature of the heating. Additionally, calculation of the dimensionless Marangoni and Rayleigh numbers yielded the prevalence of Marangoni convection. Heating the water drops also affected the evaporation kinetics by promoting the "stick-slip" regime. Moreover, both the total number of depinning events and the pinning strength were found to be highly dependent on heating location. Lastly, we report a higher than predicted relationship between evaporation rate and heating temperature, due to the added influence of the recirculating flows on temperature distribution and hence evaporation flux..
48. Yasuo Koizumi, Masanori Monde, Yasuyuki Takata, Outline of Boiling Phenomena and Heat Transfer Characteristics, Boiling Research and Advances, 10.1016/B978-0-08-101010-5.00001-4, 1-11, 2017.06, The objective of this book is to collect research works achieved during recent 20 years in the progress of boiling research in Japan. This book is edited for a person who has some experience or basic knowledge on boiling heat transfer. The fundamental outlines of pool nucleate boiling and flow boiling, and also new trend that boiling is considered to be a basic science that can be studied by numerical simulation or from the aspect of microscopic physics are briefly covered..
49. Tomohiko Yamaguchi, Gyoko Nagayama, Takaharu Tsuruta, Yuyan Jiang, Shigeo Maruyama, Kunito Okuyama, Yasushi Saito, Koichi Suzuki, Manabu Tange, Ichiro Ueno, Tomohiro Osawa, Yasusuke Hattori, Takahito Saiki, Jun Ando, Kazuna Horiuchi, Yusuke Koiwa, Hitoshi Asano, Kazuhisa Yuki, Yasuyuki Takata, Yoshiyuki Abe, Raffaele Savino, Serizawa Yoshihiro, Hidetoshi Ohkubo, Yutaka Abe, Shinpei Saitho, Masahiro Furuya, Satoru Momoki, Chieko Kondou, Shigeru Koyama, Mamoru Ozawa, Topics on Boiling
From Fundamentals to Applications, Boiling Research and Advances, 10.1016/B978-0-08-101010-5.00006-3, 443-777, 2017.06, This chapter deals with the various topics on boiling with regard to aspects of the fundamentals and applications to introduce the development of each author's research in recent decades. The first four sections investigate the physics of boiling as phase change phenomena, including thermodynamic phase equilibrium state (Section 6.1), molecular dynamics of phase change (Section 6.2), computational analysis of boiling in micro-nano scale (Section 6.3), and transient boiling under rapid heating (Section 6.4). Section 6.5 deals with two-phase distribution measurement using neuron radiography. The following three sections then examine a specific boiling regime during highly subcooled boiling, called microbubble emission boiling (MEB). Each section treats the overall characteristics of MEB (Section 6.6), the occurrence conditions of MEB (Section 6.7), and vapor collapses in subcooled liquid related to MEB (Section 6.8). The next four sections are devoted to heat transfer augmentation with various techniques: thermal spray coating (Section 6.9), porous media (Section 6.10), patterned wettability refinement (Section 6.11), and self-rewetting fluid (Section 6.12). The last seven sections describe topics on applications of boiling. Sections 6.13 and 6.14 introduce boiling research in steel industries. Sections 6.15 and 6.16 explore vapor explosion. Boiling of refrigerant is discussed with heat pump systems in Section 6.17 and with automobile air conditioners in Section 6.18. Boiling related to emergency cooling core systems is considered in Section 6.19..
50. Elin Yusibani, Yasuyuki Takata, Zaki Suud, Dwi Irwanto, The prediction of helium gas viscosity under high pressure and high temperature with the Chapman-Enskog solution and excess viscosity, Journal of Physics: Conference Series, 10.1088/1742-6596/799/1/012008, 799, 1, 2017.02, The purpose of this work is to predict a helium gas viscosity under high pressure and high temperature for practical industrial uses. The suitable force constants and a collision integral for the Chapman-Enskog solution to estimate viscosity in the limit of zero density were recommended by the present author. At high density, modification of the Arp and McCarty extrapolation equation for excess viscosity was applied. A combination of the Chapman-Enskog solution and modification of the Arp and McCarty excess viscosity gives an estimation of helium gas viscosity within 2 to 5 % deviation from the existing experimental data under high-temperature and high-pressure region..
51. Biao Shen, Bambang Joko Suroto, Sana Hirabayashi, Masayuki Yamada, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Bubble activation from a hydrophobic spot at “negative“ surface superheats in subcooled boiling, Applied Thermal Engineering, 10.1016/j.applthermaleng.2014.10.054, 88, 2017.01, We present experimental results on the controlled bubble generation from a single PTFE (polytetrafluoroethylene) spot-with diameter varying from 2mm to 6mm-deposited on a flat polished copper surface that was submersed in subcooled pure water. The static contact angle of the PTFE coating was measured to be over 120°, which conveniently produced a clear contrast with the copper substrate in terms of wettability that ensured controlled bubble nucleation. By making use of a high-speed camera, statistical details about the bubble formation that include the departure frequency and diameter have been obtained at various surface temperatures. An interesting observation was made of repeated cycles of bubble nucleation and detachment at nominally negative surface superheats (i.e., the wall temperature being below the saturation temperature at the system pressure), which featured particularly long bubble growth time and seemingly no waiting time. The vertical temperature distribution inside the bubble, which was measured by a micro-thermocouple of about 250μm in diameter, suggests a relatively stable bubble composition of water vapor and dissolved air. A heat-pipe analogy was drawn to describe the internal heat transfer mechanism of bubble growth on a mixed wettability surface under subcooled conditions..
52. Nitesh Das, Yasuyuki Takata, Masamichi Kohno, Sivasankaran Harish, Effect of carbon nano inclusion dimensionality on the melting of phase change nanocomposites in vertical shell-tube thermal energy storage unit, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2017.05.101, 113, 423-431, 2017.01, In the present work, we numerically investigate the melting phenomena of carbon based nanocomposites in vertically oriented shell-tube latent heat thermal energy storage system. Organic alkane n-eicosane was considered as the phase change material and carbon allotropes as the nano fillers to enhance the thermal conductivity of n-alkane. The effect of different carbon allotropes like nanodiamond (spherical), single-walled carbon nanotubes (one-dimensional) and graphene nanoplatelets (two-dimensional) were considered. Thermal conductivity of nanocomposites was modeled using effective medium based formulation taking the interfacial thermal boundary resistance between nanomaterial and the surrounding host matrix into account. Numerical results show that spherical nano inclusions do not enhance the melting rate due to limited enhancement in the thermal conductivity of nanocomposites. However, the inclusion of one-dimensional and two-dimensional nanostructures shorten the melting time by ∼15% and ∼25% respectively at 1 vol% loading as a result of higher thermal conductivity enhancement..
53. Hongbin He, Kento Furusato, Masayuki Yamada, Biao Shen, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Efficiency enhancement of a loop thermosyphon on a mixed-wettability evaporator surface, Applied Thermal Engineering, 10.1016/j.applthermaleng.2017.05.145, 123, 1245-1254, 2017.01, This study presents an experimental investigation of the heat transfer performance of a two-phase loop thermosyphon with an enhanced mixed-wettability evaporator surface at sub-atmospheric pressures. For central-processing-unit (CPU) cooling applications, a lowering of the saturation temperature (pressure) is essential when water is used as the working fluid. Compared with copper mirror surfaces, up to over 100% enhancement of high heat transfer coefficient (HTC) was observed using surfaces with spotted wettability patterns, which consists of hydrophobic spots with contact angle ranged from 145° to 150°. The results revealed that the boiling behaviors changed drastically with the application of hydrophobic spots coating by artificially increasing the nucleation site density. Parametric tests with a variety of operating conditions, including different filling ratios, condenser temperatures, and heat loads revealed the minimum thermal resistance (i.e., the optimum thermosyphon performance) to be 0.03 K/W on the boiling side..
54. Nitesh Das, Masamichi Kohno, Yasuyuki Takata, Dhiraj V. Patil, Sivasankaran Harish, Enhanced melting behavior of carbon based phase change nanocomposites in horizontally oriented latent heat thermal energy storage system, Applied Thermal Engineering, 10.1016/j.applthermaleng.2017.07.084, 125, 880-890, 2017.01, Present study describes the numerical analysis of the melting process of phase change nanocomposites in a horizontally oriented shell-tube latent heat thermal energy storage system. Organic alkane n-eicosane is considered as the pristine phase change material. The influence of different carbon based allotropes in enhancing the thermal conductivity of n-eicosane is considered in this work. To enhance the thermal conductivity of organic alkane, highly conductive carbon nano inclusions of various dimensionalities such as spherical (nanodiamond), one dimensional (single-walled carbon nanotube) and two-dimensional (graphene nanoplatelets) structures were considered. Effective thermal conductivity of such nanocomposites are theoretically modeled based on effective medium formulation considering the influence of interfacial thermal boundary resistance between the nanostructure and the surrounding host matrix into account. Numerical results show that the interfacial thermal boundary resistance and dimensionality of the nano inclusion significantly affects the thermal conductivity enhancement of such nanocomposites. For a fixed nanomaterial loading of 1 vol%, spherical nanoparticle inclusions enhance the melting rate only by ∼2%. The inclusion of 1 vol% loading of single-walled carbon nanotube and graphene nanoplatelets increases the melting rate by 27% and 40% respectively due to significant thermal conductivity enhancement of the nanocomposite compared to that of pure organic alkane..
55. Harish Sivasankaran, Daniel Mantecon Orejon, Yasuyuki Takata, Masamichi Kohno, Enhanced thermal conductivity of phase change nanocomposite in solid and liquid state with various carbon nano inclusions, Applied Thermal Engineering, 10.1016/j.applthermaleng.2016.10.109, 114, 1240-1246, 2017.01, We report contrasting enhancement in the solid state and liquid state thermal conductivity of phase change nanocomposite seeded with various carbon nano inclusions. Phase change nanocomposites were prepared using n-Dodecanoic acid as the host matrix. Single-walled carbon nanohorns, multi-walled carbon nanotubes and few-layer graphene nanosheets were considered as the nano inclusions. Thermal conductivity measurements were carried out using a custom built transient hotwire technique. The thermal conductivity enhancement significantly depends on the shape and aspect ratio of the nano inclusions. Maximum thermal conductivity enhancement was obtained in the presence of graphene nanosheets as the nanofiller candidate followed by carbon nanotubes and carbon nanohorns. The thermal conductivity enhancement was significantly higher in the solid state than the liquid state of the material for all the nano composites. Thermal conductivity enhancement results were compared with the effective medium theory calculations and Yamada-Ota model calculations considering the role of interfacial thermal resistance between the nanomaterial and the surrounding host matrix. The model calculations show that that the interfacial thermal resistance significantly limits the thermal conductivity enhancement in the liquid state compared to the solid state. The model calculations also show that interfacial thermal resistance is an order of magnitude higher at the solid-liquid interface compared to that of solid-solid interface which leads to a contrasting thermal conductivity enhancement in liquid and solid state of the nanocomposites..
56. M. Yamada, B. Shen, T. Imamura, S. Hidaka, M. Kohno, K. Takahashi, Y. Takata, Enhancement of boiling heat transfer under sub-atmospheric pressures using biphilic surfaces, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2017.08.078, 115, 753-762, 2017.01, Surface wettability of a heating surface is one of the most important factors affecting boiling performance. While a biphilic surface (with juxtaposed hydrophilic and hydrophobic regions) is known as a promising technique to enhance water pool boiling at the atmospheric pressure, there is no research regarding its potential for sub-atmospheric applications. In the present study, we have investigated the characteristics of pool nucleate boiling on biphilic surfaces at sub-atmospheric pressures. Biphilic surfaces were made by applying Ni-TFEO (tetrafluoroethylene oligomer) electroplating (with a contact angle of about 140°) on a copper surface. The heat transfer performance of various biphilic surfaces (with different hydrophobic spot diameters and pitches) were measured in the pressure range from atmospheric to 6.9 kPa. At a pressure of 14.0 kPa, the wall superheat at the onset of nucleate boiling was reduced by 12 K on a biphilic surface compared with a mirror-finished copper surface. The experiment with three different biphilic patterns revealed that smaller pitch and diameter of the hydrophobic spots were favorable to heat transfer at 14.0 kPa. The enhancement of HTC over Kutateladze's correlation reached 270%. A sharp transition from continuous to intermittent boiling, resulting in large deterioration of HTC, was observed on a biphilic surface at a much lower pressure than that on a copper surface. Boiling performance was less affected by the pressure level above the transition pressure..
57. Shen Yan, Cheng Dong, Tingting Miao, Wei Wang, Weigang Ma, Xing Zhang, Masamichi Kohno, Yasuyuki Takata, Long delay time study of thermal transport and thermal stress in thin Pt film-glass substrate system by time-domain thermoreflectance measurements, Applied Thermal Engineering, 10.1016/j.applthermaleng.2016.08.110, 111, 1433-1440, 2017.01, Solid state thermoelectric devices are desirable for various sustainable applications. Most of these thin film devices are multilayered structures which requires thorough understanding of thermal transport and thermal stress in order to solve thermal issues. In this paper the experimental technology as well as theoretical model of long delay time pump-probe study with four different illumination configurations have been developed to comprehensively characterize the thermal transport and thermal stress of thin film, substrate and the interface. Furthermore, 94-nm-thick Pt film-glass substrate system has been studied by applying time-domain thermoreflectance measurements under four illumination configurations with high signal quality. The obtained time-dependent temperature signal is superposed by the effects of multilayered thermal transport and thermal stress spontaneously, and the corresponding theoretical predictions match well with the experimental data in the whole delay time range. The determined thermal conductivity of the Pt film shows significant size effect..
58. Yoko Tomo, Koji Takahashi, Takashi Nishiyama, Tatsuya Ikuta, Yasuyuki Takata, Nanobubble nucleation studied using Fresnel fringes in liquid cell electron microscopy, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2017.01.013, 108, 1460-1465, 2017.01, Liquid cell electron microscopy is a useful technique for the observation of chemical, biological, and mechanical processes in liquids at nanometer-scale resolution. This study investigated the generation and growth of nanobubbles using the Fresnel fringe method, which enabled us to determine the location of bubble interface; the nanobubbles were induced in the 600-nm-thick water sample in the cell, by the electron beam. Nucleation occurred first at the solid–liquid interface in the upstream side of electron beam, and this was followed by second-group nucleation at the downstream-side interface; all of the stable nucleations occurred on the solid surfaces. The size of the nucleated bubbles at the moment they became visible depended on the magnification used in the electron microscope, and a higher-energy density in the electron beam induced larger bubbles. The underlying mechanism was also considered in this study..
59. Daniel Orejon, Orest Shardt, Naga Siva Kumar Gunda, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, Sushanta K. Mitra, Simultaneous dropwise and filmwise condensation on hydrophilic microstructured surfaces, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2017.06.023, 114, 187-197, 2017.01, While wicking or spreading of a liquid through microstructures has been found to be promising for applications such as textiles, microelectronics or heat sinks, the effects of such structured surfaces on condensation phase change has received less attention. On a hydrophilic surface and for a fixed micropillar aspect ratio (height/diameter), the spacing between pillars is found to have a strong impact on the dynamics of condensation and on the final morphology of the condensate. In the case of micropillars with a large spacing between pillars, the condensate grows initially dropwise, and thereafter, as condensation develops, the condensate overcomes the pillars’ height flooding the substrate, and condensation continuous in a filmwise condensation (FWC) fashion. In contrast, filmwise condensation and the continuous nucleation, growth, and departure of drops at the pillars’ tops in a dropwise condensation (DWC) fashion occurs when the spacing between pillars is decreased. In this configuration, the geometry of the microstructures constrains the condensate between the pillars and rise of the condensate interface above the micropillars’ height is not thermodynamically favorable, while the top of the pillars act as nucleation sites. We refer to this latter condensation behavior as simultaneous dropwise/filmwise condensation. These observations were enabled by the excellent spatial and temporal resolution of Environmental Scanning Electron Microscopy. A heat transfer model is proposed to demonstrate the greater heat transfer performance of the simultaneous dropwise/filmwise condensation behavior on these surfaces when compared to solely filmwise condensation. The enhanced heat transfer is realizable due to the ability to maintain a thin film within the microstructures and to the active dropwise condensation at the micropillars’ tops. We report for the first time the occurrence of dropwise condensation on a completely hydrophilic wettability configuration without the assistance of a hydrophobic coating. Our findings pave the way to the development of microstructures for enhanced condensation heat transfer..
60. Yutaka Yamada, Alexandros Askounis, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, Khellil Sefiane, Thermal conductivity of liquid/carbon nanotube core-shell nanocomposites, Journal of Applied Physics, 10.1063/1.4973488, 121, 1, 2017.01, Hollow carbon nanotubes (CNTs) were impregnated with an ionic liquid, resulting in a composite core-shell nanostructure. Liquid infusion was verified by transmission electron microscopy and rigorous observations unveiled that the nanocomposite is stable, i.e., liquid did not evaporate owing to its low vapor pressure. A series of individual nanostructures were attached on T-type heat sensors and their thermal behavior was evaluated. The liquid core was found to reduce the thermal conductivity of the base structure, CNT, from ca. 28 W/mK to ca. 15 W/mK. These findings could contribute to a better understanding of nanoscale thermal science and potentially to applications such as nanodevice thermal management and thermoelectric devices..
61. Masahiro Narasaki, Haidong Wang, Yasuyuki Takata, Koji Takahashi, Influence of ion beam scattering on the electrical resistivity of platinum hot films, Microelectronic Engineering, 10.1016/j.mee.2016.09.008, 166, 15-18, 2016.12, Platinum hot films have been used as precise resistance thermometers to measure the thermal conductivities of carbon nanotubes and graphene. Assisted by focused ion beam (FIB) irradiation, the influence of defects on phonon transport have been examined. However, wide lateral ion beam scattering may affect the electrical properties of hot films and cause uncertainty. In this letter, the effect of FIB irradiation on the electrical resistivity of platinum hot films was evaluated. To investigate this effect qualitatively, electrical resistivity measurement and FIB irradiation were alternated while changing irradiation positions and doses. Irradiated ions were found to travel further than 25 μm away from the directly irradiated area, resulting in an increase of electrical resistivity of the film according to total accumulated dose. The number of scattered ions was found to depend on the irradiated surface. An empirical equation describing the relationship between electrical resistivity and assumed ion density in the hot films was proposed. The obtained results enable us to accurately estimate the thermal or electrical properties of nanomaterials using hot-film sensors combined with nanofabrication techniques using FIB..
62. Alexandros Askounis, Yutaka Yamada, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, Khellil Sefiane, On the linear dependence of a carbon nanofiber thermal conductivity on wall thickness, AIP Advances, 10.1063/1.4968831, 6, 11, 2016.11, Thermal transport in carbon nanofibers (CNFs) was thoroughly investigated. In particular, individual CNFs were suspended on T-type heat nanosensors and their thermal conductivity was measured over a range of temperatures. Unexpectedly, thermal conductivity was found to be dependent on CNF wall thickness and ranging between ca. 28 and 43 W/(m⋅K). Further investigation of the CNF walls with high resolution electron microscopy allowed us to propose a tentative description of how wall structure affects phonon heat transport inside CNFs. The lower thermal conductivities, compared to other CNTs, was attributed to unique CNF wall structure. Additionally, wall thickness is related to the conducting lattice length of each constituent graphene cone and comparable to the Umklapp length. Hence, as the wall thickness and thus lattice length increases there is a higher probability for phonon scattering to the next layer..
63. Yutaku Kita, Alexandros Askounis, Masamichi Kohno, Yasuyuki Takata, Jungho Kim, Khellil Sefiane, Induction of Marangoni convection in pure water drops, Applied Physics Letters, 10.1063/1.4966542, 109, 17, 2016.10, We report on experimental observations/visualization of thermocapillary or Marangoni flows in a pure water drop via infrared thermography. The Marangoni flows were induced by imposing a temperature gradient on the drop by locally heating the substrate directly below the center with a laser. Evidently, a temperature gradient along the liquid-air interface of ca. 2.5 °C was required for the Marangoni flows to be initiated as twin vortices and a subsequent gradient of ca. 1.5 °C to maintain them. The vortices exhibited an oscillatory behavior where they merged and split in order for the drop to compensate for the non-uniform heating and cooling. The origin of these patterns was identified by comparing the dimensionless Marangoni and Rayleigh numbers, which showed the dominance of the Marangoni convection. This fact was further supported by a second set of experiments where the same flow patterns were observed when the drop was inverted (pendant drop)..
64. Deendarlianto, Yasuyuki Takata, Masamichi Kohno, Sumitomo Hidaka, Takaaki Wakui, Akmal Irfan Majid, Hadiyan Yusuf Kuntoro, Indarto, Adhika Widyaparaga, The effects of the surface roughness on the dynamic behavior of the successive micrometric droplets impacting onto inclined hot surfaces, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2016.05.132, 101, 1217-1226, 2016.10, The effect of surface roughness on the dynamic behavior and the heat transfer phenomena of multiple successive micrometric water droplets impacting onto inclined heated solid surfaces has been studied experimentally. The inclination angles were 15°, 30°, and 45° from horizontal. The droplet diameters were 500 μm and 700 μm. The solid surface temperatures were decreased from 500 °C to 100 °C. The test material was stainless steel-grade 304 (SUS 304) with different surface roughness ranged from Ra 0.04 up to Ra 10. The droplet dynamics during the impacting onto inclined hot surfaces were investigated by using high-speed video camera. It was found that the surface roughness significantly affects quenching behavior. The higher the surface roughness, the lower the quenching time during the spray cooling. The solid-droplet contact time and the droplet spread diameter increase with the increase of surface roughness. Thus causing the decrease of the quenching time of inclined hot walls. Meanwhile, the critical heat flux and Leidenfrost temperatures are shown to be insensitive to the surface roughness..
65. Naoya Sakoda, Kiyoaki Onoue, T. Kuroki, K. Shinzato, Masamichi Kohno, M. Monde, Yasuyuki Takata, Transient temperature and pressure behavior of high-pressure 100 MPa hydrogen during discharge through orifices, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2016.06.114, 41, 38, 17169-17174, 2016.10, High-pressure hydrogen at a maximum of 100 MPa in a 1-L-volume vessel is discharged through 0.1-mm- and 0.2-mm-diameter orifices that imitate cracks, and the transient temperature and pressure behavior of the hydrogen in the vessel is presented. The hydrogen at the initial pressure of 100 MPa during its discharge through the ϕ 0.2-mm orifice reaches half of the initial pressure after 16 s, while it takes approximately nine times longer for the ϕ 0.1-mm orifice to reach half of the initial pressure. We theoretically calculate the transient temperature and pressure according to the fundamental equations based on the mass and energy conservations using an accurate equation of state for hydrogen. The actual flow rate through an orifice is generally smaller than the theoretically calculated flow rate because of the contraction flow. Therefore, in this study, we adopt the effective diameters of the orifices instead of the actual diameters, and from comparisons with the experimental pressure, we estimate them to be 0.6 and 0.9 of the actual diameters for the ϕ 0.1-mm and ϕ 0.2-mm orifices, respectively. We use a functional form with a time constant for the heat transfer coefficient to represent the transient temperature behavior, and we describe the time dependence of the heat transfer coefficient. The results show that the calculated temperature and pressure are in good agreement with the experimental values obtained..
66. SIVASANKARAN HARISH, Yasuyuki Takata, Masamichi Kohno, Melting of graphene based phase change nanocomposites in vertical latent heat thermal energy storage unit, APPLIED THERMAL ENGINEERING, 10.1016/j.applthermaleng.2016.06.166, 107, 101-113, 2016.08.
67. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroki Ago, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Yasuyuki Takata, A general method of fabricating free-standing, monolayer graphene electronic device and its property characterization, Sensors and Actuators, A: Physical, 10.1016/j.sna.2016.05.002, 247, 24-29, 2016.08, We demonstrate a general process for fabricating graphene nanoelectronic devices that have next several features: free-standing, micrometer-sized monolayer graphene with high quality, arbitrarily-shaped metallic electrodes or sensors. In contrast to the normal routes, a gas etching process is used to create a deep trench in silicon for suspending the whole graphene device in a much larger area. User-designed electrodes or sensors are fabricated on the suspended graphene at the same time for realizing multiple functions. In this work, a suspended gold nanofilm sensor is designed to measure the intrinsic electrical and thermal properties of graphene on site. The sensor serves as both electrode and precise resistance thermometer at the same time. By simply changing the metallic electrode shape and electrical circuit, the free-standing graphene can be made into different devices, such as single-molecule detector or nano-resonator. In order to test the robustness of graphene device, a high electrical current is applied to heat the graphene in vacuum until it breaks. The breakdown current density is measured to be 1.86 mA/μm. More importantly, this method is not only limited to graphene, but also can be applied to any other two-dimensional materials..
68. Shreyas Chavan, Hyeongyun Cha, Daniel Orejon, Kashif Nawaz, Nitish Singla, Yip Fun Yeung, Deokgeun Park, Dong Hoon Kang, Yujin Chang, Yasuyuki Takata, Nenad Miljkovic, Heat Transfer through a Condensate Droplet on Hydrophobic and Nanostructured Superhydrophobic Surfaces, Langmuir, 10.1021/acs.langmuir.6b01903, 32, 31, 7774-7787, 2016.08, Understanding the fundamental mechanisms governing vapor condensation on nonwetting surfaces is crucial to a wide range of energy and water applications. In this paper, we reconcile classical droplet growth modeling barriers by utilizing two-dimensional axisymmetric numerical simulations to study individual droplet heat transfer on nonwetting surfaces (90° < θa < 170°). Incorporation of an appropriate convective boundary condition at the liquid-vapor interface reveals that the majority of heat transfer occurs at the three phase contact line, where the local heat flux can be up to 4 orders of magnitude higher than at the droplet top. Droplet distribution theory is incorporated to show that previous modeling approaches underpredict the overall heat transfer by as much as 300% for dropwise and jumping-droplet condensation. To verify our simulation results, we study condensed water droplet growth using optical and environmental scanning electron microscopy on biphilic samples consisting of hydrophobic and nanostructured superhydrophobic regions, showing excellent agreement with the simulations for both constant base area and constant contact angle growth regimes. Our results demonstrate the importance of resolving local heat transfer effects for the fundamental understanding and high fidelity modeling of phase change heat transfer on nonwetting surfaces..
69. Nitesh Das, Yasuyuki Takata, Masamichi Kohno, Sivasankaran Harish, Melting of graphene based phase change nanocomposites in vertical latent heat thermal energy storage unit, Applied Thermal Engineering, 10.1016/j.applthermaleng.2016.06.166, 107, 101-113, 2016.08, The present study deals with the investigation of melting phenomena in single vertical shell-and-tube latent heat thermal energy storage unit. A two dimensional axi-symmetric computational fluid dynamics model based on the enthalpy-porosity method was developed to investigate the melting behaviour. Organic alkane n-eicosane and n-eicosane/graphene nanosheets with different volume fractions were considered as the phase change materials (PCMs). Water was considered as the heat transfer fluid (HTF) flowing inside the tube and the PCM is filled in the shell side of thermal energy storage unit. A variety of numerical simulations were performed for different heat transfer fluid inlet temperatures and varying loadings of graphene nanosheets. Numerical calculations show that higher inlet temperature of the heat transfer fluid decreases the melting time due to accelerated natural convection. We also show that the inclusion of graphene nanosheets significantly decreases the melting time due to the enhanced thermal conductivity of PCM. At 2 vol% graphene laoding, melting time reduces significantly by ∼41% when the HTF temperature is 60 °C and ∼37% when the HTF temperature is 70 °C..
70. Shreyas Chavan, OREJON DANIEL, Kashif Nawaz, Nitish Singla, Yip Fun Yeung, Deokgeun Park, Yujin Chang, Yasuyuki Takata, Nenad Miljkovic, Heat Transfer through a Condensate Droplet on Hydrophobic and Nanostructured Superhydrophobic Surfaces, Langmuir, 32, 7774-7787, 2016.07.
71. Daniel Attinger, Yasuyuki Takata, Selected Papers from the 12th International Conference on Nanochannels, Microchannels, and Minichannels, Heat Transfer Engineering, 10.1080/01457632.2015.1097623, 37, 11, 901-902, 2016.07.
72. Yutaka Yamada, Koji Takahashi, Yasuyuki Takata, Khellil Sefiane, Wettability on Inner and Outer Surface of Single Carbon Nanotubes, Langmuir, 10.1021/acs.langmuir.6b01366, 32, 28, 7064-7069, 2016.07, The surface wettability of a liquid on the inner and outer surface of single carbon nanotubes (CNTs) was experimentally investigated. Although these contact angles on both surfaces were previously studied separately, the available data are of limited help to elucidate the effect of curvature orientation (concave or convex) on wettability due to the difference in surface structure. Here, we report on the three-phase contact region and wettability on the outer surface of CNT during the dipping and withdrawing experiment of CNT into an ionic liquid. Furthermore, the wettability on the inner surface was measured using a liquid within the same CNT. Our results show that the contact angle on the outer surface of the CNT is larger than that on the flat surface and that on the inner surface is smaller than that on the flat one. These findings suggest that the surface curvature orientation has a noticeable effect on the contact angle at the nanoscale because both inner and outer surfaces expose the same graphite wall structure and the contact line tension will be negligible in this situation. The presented results are rationalized using the free energy balance of liquid on curved surfaces..
73. Daniel Orejon, Martin E.R. Shanahan, Yasuyuki Takata, Khellil Sefiane, Kinetics of Evaporation of Pinned Nanofluid Volatile Droplets at Subatmospheric Pressures, Langmuir, 10.1021/acs.langmuir.6b00753, 32, 23, 5812-5820, 2016.06, We examine the effects of nanoparticle addition at low concentration on the evaporation kinetics of droplets in the constant radius mode. The evaporative behavior of deionized water and Al2O3 nanoparticle laden water on an aluminum substrate was observed at atmospheric and at different subatmospheric pressures. The two fluids exhibit the same evaporative behavior, independent of the droplet volume or the subatmospheric pressure. Moreover, the linear relationship between evaporation rate and droplet radius, initially proposed by Picknett and Bexon nearly four decades ago for droplets evaporating in the constant radius mode, is satisfied for both liquids. In addition, we have established a unified correlation solely function of fluid properties that extends this relationship to any subatmospheric pressure and fluid tested. We conclude that the addition of a small quantity of nanoparticles to the base fluid does not modify the kinetics of evaporation for pinned volatile droplets..
74. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroki Ago, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Yasuyuki Takata, Simultaneous measurement of electrical and thermal conductivities of suspended monolayer graphene, Journal of Applied Physics, 10.1063/1.4954677, 119, 24, 2016.06, We measured both in-plane electrical and thermal properties of the same suspended monolayer graphene using a novel T-type sensor method. At room temperature, the values are about 240 000 Ω-1 m-1 and 2100 W m-1 K-1 for the electrical and thermal conductivities, respectively. Based on the Wiedemann-Franz law, the electrons have negligible contribution to the thermal conductivity of graphene, while the in-plane LA and TA modes phonons are the dominant heat carriers. In monolayer graphene, the absence of layer-layer and layer-substrate interactions enhances the contribution of long wave-length phonons to the heat transport and increases the thermal conductivity accordingly. The reported method and experimental data of suspended monolayer graphene are useful for understanding the basic physics and designing the future graphene electronic devices..
75. Alexandros Askounis, Yasuyuki Takata, Khellil Sefiane, Vasileios Koutsos, Martin E.R. Shanahan, "biodrop" Evaporation and Ring-Stain Deposits
The Significance of DNA Length, Langmuir, 10.1021/acs.langmuir.6b00038, 32, 17, 4361-4369, 2016.05, Small sessile drops of water containing either long or short strands of DNA ("biodrops") were deposited on silicon substrates and allowed to evaporate. Initially, the triple line (TL) of both types of droplet remained pinned but later receded. The TL recession mode continued at constant speed until almost the end of drop lifetime for the biodrops with short DNA strands, whereas those containing long DNA strands entered a regime of significantly lower TL recession. We propose a tentative explanation of our observations based on free energy barriers to unpinning and increases in the viscosity of the base liquid due to the presence of DNA molecules. In addition, the structure of DNA deposits after evaporation was investigated by AFM. DNA self-assembly in a series of perpendicular and parallel orientations was observed near the contact line for the long-strand DNA, while, with the short-stranded DNA, smoother ring-stains with some nanostructuring but no striations were evident. At the interior of the deposits, dendritic and faceted crystals were formed from short and long strands, respectively, due to diffusion and nucleation limited processes, respectively. We suggest that the above results related to the biodrop drying and nanostructuring are indicative of the importance of DNA length, i.e., longer DNA chains consisting of linearly bonded shorter, rod-like DNA strands..
76. Yuki Fukatani, Takaaki Wakui, Suhaila Hussain, Masamichi Kohno, Yasuyuki Takata, Khellil Sefiane, Jungho Kim, Effect of Hydrothermal Waves on Evaporation Distribution during Drop Evaporation, Heat Transfer Engineering, 10.1080/01457632.2015.1067103, 37, 7-8, 729-739, 2016.05, The objective of this study is to clarify physical mechanisms involved in the evaporation of small (a few microliters) sessile drops. We aim to understand the relation between local thermal information at the solid-liquid interface and overall evaporation. An infrared (IR) camera and a charge-coupled device (CCD) camera were used to determine the temperature and heat flux distribution at the solid-liquid interface and the profile of the evaporating drop, respectively. The temperature distribution at the solid-liquid interface was determined using a multilayer substrate consisting of a silicon wafer coated with a thin thermal insulator that is partially transparent to IR. The liquids used were water and FC-72. The evaporation rate of water drops was found to occur mostly at the contact line. However, the heat transfer distribution at the liquid-solid interface was relatively uniform, indicating the heat transferred from the wall must be transported within the drop to the contact line. The mechanisms by which this occurs have yet to be determined. In contrast, the evaporation rate of FC-72 drops where hydrothermal waves were present was found to be proportional to the liquid-vapor interface area rather than the circumference of the drop, indicating a more uniform distribution of evaporation..
77. Takashi Nishiyama, Koji Takahashi, Tatsuya Ikuta, Yutaka Yamada, Yasuyuki Takata, Hydrophilic Domains Enhance Nanobubble Stability, ChemPhysChem, 10.1002/cphc.201501181, 17, 10, 1500-1504, 2016.05, Highly stable nanoscale gas states at solid/liquid interfaces, referred to as nanobubbles, have been widely studied for over a decade. In this study, nanobubbles generated on a hydrophobic Teflon amorphous fluoroplastic thin film in the presence and absence of hydrophilic carbon domains are investigated by peak force quantitative nanomechanics. On the hydrophobic surface without hydrophilic domains, a small number of nanobubbles are generated and then rapidly decrease in size. On the hydrophobic surface with hydrophilic domains, the hydrophilic domains have a significant effect on the generation and stability of nanobubbles, with bubbles remaining on the surface for up to three days. Bigger, better bubbles: The enhancement of nanobubble generation and stability by the existence of hydrophilic domains on a surface is shown (see picture). Close to the Ti/Si boundary, many nanobubbles are generated on the relatively hydrophobic Si surface. The hydrophilic-hydrophobic combination is one of the key factors for nanobubble generation and stabilization..
78. Yoshinori Hamamoto, Yasuyuki Takata, Selected Papers from the International Symposium on Innovative Materials for Processes in Energy Systems 2013 (IMPRES2013)
Part II, Heat Transfer Engineering, 10.1080/01457632.2015.1067069, 37, 7-8, 684-685, 2016.05.
79. A. Widyaparaga, T. Hiromatsu, T. Koshimizu, D. Deendarlianto, Masamichi Kohno, Yasuyuki Takata, Thermoacoustic heat pumping direction alteration by variation of magnitude and phase difference of opposing acoustic waves, Applied Thermal Engineering, 10.1016/j.applthermaleng.2016.02.032, 101, 330-336, 2016.05, Thermoacoustic refrigeration utilizes the temperature changes that occur due to pressure oscillations within a sound wave to transport heat from one point to another and achieve cooling. As such, it neither requires complicated machinery nor hazardous or environmentally harmful refrigerants. By altering the acoustic field, it is possible to also alter the direction of heat pumping allowing a single device to be capable of functioning as a heater or cooler without addition of complicated machinery. We have constructed a thermoacoustic heat pump employing dual opposing acoustic drivers or speakers connected by a resonator tube and a regenerator formed by layers of steel mesh positioned at the centre of the resonator to investigate the alteration of the acoustic field due to the interaction of opposing travelling waves. The acoustic field was manipulated by changing the phase difference and magnitude difference between the waves generated by the acoustic drivers. Experimental results show that the acoustic power flow on both sides of the regenerator was altered thus resulting in a change in heat pumping direction along the regenerator. In addition, it was also observed that the heat pumping was also influenced by the changes in the standing wave component (SWC) and the travelling wave component (TWC)..
80. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Hiroki Ago, Yasuyuki Takata, A simple method for fabricating free-standing large area fluorinated single-layer graphene with size-tunable nanopores, Carbon, 10.1016/j.carbon.2015.12.070, 99, 564-570, 2016.04, As a solid-state membrane with only one-atom thickness, nano-porous graphene has attracted intense attention in many critical applications. Here, the key challenge is to suspend a single-layer graphene (SLG) and drill nanopores with precise dimensions. Here, we report a simple and reliable route for making suspended fluorinated SLG with size-tunable nanopores. Our method consists of two steps: 1. a free-standing SLG ribbon was created between two gold pads after deep dry etching of silicon substrate by xenon difluoride. The SLG was fluorinated by 5-13%. Superior to the normal wet etching method, the dry etching process is much simpler and results in less hole-defect and edge deformation. A large area fluorinated SLG can be suspended due to the sufficient etch depth. 2. a focused ion beam was introduced to drill nanopores in graphene with an initial diameter around 20 nm. Followed by an electron beam induced carbon deposition, the diameter of nanopore was gradually decreased to sub-10 nm. By changing the deposition time, the size of nanopore can be precisely controlled. High-cost transmission electron microscope is no longer needed. Our method provides a simple and effective way for preparing free-standing fluorinated SLG ribbon suitable for single-molecule detection..
81. El Sayed R. Negeed, M. Albeirutty, Sharaf F. Al-Sharif, S. Hidaka, Y. Takata, Dynamic Behavior of a Small Water Droplet Impact onto a Heated Hydrophilic Surface, Journal of Heat Transfer, 10.1115/1.4032147, 138, 4, 2016.04, The aim of this study is to investigate the influence of the surface wettability on the dynamic behavior of a water droplet impacting onto a heated surface made of stainless steel grade 304 (Sus304). The surface wettability is controlled by exposing the surfaces to plasma irradiation for different time periods (namely, 0.0, 10, 60, and 120 s). The experimental runs were carried out by spraying water droplets on the heated surface where the droplet diameter and velocity were independently controlled. The droplet behavior during the collision with the hot surface has been recorded with a high-speed video camera. By analyzing the experimental results, the effects of surface wettability, contact angle between impacting droplet and the hot surface, droplet velocity, droplet size, and surface superheat on the dynamic behavior of the water droplet impacting on the hot surface were investigated. Empirical correlations are presented describing the hydrodynamic characteristics of an individual droplet impinging onto the heated hydrophilic surfaces and concealing the affecting parameters in such process..
82. Yuki Fukatani, Daniel Orejon, Yutaku Kita, Yasuyuki Takata, Jungho Kim, Khellil Sefiane, Effect of ambient temperature and relative humidity on interfacial temperature during early stages of drop evaporation, Physical Review E, 10.1103/PhysRevE.93.043103, 93, 4, 2016.04, Understanding drop evaporation mechanisms is important for many industrial, biological, and other applications. Drops of organic solvents undergoing evaporation have been found to display distinct thermal patterns, which in turn depend on the physical properties of the liquid, the substrate, and ambient conditions. These patterns have been reported previously to be bulk patterns from the solid-liquid to the liquid-gas drop interface. In the present work the effect of ambient temperature and humidity during the first stage of evaporation, i.e., pinned contact line, is studied paying special attention to the thermal information retrieved at the liquid-gas interface through IR thermography. This is coupled with drop profile monitoring to experimentally investigate the effect of ambient temperature and relative humidity on the drop interfacial thermal patterns and the evaporation rate. Results indicate that self-generated thermal patterns are enhanced by an increase in ambient temperature and/or a decrease in humidity. The more active thermal patterns observed at high ambient temperatures are explained in light of a greater temperature difference generated between the apex and the edge of the drop due to greater evaporative cooling. On the other hand, the presence of water humidity in the atmosphere is found to decrease the temperature difference along the drop interface due to the heat of adsorption, absorption and/or that of condensation of water onto the ethanol drops. The control, i.e., enhancement or suppression, of these thermal patterns at the drop interface by means of ambient temperature and relative humidity is quantified and reported..
83. Tingting Miao, Weigang Ma, Shen Yan, Xing Zhang, Masamichi Kohno, Yasuyuki Takata, Yoshifumi Ikoma, Thermal transport and thermal stress in a molybdenum film-glass substrate system, Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, 10.1116/1.4941308, 34, 2, 2016.03, Three-dimensional integration with through-silicon vias is emerging as an approach for improving the performance of integrated circuits. Thermal transport and thermal stress in such designs currently limit their performance and reliability. In this study, the thermal dissipation and thermal stress in a 95.3-nm-thick molybdenum (Mo) film-glass substrate system were investigated using a picosecond laser pump-probe method with four different configurations. This allowed the thermal transport and the generation and propagation of coherent acoustic phonon waves in a Mo film-glass substrate system to be comprehensively studied for the first time. The universality of the superposition model previously proposed for a platinum film on a glass substrate was verified using the present Mo film-glass substrate system from the close agreement between experimental data and theoretical predictions. The thermal transport in the Mo film and the coherent acoustic phonon wave propagation in the Mo film and glass substrate, i.e., thermal diffusivity and longitudinal sound velocity, respectively, were also studied..
84. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Hiroki Ago, Yasuyuki Takata, In-situ measurement of the heat transport in defect-engineered free-standing single-layer graphene, Scientific reports, 10.1038/srep21823, 6, 2016.02, Utilizing nanomachining technologies, it is possible to manipulate the heat transport in graphene by introducing different defects. However, due to the difficulty in suspending large-area single-layer graphene (SLG) and limited temperature sensitivity of the present probing methods, the correlation between the defects and thermal conductivity of SLG is still unclear. In this work, we developed a new method for fabricating micro-sized suspended SLG. Subsequently, a focused ion beam (FIB) was used to create nanohole defects in SLG and tune the heat transport. The thermal conductivity of the same SLG before and after FIB radiation was measured using a novel T-type sensor method on site in a dual-beam system. The nanohole defects decreased the thermal conductivity by about 42%. It was found that the smaller width and edge scrolling also had significant restriction on the thermal conductivity of SLG. Based on the calculation results through a lattice dynamics theory, the increase of edge roughness and stronger scattering on long-wavelength acoustic phonons are the main reasons for the reduction in thermal conductivity. This work provides reliable data for understanding the heat transport in a defective SLG membrane, which could help on the future design of graphene-based electrothermal devices..
85. Negeed, E.-S.R., Albeirutty, M., Al-Sharif, S.F., Hidaka, S., Yasuyuki Takata, Dynamic Behavior of a Small Water Droplet Impact onto a Heated Hydrophilic Surface, Journal of Heat Transfer, 138, 4, 042901, 2016.01.
86. Daniel Orejon, Orest Shardt, Prashant R. Waghmare, Naga Siva Kumar Gunda, Yasuyuki Takata, Sushanta K. Mitra, Droplet migration during condensation on chemically patterned micropillars, RSC Advances, 10.1039/c6ra03862j, 6, 43, 36698-36704, 2016.01, We demonstrate the migration of small water droplets from the side wall of a micropillar onto its top surface during dropwise condensation without application of an external force. The observed droplet migration occurs due to the difference in wettability between the hydrophobic sides and hydrophilic top surfaces of the micropillars imposed by a novel fabrication process. The movement of condensate from the pillars' side walls onto their tops is suggested as a method for shifting condensate from a Wenzel to a Cassie-Baxter state to promote droplet detachment. In this communication, we also emphasize the use of combined surface texturing and wettability patterning to prompt the migration of condensate on pillars for the effective design of surfaces for high condensation heat transfer performance..
87. Hiroyuki Fukuda, Naoki Nakata, Hideo Kijima, Takashi Kuroki, Akio Fujibayashi, Yasuyuki Takata, Sumitomo Hidaka, Effects of surface conditions on spray cooling characteristics, isij international, 10.2355/isijinternational.ISIJINT-2015-609, 56, 4, 628-636, 2016.01, The influence of surface conditions such as scale thickness and surface roughness on water spray cooling and air jet cooling characteristics was investigated experimentally. SUS304 stainless steel with the thickness of 20 mm was used as the cooled sample. An artificial scale layer was formed on the sample surface by thermal-spraying using Al2O3 powder. The thickness of the Al2O3 layer was varied from 50 μm to 210 μm. A sample without an artificial scale layer was also studied; in this case, the surface was roughened by shot blasting up to 20 μmRa. As a result, the artificial scale layer showed a thermal resistance function in both water spray cooling and air jet cooling. In water spray cooling, the characteristics of which depend on surface temperature, the cooling rate during film boiling and the apparent quenching temperature at the interface increased with Al2O3 scale thickness. Surface roughness enhanced the cooling rate during film boiling and resulted in a higher quenching temperature in spray cooling. In air jet cooling, heat flux increases with surface roughness, but this tendency can be seen only with larger flow rates. Surface roughness has a much stronger influence on heat flux in water spray cooling, even though the average heat flux is not as large. In this research, the heat flux during impingement of water droplets was estimated to be much higher than that in air jet cooling. This is thought to explain the difference in the influence of surface roughness on cooling characteristics with the two cooling methods..
88. Yutaka Yamada, Koji Takahashi, Tatsuya Ikuta, Takashi Nishiyama, Yasuyuki Takata, Wei Ma, Atsushi Takahara, Tuning Surface Wettability at the Submicron-Scale
Effect of Focused Ion Beam Irradiation on a Self-Assembled Monolayer, Journal of Physical Chemistry C, 10.1021/acs.jpcc.5b09019, 120, 1, 274-280, 2016.01, Realizing surface wettability tuning at the submicron-scale resolution is expected to enable the fabrication of micro/nano-structured fluidic devices and is particularly important in nanobiotechnology and high-resolution printing. Herein, we propose an approach to modify the wettability of self-assembled monolayer surfaces using focused ion beam (FIB) irradiation. The contact angle of the irradiated region changed from hydrophobic to hydrophilic by increasing the ion dosage. The chemical composition and associated depth profile of the sample surfaces were analyzed by glow discharge-optical emission spectroscopy. The results indicated that the content of fluorine at the surface decreased after FIB irradiation of the samples. A submicron-scale hydrophobic-hydrophilic hybrid surface was then fabricated by forming hydrophilic dots with diameters of ∼110 nm on a hydrophobic surface by FIB irradiation. The difference in wettability of the hydrophobic and hydrophilic areas on the surface was confirmed by microscale condensation and evaporation experiments. Condensed droplets with diameters of ∼300 nm appeared on the surface according to the fabricated pattern, thus suggesting that condensation preferentially occurred on the hydrophilic dots than on the hydrophobic surface. Furthermore, tiny droplets remained on the hydrophilic dots following evaporation of the larger droplets. The current approach provides a means to control wettability-driven phenomena..
89. N. Sakoda, T. Hisatsugu, K. Furusato, K. Shinzato, M. Kohno, Y. Takata, Viscosity measurements of hydrogen at high temperatures up to 573 K by a curved vibrating wire method, Journal of Chemical Thermodynamics, 10.1016/j.jct.2015.04.028, 89, 22-26, 2015.10, The viscosities of hydrogen were measured at temperatures of (296 to 573) K and at pressures up to 0.7 MPa by the vibrating wire method. In this study, a tungsten wire 50 μm in diameter and 24 mm in length is bent into semicircular form. The direction of the vibrating motion is fixed using the curved wire, and a more compact sample vessel can be used than in a traditional straight vibrating wire method requiring weight for the tension in the wire. Alternating voltages with different frequencies were supplied to the curved wire, which was set between samarium cobalt magnets. The generated induced voltages depending on the supplied frequencies were measured by a lock-in amplifier, and the resonant curve was obtained. The resonant frequency and half-width of the resonant curve were determined by curve fitting. The wire's effective diameter and internal friction coefficient, which represents the damping from the wire material and the magnetic force, are very important parameters for evaluating the viscosities, and they were precisely calibrated by measuring helium and nitrogen as reference fluids. Finally, the viscosities of hydrogen were obtained with an uncertainty of 1.4% (k = 2)..
90. Biao Shen, Bambang Joko Suroto, Sana Hirabayashi, Masayuki Yamada, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Bubble activation from a hydrophobic spot at “negative” surface superheats in subcooled boiling, Applied Thermal Engineering, 88, 230-239, 2015.09.
91. 大尾 岳史, Li H.-W., Gondo T., Miyazaki H., Ikuta T., 西山 貴史, 髙橋 厚史, 高田 保之, LYTH STEPHEN, 佐々木 一成, Dynamic Gas Environmental System Development for In-Situ Real-time SEM Imaging Under Atmospheric Pressure, SCIENTIFIC REPORTS, 21, S3, 1701-1702, 2015.08.
92. Takeshi Daio, Thomas Bayer, Koji Takahashi, Yasuyuki Takata, Kazunari Sasaki, In-Situ ESEM and EELS Observation of Water Uptake and Ice Formation in Multilayer Graphene Oxide, Scientific Reports, 5, 2015.07.
93. Sivasankaran Harish, Daniel Orejon, Yasuyuki Takata, Masamichi Kohno, Thermal conductivity enhancement of lauric acid phase change nanocomposite with graphene nanoplatelets, Applied Thermal Engineering, 10.1016/j.applthermaleng.2015.01.056, 80, 205-211, 2015.04, In this work, we prepared lauric acid based phase change nanocomposites with chemically functionalized graphene nanoplatelets and measured its thermal conductivity using transient hot wire method. We show that inclusion of graphene nanoplatelets increases the thermal conductivity of phase change material by 230% at a loading of 1 vol%. Comparing the experimental results with the model calculations based on the effective medium theory suggests that graphene based nanocomposites outperforms those with carbon nanotubes or metal nanoparticles reported in the literature. High thermal conductivity, high aspect ratio and low thermal interface resistance at the graphene - host matrix interface makes it the most suitable nano filler candidate to enhance the thermal conductivity of low conductive materials. Differential scanning calorimetry study of the nanocomposites show that the phase change enthalpy and the melting temperature remains similar to that of pristine material, which makes graphene a promising candidate for thermal energy storage applications..
94. Weigang Ma, Tingting Miao, Xing Zhang, Masamichi Kohno, Yasuyuki Takata, Comprehensive Study of Thermal Transport and Coherent Acoustic-Phonon Wave Propagation in Thin Metal Film-Substrate by Applying Picosecond Laser Pump-Probe Method, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp512735k, 119, 9, 5152-5159, 2015.03.
95. Weigang Ma, Tingting Miao, Xing Zhang, Masamichi Kohno, Yasuyuki Takata, Comprehensive study of thermal transport and coherent acoustic-phonon wave propagation in thin metal film - Substrate by applying picosecond laser pump - Probe method, Journal of Physical Chemistry C, 10.1021/jp512735k, 119, 9, 5152-5159, 2015.03, Three-dimensional integration with through silicon vias offers a promising solution for future technology nodes. However, the heat accumulation and thermal strain may seriously affect performance, leakage, and reliability of circuits. The cross-plane thermal transport, generation, and propagation of coherent acoustic-phonon wave in thin Pt film-glass substrate have been comprehensively studied by applying the picosecond laser pump-probe method with different configurations. Significantly different time-dependent reflectance signals have been obtained in different configurations and an effect superposition model is proposed to account for cross plane thermal transport inducing ipsi- and contralateral temperature change in thin Pt film, propagation of coherent acoustic-phonon wave in thin Pt film and in glass substrate. The corresponding theoretical predictions match well with the experimental data in the whole delay time range..
96. Takashi Nishiyama, 山田 寛, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, Metastable Nanobubbles at the Solid-Liquid Interface Due to Contact Angle Hysteresis, LANGMUIR, 10.1021/la5036322, 31, 3, 982-986, 2015.01.
97. Takashi Nishiyama, Yutaka Yamada, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, Metastable nanobubbles at the solid-liquid interface due to contact angle hysteresis, Langmuir, 10.1021/la5036322, 31, 3, 982-986, 2015.01, Nanobubbles exist at solid-liquid interfaces between pure water and hydrophobic surfaces with very high stability, lasting in certain cases up to several days. Not only semispherical but also other shapes, such as micropancakes, are known to exist at such interfaces. However, doubt has been raised as to whether or not the nanobubbles are gas-phase entities. In this study, surface nanobubbles at a pure water-highly ordered pyrolytic graphite (HOPG) interface were investigated by peak force quantitative nanomechanics (PF-QNM). Multiple isolated nanobubbles generated by the solvent-exchange method were present on the terraced areas, avoiding the steps of the HOPG surface. Adjacent nanobubbles coalesced and formed metastable nanobubbles. Coalescence was enhanced by the PF-QNM measurement. We determined that nanobubbles can exist for a long time because of nanoscale contact angle hysteresis at the water-HOPG interface. Moreover, the hydrophilic steps of HOPG were avoided during coalescence, providing evidence that the nanobubbles are truly gas phase..
98. Harish Sivasankaran, Daniel Mantecon Orejon, Yasuyuki Takata, Masamichi Kohno, Thermal conductivity enhancement of lauric acid phase change nanocomposite in solid and liquid state with single-walled carbon nanohorn inclusions, Thermochimica Acta, 10.1016/j.tca.2014.12.004, 600, 1-6, 2015.01, We prepared lauric acid based phase change nanocomposite embedded with chemically functionalized single-walled carbon nanohorns and measured its thermal properties. We report contrasting enhancements in thermal conductivity of such nanocomposites in the solid and liquid phase for the same loading of nanohorn inclusions. Maximum thermal conductivity enhancement in solid and liquid phase at 2 vol% is found to be ∼37 and ∼11%, respectively. The nanocomposites' thermal conductivity enhancement is compared with calculations of effective medium theory considering the role of interfacial thermal transport. Model calculations show that Kapitza resistance is an order of magnitude lower at the solid-solid interface compared to the solid-liquid interface. Differential scanning calorimetry study of the nanocomposites shows that the phase change temperature and enthalpy marginally increases to that of pristine material. Such a nanocomposite with enhanced thermal transport and phase change enthalpy makes it a promising candidate for thermal energy storage applications..
99. Takeshi Daio, Koji Takahashi, Yasuyuki Takata, Kazunari Sasaki, Dynamic Gas Environmental System Development for In-Situ Real-time SEM Imaging Under Atmospheric Pressure, Microscopy and Microanalysis, 21, S3, 1701-1702, 2015.
100. Yutaka Yamada, Koji Takahashi, Yasuyuki Takata, Study of condensation on hydrophobic surface with nanoscale hydrophilic regions, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 81, 823, 2015, Water condensation on a hydrophobic surface with nanoscale hydrophilic regions was investigated to reveal the condensation mechanism of submicron-scale droplets. This feature was found on the graphite step-terrace structured surface; step surfaces are more wettable relative to terrace surfaces, and it was precisely characterized using an atomic force microscope. Condensation experiments were conducted using an environmental scanning electron microscope and droplets were observed to line up on preferentially along the graphite steps. Observed droplets ranged from 150 to 300 nm in diameter and the droplet interval depends on the width of hydrophobic region. The heterogeneous nucleation theory was extended to consider attracted water molecules on hydrophilic step surface, which enable us to explain the current observed result under unsaturated condition. As a result, proposed theory shows qualitatively that narrower hydrophobic region induces short droplet interval. Our suggestion for design the hybrid hydrophilic-hydrophobic surface would enable the development of surface that will perform high heat transfer at dropwise condensation..
101. Yutaka Yamada, Takashi Nishiyama, Koji Takahashi, Yasuyuki Takata, Droplet Nucleation on a Well-Defined Hydrophilic-Hydrophobic Surface of 10 nm Order Resolution, LANGMUIR, 10.1021/la503615a, 30, 48, 14532-14537, 2014.12.
102. Yutaka Yamada, Tatsuya Ikuta, Takashi Nishiyama, Koji Takahashi, Yasuyuki Takata, Droplet nucleation on a well-defined hydrophilic-hydrophobic surface of 10 nm order resolution, Langmuir, 10.1021/la503615a, 30, 48, 14532-14537, 2014.12, Water condensation on a hybrid hydrophilic-hydrophobic surface was investigated to reveal nucleation mechanisms at the microscale. Focused ion beam (FIB) irradiation was used to change the wettability of the hydrophobic surface with 10 nm order spatial resolution. Condensation experiments were conducted using environmental scanning electron microscopy; droplets, with a minimum diameter of 800 nm, lined up on the FIB-irradiated hydrophilic lines. The heterogeneous nucleation theory was extended to consider the water molecules attracted to the hydrophilic area, thereby enabling explanation of the nucleation mechanism under unsaturated conditions. Our results showed that the effective surface coverage of the water molecules on the hydrophilic region was 0.1-1.1 at 0.0 °C and 560 Pa and was dependent on the width of the FIB-irradiated hydrophilic lines and hydrophobic area. The droplet nucleation mechanism unveiled in this work would enable the design of new surfaces with enhanced dropwise condensation heat transfer. (Figure Presented)..
103. OREJON DANIEL, Khellil Sefiane, Yasuyuki Takata, Effect of ambient pressure on Leidenfrost temperature, PHYSICAL REVIEW E, 10.1103/PhysRevE.90.053012, 90, 5, 2014.11.
104. Daniel Orejon, Khellil Sefiane, Yasuyuki Takata, Effect of ambient pressure on Leidenfrost temperature, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.90.053012, 90, 5, 2014.11, The accurate prediction and control of the interaction of liquids with hot surfaces is paramount in numerous areas, including cooling applications. We present results illustrating the effect of ambient pressure on the temperature required for a droplet to levitate over a hot surface, i.e., the Leidenfrost temperature. In the present study the dependence of wetting and levitating temperatures on ambient pressure in a range of subatmospheric pressures is reported. Experimental data indicate that the Leidenfrost temperature decreases with decreasing pressure at subatmospheric pressures. A physical approach for the dependence of Leidenfrost temperature on ambient pressure, based on an analogy with saturation pressure dependence, is proposed. Furthermore, previous literature data for pressures above atmospheric are also included in the analysis to support and validate the proposed approach. In addition, the effect of substrate material, substrate roughness, and type of fluid on the Leidenfrost temperature is discussed..
105. Bidyut Baran Saha, Yasuyuki Takata, S. Srinivasa Murthy, Special issue
Selected papers from the International Symposium on Innovative Materials for Processes in Energy Systems 2013 (IMPRES2013), Applied Thermal Engineering, 10.1016/j.applthermaleng.2014.09.072, 72, 2, 151-152, 2014.11.
106. Ryosuke Nagahisa, Daiki Kuriya, Hidetaka Marumatsu, Yasuyuki Takata, Kuniyasu Ogawa, Kohei Ito, Measurement System for Solubility and Self-Diffusivity of Hydrogen Gas Dissolved in Polymer Electrolyte Membrane, ECS Digital Library, 10.1149/2.0881410jes, volume 161, issue 10, F1070-F1074, 2014.07.
107. N. Sakoda, R. Kumagai, R. Ishida, K. Shinzato, M. Kohno, Y. Takata, Vacuum generation by hydrogen permeation to atmosphere through austenitic and nickel-base-alloy vessel walls at temperatures from 573 K to 773 K, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2014.05.031, 39, 21, 11316-11320, 2014.07, The permeation of hydrogen through metals is of great concern in hydrogen containment systems. In this study, hydrogen contained in seamless coiled tube vessels made of SUS 316L and Inconel 625 permeated the vessel walls at temperatures from 573 K to 773 K, and the decreasing interior pressure of the vessels was monitored for an extended period to characterize the behavior of the pressure change. It was found that the pressure became lower than the surrounding atmospheric pressure, and the vessels reached a vacuum. Hydrogen permeabilities through SUS 316L and Inconel 625 were determined from the pressure drop measurements. In order to ensure the reliability of the measurements, the permeabilities were also determined with a gas chromatograph that measured the concentration of hydrogen completely permeating the vessel wall. The permeabilities obtained with the two methods were in good agreement with each other. The pressure drop behavior was compared to, and found to be consistent with, theoretical calculations performed using the obtained permeabilities based on Fick's law of diffusion..
108. Sivasankaran Harish, Mitsuru Tabara, Yoshifumi Ikoma, Zenji Horita, Yasuyuki Takata, David Cahill, Masamichi Kohno, Thermal conductivity reduction of crystalline silicon by high-pressure torsion, NANOSCALE RESEARCH LETTERS, 10.1186/1556-276X-9-326, 9, 2014.06.
109. Tingting Miao, Weigang Ma, Xing Zhang, Keisuke Kubo, Masamichi Kohno, Yasuyuki Takata, Tatsuya Ikuta, Koji Takahashi, Study on the Cross Plane Thermal Transport of Polycrystalline Molybdenum Nanofilms by Applying Picosecond Laser Transient Thermoreflectance Method, Journal of Nanomaterials, Article ID 578758, 2014.06.
110. Huaiyu Shao, Weigang Ma, Masamichi Kohno, Yasuyuki Takata, Gongbiao XIn, Shigenri Fujikawa, Masaaki Sadakiyo, BISHOP SEAN, Xingguo Li, Hydrogen storage and thermal conductivity properties of Mg-based materials with different structures, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 10.1016/j.lihydene.2014.02.063, 39, 18, 9893-9898, 2014.06.
111. Huaiyu Shao, Weigang Ma, Masamichi Kohno, Yasuyuki Takata, Gongbiao Xin, Shigenori Fujikawa, Sayoko Fujino, Sean Bishop, Xingguo Li, Hydrogen storage and thermal conductivity properties of Mg-based materials with different structures, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2014.02.063, 39, 18, 9893-9898, 2014.06, Mg-based hydrogen storage materials can be very promising candidates for stationary energy storage application due to the high energy density and low cost of Mg. Hydrogen storage kinetics and thermal conductivity are two important factors for the material development for this kind of application. Here we studied several types of Mg-based materials with different structure-micrometer scale Mg powders, Mg nanoparticles, single crystal Mg, nanocrystalline Mg 50Co50 BCC alloy and Mg thin film samples. It seems the Mg materials with good kinetics usually are the ones with nanostructure and tend to show poor thermal conductivity due to electron/phonon scattering resulting from more interfaces and boundaries in nanomaterials. Based on this work, good crystallinity Mg phase incorporated in carbon nano framework could be one promising option for energy storage..
112. El-Sayed R. Negeed, M. Albeiruttya, Yasuyuki Takata, Dynamic behavior of micrometric single water droplets impacting onto heated surfaces with TiO2 hydrophilic coating, INTERNATIONAL JOURNAL OF THERMAL SCIENCES, 10.1016/j.ijthermalsci.2013.12.011, 79, 1-17, 2014.05.
113. El Sayed R. Negeed, M. Albeirutty, Yasuyuki Takata, Dynamic behavior of micrometric single water droplets impacting onto heated surfaces with TiO2 hydrophilic coating, International Journal of Thermal Sciences, 10.1016/j.ijthermalsci.2013.12.011, 79, 1-17, 2014.05, Dynamic behavior of micrometric single water droplets impacting onto heated surfaces with and without superhydrophilic coating is investigated using a high-speed video camera in this research study. Superhydrophilic surface coating, SHS, is achieved by coating the surface with Titanium dioxide, TiO 2, and by exposing the surface to ultraviolet, UV. Mirror heat transfer surfaces of different metals have been considered. The experimental runs are carried out by spraying single water droplets onto heated surfaces where, the droplet diameter and velocity were independently controlled. The droplet behavior during the collision with the hot surface has been observed with the high-speed video camera. By analyzing the experimental results and comparison between the present results and the results due to other investigators, the effects of surface wettability, thermal properties of the heat transfer surface, droplet velocity, droplet size and surface superheat on the dynamic behavior of micrometric single water droplets impacting onto the heated surfaces were investigated. Empirical correlations are presented describing the hydrodynamic characteristics of an individual droplet impinging onto the heated surfaces, and concealing the affecting parameters in such process..
114. Deendarlianto, Yasuyuki Takata, Sumitomo Hidaka, Indarto, Adhika Widyaparaga, Samsul Kamal, Purnomo, Masamichi Kohno, Effect of static contact angle on the droplet dynamics during the evaporation of a water droplet on the hot walls, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 10.1016/j.ijheatmasstransfer.2013.12.066, 71, 691-705, 2014.04.
115. Deendarlianto, Yasuyuki Takata, Sumitomo Hidaka, Indarto, Adhika Widyaparaga, Samsul Kamal, Purnomo, Masamichi Kohno, Effect of static contact angle on the droplet dynamics during the evaporation of a water droplet on the hot walls, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2013.12.066, 71, 691-705, 2014.04, The effect of surface wettability on the collision dynamics and heat transfer phenomena of a single water droplet impacting upon a heated solid surface has been studied experimentally. To modify the surface wettability, two modules of stainless steel coated by TiO2 were employed. The first module was induced by ultraviolet irradiation to produce the hydrophilic surface, while the second one was not. The diameter and the depth of coating surface were 30 mm and 200 nm, respectively. The droplet size was varied from 1.90 to 2.90 mm and substrate temperature raised up to 340 C. The interaction of an impact water droplet with a heated solid surface was investigated using a high-speed video camera. As a result, it was found that; (1) in the lower surface temperature region the evaporation time decreases as the static contact angle decreases, (2) the wetting limit temperature decreases with the increase of static contact angle, (3) the ultraviolet irradiation on the TiO2 surface does not change the qualitative behavior of the evolution of wetting diameters, and (4) the maximum wetting diameter increases with the decrease of static contact angle below the wetting limit temperatures..
116. Hiroyuki Hayashi, Koji Takahashi, Tatsuya Ikuta, Takashi Nishiyama, Yasuyuki Takata, Xing Zhang, Direct evaluation of ballistic phonon transport in a multi-walled carbon nanotube, Applied Physics Letters, 10.1063/1.4869470, 104, 11, 2014.03, Phonon confinement and in situ thermal conductance measurements in an individual multi-walled carbon nanotube (MWNT) are reported. Focused ion beam (FIB) irradiation was used to successively shorten a 4.8 μm long MWNT, eventually yielding a 0.3 μm long MWNT. After the first FIB irradiation, a 41% reduction in conductance was achieved, compared with that of the pristine MWNT. This was because the contributions from phonons with long free paths were excluded by scattering at FIB-induced defects. Phonon transport in linked multiple-length nanotubes was also investigated..
117. S. Fukuda, Masamichi Kohno, K. Tagashira, N. Ishihara, S. Hidaka, Yasuyuki Takata, Behavior of Small Droplet Impinging on a Hot Surface, HEAT TRANSFER ENGINEERING, 10.1080/01457632.2013.812496, 35, 2, 204-211, 2014.01.
118. S. Hussain, Y. Fukatani, Masamichi Kohno, K. Sefiane, Yasuyuki Takata, 2D simulation of FC72 sessile droplet evaporation in the constant contact line region, International Review of Mechanical Engineering, 8, 1, 52-61, 2014.01, A 2-dimensional simulation of FC72 sessile droplet evaporation on a substrate layer consisting of silicon and Kapton tape has been carried out to study the heat and fluid flow inside the droplet as well as its surroundings. The momentum and volume fraction (VOF) equations were solved simultaneously with the heat and diffusion equations to obtain the flow profiles. The simulated conditions were based on actual experiments. This paper presents the findings for the simulated experimental condition for the same substrate and surrounding temperature under a constant contact line condition. The initial conditions for the substrate, surroundings and droplet was set to, as best as possible, the same condition as the experiment. Quantitative as well as qualitative comparisons were made between the experimental and simulated results. The simulation also predicted the temperature and concentration fields inside and outside the evaporating droplet. The predicted temperature and heat transfer profiles were compared to experimental results and were found to be qualitatively agreeable..
119. Shinya Fukuda, Masamichi Kohno, Keisuke Tagashira, Nobuya Ishihara, Sumitomo Hidaka, Yasuyuki Takata, Behavior of small droplet impinging on a hot surface, Heat Transfer Engineering, 10.1080/01457632.2013.812496, 35, 2, 204-211, 2014.01, The effects of droplet diameter, surface roughness, and impinging velocity on the behavior of a droplet impinging on a hot surface were studied. The surface samples used in the experiment were cylinder blocks of stainless steel having four different degrees of roughness: Ra 0.04, Ra 0.2, Ra 3, and Ra 10. The diameter and impinging velocity were controlled independently using a microjet dispenser, and their values were in the ranges of 300-700 μm and 1.0-4.0 m/s, respectively. The contact time was found to increase with an increase in the surface roughness and was of the order of the self-oscillation of the water droplet. The maximum spread of the droplet decreased with increasing impinging velocity. A cooling curve was obtained for surface temperatures ranging from 500°C to 100°C, and the cooling time was found to decrease with an increase in the surface roughness of stainless steel. Moreover, the cooling effectiveness of each droplet increased with an increase in the surface roughness, a decrease in the droplet diameter, and an increase in the impinging velocity..
120. Hiroyuki Fukuda, Naoki Nakata, Hideo Kijima, Takashi Kuroki, Akio Fujibayashi, Yasuyuki Takata, Sumitomo Hidaka, Effects on surface conditions on spray cooling characteristics, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.100.1514, 100, 12, 1514-1522, 2014.01, The influence of surface conditions such as scale thickness and surface roughness on water spray cooling and air jet cooling characteristics was investigated experimentally. SUS304 stainless steel with the thickness of 20 mm was used as the cooled sample. An artificial scale layer was formed on the sample surface by thermal-spraying using Al2O3 powder. The thickness of the Al2O3 layer was varied from 50 μm to 210 μm. A sample without an artificial scale layer was also studied; in this case, the surface was roughened by shot blasting up to 20 μmRa. As a result, the artificial scale layer showed a thermal resistance function in both water spray cooling and air jet cooling. In water spray cooling, the characteristics of which depend on surface temperature, the cooling rate during film boiling and the apparent quench point temperature at the interface increased with Al2O3 scale thickness. Surface roughness enhanced the cooling rate during film boiling and resulted in a higher quench point temperature in spray cooling. In air jet cooling, heat flux increases with surface roughness, but this tendency can be seen only with larger flow rates. Surface roughness has a much stronger influence on heat flux in water spray cooling, even though the average heat flux is not as large. In this research, the heat flux during impingement of water droplets was estimated to be much higher than that in air jet cooling. This is thought to explain the difference in the influence of surface roughness on cooling characteristics with the two cooling methods..
121. Sivasankaran Harish, Mitsuru Tabara, Yoshifumi Ikoma, Zenji Horita, Yasuyuki Takata, David G. Cahill, Masamichi Kohno, Thermal conductivity reduction of crystalline silicon by high-pressure torsion, Nanoscale Research Letters, 10.1186/1556-276X-9-326, 9, 1, 2014.01, We report a dramatic and irreversible reduction in the lattice thermal conductivity of bulk crystalline silicon when subjected to intense plastic strain under a pressure of 24 GPa using high-pressure torsion (HPT). Thermal conductivity of the HPT-processed samples were measured using picosecond time domain thermoreflectance. Thermal conductivity measurements show that the HPT-processed samples have a lattice thermal conductivity reduction by a factor of approximately 20 (from intrinsic single crystalline value of 142 Wm-1 K-1 to approximately 7.6 Wm-1 K-1). Thermal conductivity reduction in HPT-processed silicon is attributed to the formation of nanograin boundaries and metastable Si-III/XII phases which act as phonon scattering sites, and because of a large density of lattice defects introduced by HPT processing. Annealing the samples at 873 K increases the thermal conductivity due to the reduction in the density of secondary phases and lattice defects..
122. Hiroyuki Moroizumi, Shohei Chiashi, Yasuyuki Takata, Masamichi Kohno, Water molecule adsorption on vertically aligned single-walled carbon nanotubes, ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2014, Collocated with the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2014, Collocated with the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, 10.1115/ICNMM2014-21468, 2014.01, A single walled carbon nanotube, which adsorbed water molecule in its nano channel, was observed using Raman spectroscopy, and two samples' spectrums were compared under the same conditions. The SWNT samples that were vertically aligned on the silicon substrate were used. One of the samples was not covered by polymer whereas the other sample was covered by polymer. In our experiment, a nano channel was made using a nanosecond pulse laser (Nd:YAG laser). In order to adjust the focus, the sample was set on the automatic stage and controlled on the PC using a USB camera to watch closely. By moving the stage for over 30 seconds, the sample was processed to make the nano channel. The cell with the laser-processed sample in it was set on the Raman spectroscopy's platform. Then, the cell was connected to the vacuum chamber and erlenmeyer flask by the valve. Both of the valves were opened first and left for a while to make the cell vacuum. Second, the vacuum chamber's valve was closed and left for a while to let water molecule spread in the cell. Finally, the SWNT successfully adsorbed water molecule in its nano channel. Ar-ion laser was used in the Raman spectroscopy and the laser wavelength is 488nm. With the Raman spectroscopy, Radial Breathing Mode (RBM), D-band, and G-band were mainly observed. The RBM, D-band, and G-band originated from radial vibration frequency, defective structure, and graphite structure respectively. According to the sample types, the RBM spectrums were compared in our experiment..
123. Ryosuke Nagahisa, Daiki Kuriya, Hidetaka Muramatsu, Yasuyuki Takata, Kuniyasu Ogawa, Kohei Ito, Measurement system for solubility and self-diffusivity of hydrogen gas dissolved in polymer electrolyte membrane, Journal of the Electrochemical Society, 10.1149/2.0881410jes, 161, 10, F1070-F1074, 2014, The characteristics of hydrogen gas permeation through a polymer electrolyte membrane (PEM) are important in determining the performance of electrochemical systems such as fuel cells and electrolyzers. However, the only available data related to these characteristics are those for the hydrogen permeability, which were obtained from measurements under a given pressure difference through the PEM. Although we can derive the solubility and self-diffusivity from the permeability, the derivation requires a mathematical procedure, such as providing a gas transport model and fitting experimental data with theoretical data from the model. In this study, we developed a measurement system that uses nuclear magnetic resonance and can quantify both the solubility and self-diffusivity in a rather straightforward manner. The system allows us to measure these two properties when hydrogen gas is dissolved in a dry Nafion membrane under a hydrogen gas pressure of up to 1 MPa at room temperature. The solubility increases linearly with increasing pressure, and the solubility coefficient is (1.3 ± 0.13) × 10-5 mol/(cm2MPa). The self-diffusivity shows a constant value of (2 ± 0.4) × 10-6 cm2/s regardless of the pressure..
124. Bambang Joko Suroto, Masahiro Tashiro, Sana Hirabayashi, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, A photographic study on the effects of hydrophobic-spot size and subcooling on local film boiling, ASME 2013 11th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM 2013 ASME 2013 11th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM 2013, 10.1115/ICNMM2013-73069, 2013.12, The effects of hydrophobic circle spot size and subcooling on local film boiling phenomenon from the copper surface with single PTFE (Polytetrafluoroethylene) hydrophobic circle spot at low heat flux has been investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0 and 10K. The heat transfer surfaces are used polished copper block with single PTFE hydrophobic circle spot of diameters 2, 4 and 6 mm, respectively. A high-speed camera was used to capture bubble dynamics and disclosed the sequence of the process leading to local film boiling. The result shows that local films boiling occurs on the PTFE circle spot at low heat flux and was triggered by the merging of neighboring bubbles. The study also showed that transition time required for change from nucleate boiling regime to local film boiling regime depends on the diameter of the hydrophobic circle spot and the subcooling. A stable local film boiling occurs at the smallest diameter of hydrophobic spot. Subcooling cause the local film boiling occur at negative superheat and oscillation of bubble dome..
125. Temujin Uehara, Kosuke Yoshimura, Elin Yusibani, Kan'ei Shinzato, Masamichi Kohno, Yasuyuki Takata, Hydrogen viscosity measurements with capillary tube under high pressure, ASME 2013 11th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM 2013 ASME 2013 11th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM 2013, 10.1115/ICNMM2013-73139, 2013.12, Viscosity of hydrogen has been measured at high pressures and high temperatures by using capillary tube method. The measurement apparatus was designed specifically for high pressure gas up to 100MPa. The capillary used quartz glass tube 0.1mm in inner diameter and 400mm in length. The measurement range is 0.1MPa to 100MPa, and room temperature up to 723K. We have to generate laminar flow inside the capillary tube that is the range of Reynolds number from 250 to 900. Since we measured nitrogen gas viscosity at the same range and many nitrogen viscosity data have already been measured in these ranges, nitrogen data was used in this study to confirm the accuracy of our apparatus before measurements of hydrogen. The measurement results of hydrogen are evaluated compared with our existing correlation(Yusibani Correlation)[1]. The results of hydrogen viscosity agree well with the existing correlation within 2% except for the measurements at 723K. The relative uncertainty of the present measurement system is estimated to be as much as 2%..
126. Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, Thermodynamic behavior of hydrogen binary systems with critical curve divergence and retrograde condensation, Journal of Thermal Science and Technology, 10.1299/jtst.8.603, 8, 3, 603-612, 2013.12, In binary systems of hydrogen and hydrocarbons, the fluid-phase thermodynamic behavior is unique in having the divergence of the critical curves to a high pressure region. The thermodynamic properties of the binary systems including hydrogen with methane, ethane, propane, and carbon dioxide were calculated from a Peng-Robinson equation of state (PR EOS). The mixing parameter of the present EOS has a functional form of temperature generalized by the critical temperatures of the hydrocarbons and carbon dioxide. Based on the corresponding states principle, the coefficients of the parameter were determined with a non-linear least squares fitting to the experimental critical points of the mixtures. The developed PR EOS shows good agreement with the experimental data of not only the critical points but also the phase equilibria. In the hydrogen binary systems, retrograde condensation is expected. The volumetric and enthalpy changes in this process were simulated for a hydrogen + carbon dioxide mixture of 0.55 mole fraction using the PR EOS at 270 K..
127. Yuki Fukatani, Takaaki Wakui, Suhaila Hussain, Masamichi Kohno, Yasuyuki Takata, Khellil Sefiane, Jungho Kim, Analysis of Droplet Evaporation Using IR Thermography, International Symposium on Innovative Materials for Process in Energy Systems 2013, 2013.09.
128. Khellil Sefiane, Yuki Fukatani, Yasuyuki Takata, Jungho Kim, Thermal Patterns and Hydrothermal Waves (HTWs) in Volatile Drops, LANGMUIR, 10.1021/la402247n, 29, 31, 9750-9760, 2013.08.
129. E.-S.R. Negeed, S. Hidaka, Masamichi Kohno, Yasuyuki Takata, Effect of the surface roughness and oxidation layer on the dynamic behavior of micrometric single water droplets impacting onto heated surfaces, INTERNATIONAL JOURNAL OF THERMAL SCIENCES, 10.1016/j.ijthermalsci.2013.03.004, 70, 65-82, 2013.08.
130. El Sayed R. Negeed, S. Hidaka, Masamichi Kohno, Yasuyuki Takata, Effect of the surface roughness and oxidation layer on the dynamic behavior of micrometric single water droplets impacting onto heated surfaces, International Journal of Thermal Sciences, 10.1016/j.ijthermalsci.2013.03.004, 70, 65-82, 2013.08, The present research study investigates the effects of surface roughness amplitude and surface oxide layer thickness on the dynamic behavior of micrometric single water droplets during collision with surfaces at high temperature. Stainless steel-grade 304 (SUS 304) surfaces of different amplitudes of surface roughness; Ra = 0.04, 2, 4, 6, 8 and 10 μm, have been considered. Each heat transfer surface was heated up to different temperatures; 1108, 1158 and 1198 K, to control the oxide layer thickness over the hot surface. An individual water droplet is ejected from a needle of the micro jet dispenser where the droplet's size and its velocity were controlled independently. The behavior of droplet during the collision with hot surface was observed with a high-speed camera. By analyzing the experimental results, the effects of the surface roughness amplitude, oxide layer thickness, droplet Weber number, and surface superheat on the hot solid-liquid contact time, and on the maximum droplet spread diameter were investigated. Empirical correlations have been deduced describing the relationship between the hydrodynamic characteristics of an individual droplet impinging on a heated surface and concealing the affecting parameters in such process. Also, the comparison between the current results and the results due to other investigators shows the effects of oxide layer thickness and surface roughness amplitude on the impact behavior of water droplet onto the heated surfaces..
131. Bambang Joko Suroto, Masahiro Tashiro, Sana Hirabayashi, Sumitomo Hidaka, Masamichi Kohno, Yasuyuki Takata, Effects of hydrophobic-spot periphery and subcooling on nucleate pool boiling from a mixed-wettability surface, Journal of Thermal Science and Technology, 10.1299/jtst.8.294, 8, 1, 294-308, 2013.08, The effect of subcooling and length of hydrophobic-spot periphery on nucleate pool boiling heat transfer from TiO2-coated surface with and without PTFE (polyetatafluoroethylene) hydrophobic circle spots at intermediate heat flux has been examined. The experiments are performed with liquid subcooling ranging from 0-20 K and heat transfer block used were TiO2-coated copper block with a PTFE hydrophobic circle spot with various diameters with total area of PTFE being constant. Bubble nucleation and behavior were observed by using high-speed camera. The results showed that the heat transfer performance of surfaces with PTFE hydrophobic circle spot is better than superhydrophilic surface in overall condition. Furthermore, the heat transfer performance decreases under subcooled condition for all surfaces. Increase in peripheral length of hydrophobic-spot enhances the heat transfer performance..
132. Khellil Sefiane, Yuki Fukatani, Yasuyuki Takata, Jungho Kim, Thermal patterns and hydrothermal waves (HTWs) in volatile drops, Langmuir, 10.1021/la402247n, 29, 31, 9750-9760, 2013.08, Experimental measurements of temperature and heat flux at the liquid-wall interface during the evaporation of sessile FC-72 droplets have been reported for the first time using infrared (IR) thermography. Simultaneous high-speed imaging of the evaporating drop was carried out to monitor the drop profile. The study demonstrates that recently evidenced hydrothermal waves are actually bulk waves that extend across the entire droplet volume. More importantly, thermal patterns occurring in the bulk of the drop affect the temperature and heat-flux distributions on the solid substrate and ultimately influence the droplet evaporation rate. These effects were found to be increasingly pronounced as the substrate temperature was raised. The implications for heat-transfer mechanisms and energy transport are discussed..
133. Bambang Joko Suroto, Masahiro Tashiro, Sana Hirabayashi, Sumitomo Hidaka, Masamichi Kohno, Yasuyuki Takata, Effects of Hydrophobic-Spot Periphery and Subcooling on Nucleate Pool Boiling from a Mixed-Wettability Surface, Journal of Thermal Science and Technology, 8, 1, 294-308, 2013.07.
134. T. Uehara, K. Yoshimura, E. Yusibani, K. Shinzato, Masamichi Kohno, Yasuyuki Takata, Hydrogen Viscosity Mesurements with Capillary Tube under High Pressure, The ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2013-73139, 2013.06.
135. B. J. Suroto, M Tashiro, S. Hirabayashi, S. Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, A Photographic Study on the Effects of Hydrophobic-Spot Size and Subcooling on Local Film Boiling, The ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2013-73069, 2013.06.
136. Elin Yusibani, Peter L. Woodfield, K. Shinzato, Yasuyuki Takata, Masamichi Kohno, A compact curved vibrating wire technique for measurement of hydrogen gas viscosity, Experimental Thermal and Fluid Science, Vol. 47, 1-5, 2013.05.
137. Yasuyuki Takata, B. J. Suroto, M. Tashiro, S. Hidaka, Masamichi Kohno, Wettability Effects in Boiling Heat Transfer, Proceedings of the 8th International Conference on Multiphase Flow (ICMF2013), 2013.05.
138. E. Yusibani, P. L. Woodfield, K. Shinzato, Yasuyuki Takata, Masamichi Kohno, A compact curved vibrating wire technique for measurement of hydrogen gas viscosity, Experimental Thermal and Fluid Science, 10.1016/j.expthermflusci.2012.11.008, 47, 1-5, 2013.05, Studies with the view to application of a curved vibrating wire method to measure hydrogen gas viscosity have been done. A fine tungsten wire with a nominal diameter of 50. μm is bent into a semi-circular shape and arranged symmetrically in a magnetic field. The frequency domain response for forced oscillation of the wire is used for calculating the viscosity. Argon, nitrogen, helium and hydrogen viscosities have been measured at room temperature up to 0.7. MPa. The deviations with respect to existing equations suggest that with more refinements it may be possible to take gas viscosity measurements with a precision of less than 1%..
139. Yasuyuki Takata, Special issue on power and energy systems, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 79, 799, 2013.05.
140. El-Sayed R. Negeed, Sumitomo Hidaka, Masamichi Kohno, Yasuyuki Takata, High speed camera investigation of the impingement of single water droplets on oxidized high temperature surfaces, INTERNATIONAL JOURNAL OF THERMAL SCIENCES, 10.1016/j.ijthermalsci.2012.07.014, 63, 1-14, 2013.01.
141. El Sayed R. Negeed, S. Hidaka, Masamichi Kohno, Yasuyuki Takata, High speed camera investigation of the impingement of single water droplets on oxidized high temperature surfaces, International Journal of Thermal Sciences, 10.1016/j.ijthermalsci.2012.07.014, 63, 1-14, 2013.01, This study investigates the influence of oxide layer over the hot surfaces on the behavior of single droplets impacting the high temperature surfaces using high speed camera. In the present work, an experimental apparatus was installed where direct contact between mono-dispersed water droplet and solid hot surface in the presence of different values of oxide layer (4.5, 6.7, 9.4 and 12.6 μm) over the hot surface was experimentally investigated. The droplets size and its velocity were controlled independently. The results presented the effects of surface oxide layer, droplet velocity, droplet size and surface superheating on the hot solid-liquid contact wettability time and on the maximum droplet spread diameter on the hot surface. Empirical correlations are presented describing the hydrodynamic characteristics of an individual droplet impinging on a heated surface and concealing the affecting parameters for surface oxidation phenomena in such process. Also, the comparison between the obtained results at oxidation phenomena and the results due to others at non oxidation phenomena shows the effect of surface oxidation phenomena on the behavior of single droplet impacting the high temperature surface. These experimental observations provide the validation data required for multi-phase modeling of these phenomena by computational fluid dynamics (CFD) (e.g. Volume of Fluid (VOF) modeling) methods..
142. Yutaka Yamada, Tatsuya Ikuta, Takashi Nishiyama, Koji Takahashi, Yasuyuki Takata, Submicron-scale condensation on hydrophobic and hydrophilic surfaces, ASME 2013 International Mechanical Engineering Congress and Exposition, IMECE 2013 Safety, Reliability and Risk; Virtual Podium (Posters), 10.1115/IMECE2013-66186, 2013.01, Condensation heat transfer is a widely-used technique for industrial applications represented by heat exchanger because of its high heat transfer coefficient. To enhance its performance, a suitable surface is required, where both condensation and droplet removal smoothly occur. In this study, we compared wettability of a graphene surface and an amorphous carbon surface. The result shows that an amorphous carbon surface is more hydrophilic. Then we prepared a graphite surface which has nanoscale hydrophilic regions in large hydrophobic area. We observed the submicron-scale droplet condensation occurs preferentially on the hydrophilic graphite step by using environmental scanning electron microscope (ESEM)..
143. Shinri Nonaka, Tastuhiro Mori, Yasuyuki Takata, Masamichi Kohno, The effect of the laser beam wavelength and pulse width on micro grooving
Comparison of nanosecond and femtosecond laser, ASME 2012 10th Int. Conf. on Nanochannels, Microchannels, and Minichannels, ICNMM 2012 Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 Fluids Engineering Division Sum, ICNMM 2012 ASME 2012 10th Int. Conf. on Nanochannels, Microchannels, and Minichannels Collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Sum, ICNMM 2012, 10.1115/ICNMM2012-73135, 275-280, 2012.12, Processing technique of micro grooves and channels is very important to study the phenomenon of fluids in micro scale. Micro grooves and microchannels play an important role in various devices, such as μ-TAS (Micro-Total Analysis Systems) and micro reactors. Laser processing is currently widely used for drilling and grooving of various materials including metals, polymers, glasses and composite materials, since laser machining can avoid the problems that conventional machining methods have. For example wear of a working tool, lowering of processing accuracy, and wear debris becoming contaminants are some of the problems of the conventional method. Additionally, compared to other non-contact machining processes such as electron beam machining (EBM) and focused ion beam (FIB), machining a vacuum is not required. Therefore, applicability is wider and setup costs can be more economical..
144. Kazuhide Shibata, Yohei Tasaki, Yasuyuki Takata, Makoto Hirasawa, Takefumi Seto, Masamichi Kohno, Size classification of CNTs in gas flow with differential mobility analyzer (DMA), Proceedings of the 3rd International Forum on Heat Transfer, IFHT2012-186, 2012.11.
145. Takashi Nishiyama, Takanori Nakayama, Koji Takahashi, Yasuyuki Takata, The effect of nanocarbon materials on surface wettability, Proceedings of the 3rd International Forum on Heat Transfer, IFHT2012-173, 2012.11.
146. Temujin Uehara, Kousuke Yoshimura, Elin Yusibani, Kan'ei Shinzato, Masamichi Kohno, Yasuyuki Takata, Measurements of hydrogen viscosity with capillary tube method up to 773K and 100MPa, Proceedings of the 3rd International Forum on Heat Transfer, IFHT2012-187, 2012.11.
147. Keisuke Kubo, Naoya Sakoda, Koich Motomura, Supriatno, Kan'ei Shinzato, Masamichi Kohno, Yasuyuki Takata, PVT property measurements of hydrogen in the range from 473 K to 773 K and up to 100 MPa by the isochoric method, Proceedings of the 3rd International Forum on Heat Transfer, IFHT2012-188, 2012.11.
148. Shinri Nonaka, Tatsuhiro Mori, Yasuyuki Takata, Masamichi Kohno, The Effect of the Laser Beam Wavelength and Pulse Width on Micro Grooving: Comparison of Nanosecond and Femtosecond Laser, Proceedings of the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2012-73135, 2012.07.
149. M. Tashiro, B.J. Suroto, T. Kakitani, S. Hidaka, Masamichi Kohno, Yasuyuki Takata, Subcooled Boiling from a Surface with Spotted Patterns of Hydrophilic and Hydrophobic Coatings, Proceedings of the ECI-8th International Conference on Boiling and Condensation, 1520, 2012.06.
150. Y. Fukatani, S. Fukuda, S. Hidaka, Masamichi Kohno, Yasuyuki Takata, Heat Transfer of Small Droplet Impinging onto a Hot Surface (Effects of Droplet Diameter,Impinging Velocity, Surface Roughness), Proceedings of the ECI-8th International Conference on Boiling and Condensation, 1521, 2012.06.
151. Yasuyuki Takata, Sumitomo Hidaka, Masamichi Kohno, Effect of Surface Wettability on Pool Boiling -Enhancement by Hydrophobic Coating-, International Journal of Air-Conditioning and Refrigeration, 20, 1, 1150003, 2012.03.
152. Masamichi Kohno, Yohei Tasaki, Kazuhide Shibata, Yasuyuki Takata, Makoto Hirasawa, Takafui Seto, CNTs Synthesis in Gas Flow with Size Selected Metal Nano Particles Prepared by Laser Ablation Technique, Proceedings of the 8th KSME-JSME Thermal and Fluids Engineering Conference, FR11-009, 2012.03.
153. Bambang Joko Suroto, Masahiro Tashiro, Tsugutaka Kakitani, Sumitomo Hidaka, Masamichi Kohno, Yasuyuki Takata, Enhancement of Heat Transfer in Pool Boiling by Using a Patterned Hydrophobic Coating on Polished Copper Surface, Proceedings of the 8th KSME-JSME Thermal and Fluids Engineering Conference, GST03-003, 2012.03.
154. Yasuyuki Takata, Sumitomo Hidaka, Masamichi Kohno, Effect of Surface Wettability on Pool Boiling -Enhancement by Hydrophobic Coating-, International Journal of Air-Conditioning and Refrigeration , Vo.20, 1, 1150003, 2012.03.
155. Naoya Sakoda, K. Shindo, K. Motomura, K. Shinzato, Masamichi Kohno, Yasuyuki Takata, M. Fujii, Burnett PVT Measurements of Hydrogen and the Development of a Virial Equation of State at Pressures up to 100 MPa, International Journal of Thermophysics, Vol. 33, No. 3, 381-395, 2012.03.
156. N. Sakoda, K. Shindo, K. Motomura, K. Shinzato, M. Kohno, Y. Takata, M. Fujii, Burnett PVT measurements of hydrogen and the development of a virial equation of state at pressures up to 100 MPa, International Journal of Thermophysics, 10.1007/s10765-012-1168-2, 33, 3, 381-395, 2012.03, PVT properties weremeasured for hydrogen by the Burnettmethod in the temperature range from 353K to 473K and at pressures up to 100MPa. In the present Burnett method, the pressure measurement was simplified by using an absolute pressure transducer instead of a differential pressure transducer, which is traditionally used. The experimental procedures become easier, but the absolute pressure transducer is set outside the constant temperature bath because of the difficulty of its use in the bath, and the data acquisition procedure is revised by taking into account the effects of the dead space in the absolute pressure transducer. The measurement uncertainties in temperature, pressure, and density are 20mK, 28kPa, and 0.07% to 0.24% (k = 2), respectively. Based on the present data and other experimental data at low temperatures, a virial equation of state (EOS) from 220K to 473K and up to 100MPa was developed for hydrogen with uncertainties in density of 0.15%(k = 2) at P ≤ 15MPa, 0.20 % at 15 MPa < P ≤ 40 MPa, and 0.24 % at P > 40 MPa, and this EOS shows physically reasonable behavior of the second and third virial coefficients. Isochoric heat capacities were also calculated from the virial EOS and were compared with the latest EOS of hydrogen. The calculated isochoric heat capacities agree well with the latest EOS within 0.5% above 300K and up to 100MPa, while at lower temperatures, as the pressure increases, the deviations become larger (up to 1.5 %)..
157. N. Sakoda, K. Shindo, K. Motomura, K. Shinzato, M. Kohno, Y. Takata, M. Fujii, Burnett Method with Absolute Pressure Transducer and Measurements for PVT Properties of Nitrogen and Hydrogen up to 473 K and 100MPa, International Journal of Thermophysics, 33, 1, 6-21, 2012.01.
158. Naoya Sakoda, K. Shindo, K. Motomura, K. Shinzato, Masamichi Kohno, Yasuyuki Takata, M. Fujii, Burnett method with absolute pressure transducer and measurements for PVT properties of nitrogen and hydrogen up to 473 K and 100MPa, International Journal of Thermophysics, 10.1007/s10765-011-1120-x, 33, 1, 6-21, 2012.01, Ameasurement method for PVT properties of high-temperature and highpressure gases was developed by simplifying the Burnett method and revising the data acquisition procedure. Instead of a differential pressure transducer, which is traditionally used, an absolute pressure transducer is used in the present method, and the measurement of pressure becomes easier. However, the absolute pressure transducer is placed outside the constant temperature bath because of the difficulty of its use in high-temperature surroundings, and some parts with different temperatures from the sample vessels exist as dead space. The present method takes into account the effect of the dead space in the data acquisition procedure. Nitrogen was measured in the temperature range from 353K to 473K and at pressures up to 100MPa to determine the apparatus constants, and then, hydrogenwasmeasured at 473Kand up to 100MPa. The determined densities are in agreement within uncertainties of 0.07% to 0.24% (k = 2), both with the latest equation of state and existing measured data..
159. Adhika Widyaparaga, Masashi Kuwamoto, Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, Theoretical and experimental study of a flexible wiretype Joule-Thomson microrefrigerator for use in cryosurgery, Journal of Heat Transfer, 10.1115/1.4004937, 134, 2, 2012.01, We have developed a model capable of predicting the performance characteristics of a wiretype Joule-Thomson microcooler intended for use within a cryosurgical probe. Our objective was to be able to predict cold tip temperature, temperature distribution, and cooling power using only inlet gas properties as input variables. To achieve this, the model incorporated gas equations of state to account for changing gas properties due to heat transfer within the heat exchanger and expansion within the capillary. In consideration of inefficiencies, heat in-leak from free convection and radiation was also considered and the use of a 2D axisymmetric finite difference code allowed simulation of axial conduction. To validate simulation results, we have constructed and conducted experiments with two types of microcoolers differing in inner tube material, poly-ether-ether-ketone (PEEK) and stainless steel. The parameters of the experiment were used in the calculations. CO 2 was used as the coolant gas for inlet pressures from 0.5 MPa to 2.0 MPa. Heat load trials of up to 550 mW along with unloaded trials were conducted. The temperature measurements show that the model was successfully able to predict the cold tip temperature to a good degree of accuracy and well represent the temperature distribution. For the all PEEK microcooler in a vacuum using 2.0 MPa inlet pressure, the calculations predicted a temperature drop of 57 K and mass flow rate of 19.5 mg/s compared to measured values of 63 K and 19.4 mg/s, therefore, showing that conventional macroscale correlations can hold well for turbulent microscale flow and heat transfer as long as the validity of the assumptions is verified..
160. Adhika Widyaparaga, Masashi Kuwamoto, Eiji Noda, Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, Analytical optimization of heat exchanger dimensions of a joule-thomson microcooler, ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2011 ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2011, 10.1115/ICNMM2011-58205, 203-207, 2011.12, In designing a Joule-Thomson microcooler, aiming for a compact size yet maintaining good performance, it is important to find the optimum dimensions of its heat exchanger. We have developed a model capable of predicting the performance characteristics of a wiretype Joule-Thomson microcooler utilizing analytical methods and incorporating changing gas properties via gas equations of state. The model combined the heat exchanger and the JT expander, thus requiring only the inlet gas properties as input. The model results were compared to experimental measurements using C2H4 and N2O as coolant gases. Predicted mass flow rate and temperature drop were in good agreement with the measured values. The long capillary length present in the tested microcooler was revealed to maintain performance of the microcooler for longer heat exchanger lengths due to it functioning as a secondary heat exchanger. Using the calculation results it was possible to correctly estimate the optimum heat exchanger length for C2H 4 and for N2O..
161. Masahiro Tomoda, Teppei Kawahara, Yohei Tasaki, Yasuyuki Takata, Makoto Hirasawa, Takafumi Seto, Masamichi Kohno, Carbon nanotube synthesis from metal nanoparticles sizeclassified by a differential mobility analyzer, ASME/JSME 2011 8th Thermal Engineering Joint Conference, AJTEC 2011 ASME/JSME 2011 8th Thermal Engineering Joint Conference, AJTEC 2011, 2011.12, In this study, carbon nanotubes (CNTs) were synthesized from size-classified catalyst metal nanoparticles to observe the effect of the nanoparticles' diameter on the diameter of the CNTs. The nanoparticles were generated by laser vaporization and classified by a differential mobility analyzer, which sorts them by diameter according to differences in electrical mobility. After classification, the nanoparticles were collected on a Si substrate. CNTs were synthesized from these catalyst metal nanoparticles by using chemical vapor deposition. This experiment synthesized mainly multi-walled carbon nanotubes (MWNTs), with a small amount of single-walled carbon nanotubes (SWNTs). The reason is thought to be that the particles' diameters were appropriate for MWNT synthesis..
162. Ryosuke Nagahisa, Daiki Kuriya, Kuniyasu Ogawa, Yasuyuki Takata, Kohei Ito, Measurement of hydrogen-gas solubility and diffusivity in polymer electrolyte membrane by NMR method, 11th Polymer Electrolyte Fuel Cell Symposium, PEFC 11 - 220th ECS Meeting Polymer Electrolyte Fuel Cells 11, 10.1149/1.3635673, 41, 1423-1430, 2011.12, Polymer electrolyte membrane (PEM) used for fuel cells and water electrolyzers is permeable to hydrogen gas, and the permeation causes to decrease the performance as electrochemical system. So, it is necessary to figure out the mechanism of hydrogen gas permeation and to develop the PEM that has lower gas permeability. In this study, we developed a new measurement system for hydrogen-gas solubility and diffusivity in PEM based on NMR method, which enables us to derive the solubility and diffusivity without assuming theoretical dissolution model. We apply the system to the dissolved hydrogen-gas in dry Nafion®117. The solubility obtained is proportional to ambient pressure and 2.9×10 -5 mol/cm 3@0.7MPa. The diffusivity is 3×10 -10 m 2/s. These values are discussed with comparing the values measured in conventional method..
163. Koichi Kimura, Shogo Moroe, Peter Woodfield, Jun Fukai, Kan'ei Shinzato, Masamichi Kohno, Motoo Fujii, Yasuyuki Takata, Thermal conductivity measurement of hydrogen at high pressure and high temperature, ASME/JSME 2011 8th Thermal Engineering Joint Conference, AJTEC 2011 ASME/JSME 2011 8th Thermal Engineering Joint Conference, AJTEC 2011, 2011.12, The thermal conductivities and thermal diffusivities of hydrogen were measured with a transient short hot wire method for temperature range up to 300 °C and pressure range up to100MPa. The measured thermal conductivities showed good reproducibility and agreed with the existing values within a deviation of ±2%..
164. Adhika Widyaparaga, Takao Koshimizu, Eiji Noda, Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, The frequency dependent regenerator cold section and hot section positional reversal in a coaxial type thermoacoustic Stirling heat pump, Cryogenics, 10.1016/j.cryogenics.2011.09.001, 51, 10, 591-597, 2011.10, We have constructed and tested two travelling wave thermoacoustic heat pumps using a coaxial configuration with the regenerator positioned in the annulus. We discovered a frequency dependent positional reversal of the cold section and hot section of the regenerator within the test frequency range. By decomposing the measured pressure wave within the annulus, we obtained the positive (w+) and negative (w-) propagating travelling waves. It has been revealed the change of frequency is accompanied by a change in magnitudes of w+ and w- which is in part influenced by the presence of travelling wave attenuation through the regenerator. The resulting change of dominant travelling wave on a given end of the regenerator will then change the direction of thermoacoustic heat pumping at that end. This will alter the regenerator temperature distribution and may reverse the cold and hot sections of the regenerator. As the reversal does not require additional moving parts, merely a change in frequency, this feature in coaxial travelling wave devices has tremendous potential for applications which require both heating and cooling operation..
165. Yuki Fukatani, Shinya Fukuda, Sumitomo Hidaka, Makoto Arita, Masamichi Kohno, Yasuyuki Takata, Effect of roughness on the Behavior of Small Droplet Impinging onto a Hot Surface, Proceedings of the 4th International Conference on Heat Transfer and Fluid Flow in Microscale HTFFM-IV, 2011.09.
166. S. Moroe, P. L. Woodfield, K. Kimura, Masamichi Kohno, Jun Fukai, M. Fujii, K. Shinzato, Yasuyuki Takata, Measurements of hydrogen thermal conductivity at high pressure and high temperature, International Journal of Thermophysics, 10.1007/s10765-011-1052-5, 32, 9, 1887-1917, 2011.09, The thermal conductivity for normal hydrogen gas was measured in the range of temperatures from 323 K to 773 K at pressures up to 99 MPa using the transient short hot-wire method. The single-wire platinum probes had wire lengths of 10 mm to 15 mm with a nominal diameter of 10 μm. The volume-averaged transient temperature rise of the wire was calculated using a two-dimensional numerical solution to the unsteady heat conduction equation. A non-linear least-squares fitting procedure was employed to obtain the values of the thermal conductivity required for agreement between themeasured temperature rise and the calculation. The experimental uncertainty in the thermal-conductivity measurements was estimated to be 2.2 % (k = 2). An existing thermal-conductivity equation of state was modified to include the expanded range of conditions covered in the present study. The new correlation is applicable from 78 K to 773 K with pressures to 100 MPa and is in agreement with the majority of the present thermal-conductivity measurements within ±2 %..
167. Masamichi Kohno, Shinya Fukuda, Keisuke Tagashira, Nobuya Ishihara, Sumitomo Hidaka, Makoto Arita, Yasuyuki Takata, Study on the Behavior of Small Droplet Impinging onto a Hot Surface, Proceeding of 3rd Micro and Nano Flows Conference, 2011.08.
168. Y. Takata, S. Hidaka, K. Tagashira, S. Fukuda, B. J. Suroto, M. Kohno, Effect of Surface Conditions on Boiling and Evaporation, Proceedings of International Conference on Air-Conditioning & Refrigeration 2011, ICACR2011-KN-3, 2011.07.
169. M. J. Assael, J.-A. M. Assael, M. L. Huber, R. A. Perkins, and Y. Takata, Correlation of the Thermal Conductivity of Normal and Parahydrogen from the Triple Point to 1000 K and up to 100 MPa, Journal of Physical and Chemical Reference Data, 10.1063/1.3606499, 40, 3, 033101, 2011.07.
170. S. Moroe, P. L. Woodfield, K. Kimura, M. Kohno, J. Fukai, M. Fujii, K. Shinzato, Y. Takata, Measurements of Hydrogen Thermal Conductivity at High Pressure and High Temperature, International Journal of Thermophysics, 32, 9, 1887-1917, 2011.07.
171. M. J. Assael, J. A.M. Assael, M. L. Huber, R. A. Perkins, Y. Takata, Correlation of the Thermal Conductivity of Normal and Parahydrogen from the Triple Point to 1000 K and up to 100 MP, Journal of Physical and Chemical Reference Data, 10.1063/1.3606499, 40, 3, 2011.07, This paper contains new, representative equations for the thermal conductivity of normal and parahydrogen. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. Although there are sufficient data at normal temperatures, data at very low or very high temperatures as well as near the critical region are scarce. In the case of the dilute-gas thermal conductivity, a new theoretically based correlation was adopted, as it agreed very well with the existing data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 1000 K and pressures up to 100 MPa for both normal hydrogen and parahydrogen..
172. Adhika Widyaparaga, Masashi Kuwamoto, Eiji Noda, Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, Analytical Optimization of Heat Exchanger Dimensions of a Joule-Thomson Microcooler, Proceedings of ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2011-58205, 2011.06.
173. Elin Yusibani, Yosuke Nagahama, Masamichi Kohno, Yasuyuki Takata, Peter L. Woodfield, Kanei Shinzato, Motoo Fujii, A capillary tube viscometer designed for measurements of hydrogen gas viscosity at high pressure and high temperature, International Journal of Thermophysics, 10.1007/s10765-011-0999-6, 32, 6, 1111-1124, 2011.06, A capillary tube viscometer was developed to measure the dynamic viscosity of gases for high pressure and high temperature. The apparatus is simple and designed for safe-handling operation. The gas was supplied to the capillary tube from a high-pressure reservoir tank through a pressure regulator unit to maintain a steady state flow. The measurements of a pressure drop across the capillary tube with high accuracy under extreme conditions are the main challenge for this method. A differential pressure sensor for high pressures up to 100MPa is not available commercially. Therefore, a pair of accurate absolute pressure transducers was used as a differential pressure sensor. Then the pressure drop was calculated by subtracting the outlet pressure from the inlet one with a resolution of 100 Pa at 100 MPa. The accuracy of the present measurement system is confirmed by measuring the viscosity of nitrogen as a reference gas. The apparatus provided viscosities of nitrogen from ambient temperature to 500K and hydrogen from ambient temperature to 400 K and for pressures up to 100MPa with a maximum deviation of 2.2% compared with a correlation developed by the present authors and with REFPROP (NIST)..
174. S. Moroe, P. L. Woodfield, J. Fukai, K. Shinzato, M. Kohno, M. Fujii, Y. Takata, Thermal conductivity measurement of gases by the transient short-hot-wire method, Experimental Heat Transfer, 10.1080/08916152.2010.503310, 24, 2, 168-178, 2011.04, Measurements of the thermal conductivity of helium and hydrogen are performed using the transient short-hot-wire method. The short hot wire is made of platinum and has a diameter of about 10 μm and a length of about 15 mm. It is attached by spot welding to platinum terminals with a diameter of 1.5 mm. The probe is inserted into the sample vessel that has a volume of 35 cm 3 and an inner diameter of 30 mm. The thermal conductivity is evaluated by comparing a numerical solution of the heat conduction in and around the short wire with the experimentally obtained temperature rise of the wire. The measured thermal conductivities show good reproducibility. Also, the measured thermal conductivities agree with the reference equations within a deviation of ± 1%..
175. Masahiro Tomoda, Teppei Kawahara, Yohei Tasaki, Yasuyuki Takata, Makoto Hirasawa, Takafumi Seto, Masamichi Kohno, Carbon Nanotube Synthesis from Metal nanoparticles Size-Classified by a Differential Mobility Analyzer, Proceedings of the ASME/JSME 2011 8th Thermal Engineering Joint Conference (AJTEC2011), AJTEC2011-44414, Honolulu, Hawaii, 2011.03.
176. Koich Kimura, Shogo Moroe, Peter Woodfield, Jun Fukai, Kan’ei Shinzato, Masamichi Kohno, Motoo Fujii, Yasuyuki Takata, Thermal Conductivity Measurement of Hydrogen at High Pressure and High Temperature, Proceedings of the ASME/JSME 2011 8th Thermal Engineering Joint Conference (AJTEC2011), AJTEC2011-44415, Honolulu, Hawaii, 2011.03.
177. El-Sayed R. Negeed, S. Hidaka, M. Kohno, Y. Takata, Experimental and analytical Investiogation of Liquid Sheet Breakup Characteristics, International Journal of Heat and Fluid Flow, 32, 1, 95-106, 2011.02.
178. El Sayed R. Negeed, S. Hidaka, Masamichi Kohno, Yasuyuki Takata, Experimental and analytical investigation of liquid sheet breakup characteristics, International Journal of Heat and Fluid Flow, 10.1016/j.ijheatfluidflow.2010.08.005, 32, 1, 95-106, 2011.02, The main objective of this research is to study analytically and experimentally the liquid sheet breakup of a flat fan jet nozzle resulting from pressure-swirling. In this study the effects of nozzle shape and spray pressure on the liquid sheet characteristics were investigated for four nozzles with different exit widths (1.0, 1.5, 2.0 and 2.5. mm). The length of liquid sheet breakup, liquid sheet velocity and the size of formed droplets were measured by a digital high speed camera. The breakup characteristics of plane liquid sheets in atmosphere are analytically investigated by means of linear and nonlinear hydrodynamic instability analyses. The liquid sheet breakup process was studied for initial sinuous and also varicose modes of disturbance. The results presented the effect of the nozzle width and the spray pressure on the breakup length and also on the size of the formed droplets. Comparing the experimental results with the theoretical ones for all the four types of nozzles, gives a good agreement with difference ranges from 4% to 12%. Also, the comparison between the obtained results and the results due to others shows a good agreement with difference ranged from 5% to 16%. Empirical correlations have been deduced describing the relation between the liquid sheet breakup characteristics and affecting parameters; liquid sheet Reynolds number, Weber number and the nozzle width..
179. Masamichi Kohno, Teppei Kawahara, Masahiro Tomoda, Yasuyuki Takata, Shuhei Inoue, Shinzo Suzuki, Shigeo Maruyama, Synthesis of single-walled carbon nanotubes using laser-vaporized metal nanoparticle catalyst, Journal of Mechanical Science and Technology, 10.1007/s12206-010-1110-0, 25, 1, 11-15, 2011.01, SWNTs were synthesized by laser-vaporized CCVD (catalytic chemical vapor deposition). The diameter distributions and the abundance of SWNTs synthesized at different temperatures and using different catalysts were investigated by Raman spectroscopy. Further, this technique was compared with other synthesis techniques (laser-oven and conventional-alcohol CCVD), and C60 was synthesized simultaneously as a byproduct only using the laser-oven technique. With increasing synthesis temperature, the diameter distribution shifted towards larger diameters, and the G/D ratio became larger as the synthesis temperature increased to 1000°C. Ni, Co, and Fe played a catalytic role, though Fe was less effective under our experimental conditions. The diameter distribution of SWNTs synthesized with the Fe catalyst was shifted to smaller values compared to those synthesized with Ni or Co catalysts..
180. El-Sayed R. Negeed, N. Ishihara, K. Tagashira, S. Hidaka, M. Kohno, Y. Takata, Experimental study on the effect of surface conditions on evaporation of sprayed liquid droplet, International Journal of Thermal Sciences, 49, 12, 2250-2271, 2010.12.
181. S. Momoki, O. Jambal, T. Yamaguchi, R. Akasaka, Y. Takata, An Application of Hydrogen Thermophysical Properties Database “All in One Live CD”, International Jouranl of Thermophysics, 31, 11-12, 2394-2401, 2010.12.
182. S. Momoki, O. Jambal, T. Yamaguchi, R. Akasaka, Y. Takata, An application of hydrogen thermophysical properties database "all in one live CD", International Journal of Thermophysics, 10.1007/s10765-010-0873-y, 31, 11-12, 2394-2401, 2010.12, A database for the thermophysical properties of hydrogen that supports a wide range of parameters including high pressures and high temperatures is being developed. The database performance requirements were studied and, in this paper, an application that combines a server-client database and a live CD is proposed. For this, an "All in One Live CD" application has been developed. Web interfaces provide excellent user interfaces for databases. However, there are some disadvantages for web interfaces related to server maintenance and access restrictions. This new application, the "All in One Live CD," is free of these disadvantages, and provides a database with a property estimation service independent of the computer environment. From a single boot via the "All in One Live CD," the database becomes accessible on multiple computers so that this feature makes the new application a unique solution as a distribution media..
183. El Sayed R. Negeed, N. Ishihara, K. Tagashira, S. Hidaka, M. Kohno, Y. Takata, Experimental study on the effect of surface conditions on evaporation of sprayed liquid droplet, International Journal of Thermal Sciences, 10.1016/j.ijthermalsci.2010.08.008, 49, 12, 2250-2271, 2010.12, The present study investigates experimentally the effects of thermal properties of the hot surface and droplet characteristics on the droplet evaporation. Cylindrical blocks made of Stainless Steel, Aluminum and Brass with different degrees of surface roughness were used. The droplet diameter and velocity were controlled independently. The behavior of droplet during the collision with hot surface was observed with a high-speed camera. The results presented the effect of the thermal properties of the hot surface, droplet Weber number, droplet velocity, droplet size, hot surface conditions; surface superheat and degree of surface roughness on the solid-liquid contact time and the maximum spread of droplet over the surface. Empirical correlations have been deduced describing the relationship between the hydrodynamic characteristics of an individual droplet impinging on a heated surface and concealing the affecting parameters in such process. Also, the comparison between the current results and the results due to others investigators shows good agreement in which the difference between them ranged from 5% to 25%..
184. Adhika Widyaparaga, Masashi Kuwamoto, Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, Theoretical study of a flexible wiretype Joule Thomson micro-refrigerator for use in cryosurgery, ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2010 Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 10.1115/FEDSM-ICNMM2010-30127, 591-598, 2010.12, We have developed a model capable of predicting the performance characteristics of a wiretype Joule-Thomson microcooler intended for use within a cryosurgical probe. Our objective was to be able to predict evaporator temperature, temperature distribution and cooling power using only inlet gas properties as input variables. To achieve this, the model incorporated changing gas properties due to heat transfer within the heat exchanger and isenthalpic expansion within the capillary. In consideration of inefficiencies, heat in-leak from free convection and radiation was also considered and the use of a 2D axisymmetric finite difference code allowed simulation of axial conduction. Two types of microcoolers differing in inner tube material, poly-ether-ether-ketone (PEEK) and stainless steel, were tested and simulated. CO2 was used as the coolant gas in the calculations and experimental trials for inlet pressures from 0.5 MPa to 2.0 MPa. Heat load trials of up to 550 mW along with unloaded trials were conducted. Comparisons to experiments show that the model was successfully able to obtain a good degree of accuracy. For the all PEEK microcooler in a vacuum using 2.0 MPa inlet pressure, the calculations predicted a temperature drop of 57 K and mass flow rate of 19.5 mg/s compared to measured values of 63 K and 19.4 mg/s therefore showing that conventional macroscale correlations can hold well for turbulent microscale flow and heat transfer as long as the validity of the assumptions is verified..
185. Tatsuhiro Mori, Takuhito Otofuji, Hiromi Kubota, Yasuyuki Takata, Masamichi Kohno, The Effects of a Beam Wavelength on Laser Micro Processing of Ceramics, Proceedings of the 21st International Symposium on Transport Phenomena (ISTP-21), Paper No. 228, Kaoshiung City, Taiwan, Nov. 2-5, 2010, 2010.11.
186. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical analysis of heat pumping in oscillatory flows, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.76.771_1924, 76, 771, 1924-1931, 2010.11, A numerical analysis has been performed to clarify how heat pumping in a regenerator is generated in oscillatory flows and to investigate the effect of heat pumping on the phase difference between pressure and velocity. Pulse tube refrigerators of the 1st and 2nd generations are used as physical models in this study. In the 1st generation, the phase difference between pressure and velocity is nearly 90° and in the 2nd generation, nearly 0°. Transient one-dimensional equations of continuity, momentum and energy are solved utilizing a TVD scheme. It was found that heat pumping in a regenerator is shown by analyzing the fields of velocity and temperature of gas elements without thermoacoustic theory. It was also found that heat pumping in a regenerator is enhanced when the phase difference between pressure and velocity is nearly 0°..
187. Adhika Widyaparaga, Masashi Kuwamoto, Atsushi Tanabe, Naoya Sakoda, Hiromi Kubota, Masamichi Kohno, Yasuyuki Takata, Study on a wire-type Joule Thomson microcooler with a concentric heat exchanger, Applied Thermal Engineering, 10.1016/j.applthermaleng.2010.07.007, 30, 16, 2563-2573, 2010.11, This study examines the performance of a wire-type Joule Thomson microcooler utilizing a flexible concentric counterflow heat exchanger. Three gases: C2H4, CO2 and N2 were used separately for trials conducted at inlet pressures ranging from 0.5 MPa to 5 MPa with C2H4 having the best performance. During unloaded tests at an inlet pressure of 2.0 MPa, C2H4 obtained a minimum temperature of 225 K while CO2 obtained a minimum temperature of 232 K. Using CO2 the microcooler was able to maintain a temperature of 273 K at 100 mW heat input and 2 MPa inlet pressure. An inlet pressure of 3 MPa allowed a 550 mW heat input at 273 K. Theoretical performance calculations were conducted and compared to experimental results revealing considerable reduction of microcooler performance due to the presence of heat in-leak. Results have displayed that the JT coefficient of the coolant gas is a more dominant factor than heat transfer properties in determining the performance of the coolant. Due to the microscale of the device, relevant scaling effects were evaluated, particularly entrance effects, surface roughness and axial conduction..
188. Y. Takata, N. Sakoda, K. Shinzato, M. Fujii, Measurement of Hydrogen Thermophysical Properties at Ultra High Pressures, Proceedings of the 9th Asian Thermophysical Properties Conference(KEYNOTE), Beijing, China, Oct. 19-22, 2010, ATPC9-109309, 2010.10.
189. Shogo Moroe, Koichi Kimura, Jun Fukai, Masamichi Kohno, Yasuyuki Takata, Peter L Woodfield, Kan’ei Shinzato, Motoo Fujii, Dependence of Hydrogen Thermal Conductivity on Ortho-Para Composition Ratio, Proceedings of the 9th Asian Thermophysical Properties Conference(KEYNOTE), Beijing, China, Oct. 19-22, 2010, ATPC9- 109077, 2010.10.
190. Naoya Sakoda, Kenta Shindo, Koichi Motomura, Supriatno, Kan’ei Shinzato, Masamichi Kohno, Yasuyuki Takata, Motoo Fujii, Measurement of PVT Property of Hydrogen at High Pressures Up to 100 Mpa and Development of A Virial Equation of State, Proceedings of the 9th Asian Thermophysical Properties Conference(KEYNOTE), Beijing, China, Oct. 19-22, 2010, ATPC9- 109156, 2010.10.
191. Elin Yusibani, Kanei Shinzato, Motoo Fujii, Yosuke Nagahama, Masamichi Kohno, Yasuyuki Takata, Peter L. Woodfiled, Hydrogen Viscosity at 293 to 400K up to 100 MPa with Capillary Tube Method, Proceedings of the 9th Asian Thermophysical Properties Conference(KEYNOTE), Beijing, China, Oct. 19-22, 2010, ATPC9-109172, 2010.10.
192. Adhika Widyaparaga, Masashi Kuwamoto, Naoya Sakoda, Masamichi Kohno, Yasuyuki Takata, Theoretical Study of a Flexible Wiretype Joule Thomson Micro-Refrigerator for Use in Cryosurgery, Proceedings of the Eighth International ASME Conference on Nanochannels, Microchannels and Minichannels(ICNMM2010), ICNMM2009-82215, 2010.08.
193. Masamichi Kohno, Koichi Kimura, Shogo Moroe, Yasuyuki Takata, Peter L. Woodfield, Motoo Fujii, Measurement of effective thermal conductivity of CNT-nanofluids by transient short-wire method, ASME 2009 Micro/Nanoscale Heat and Mass Transfer International Conference 2009, MNHMT2009 Proceedings of the ASME Micro/Nanoscale Heat and Mass Transfer International Conference 2009, MNHMT2009, 10.1115/MNHMT2009-18068, 407-412, 2010.07, Thermal conductivity and thermal diffusivity of CNT-nanofluids and Al 2O3-nanofulids were measured by the transient short-hot-wire method. The uncertainty of their measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. Three different shapes of Al2O3 particles were prepared for Al2O3-water nanofluids. For the thermal conductivity of Al2O3-water nanofluids, there are differences in the enhancement of thermal conductivity for differences in particle shapes. Hardly any enhancement of thermal conductivity was observed for SWCNT-water nanofluids because the volume fraction of SWCNT was extremely low. However, we consider by increasing the volume fraction of SWCNTs, it will be possible to enhance the thermal conductivity..
194. Elin Yusibani,Peter L. Woodfield,新里寛英,河野正道,高田保之,藤井丕夫, 高温高圧水素の粘性係数推算式の提案, 熱物性, 24, 1, 21-27, 2010.03.
195. 迫田直也,進藤健太,新里寛英,河野正道,高田保之,藤井丕夫, 高圧水素用バーネット式PVT性質測定装置の開発, 熱物性, 24, 1, 28-34, 2010.03.
196. N. Sakoda, K. Shindo, K. Shinzato, M. Kohno, Y. Takata, and M. Fujii, Review of the Thermodynamic Properties of Hydrogen Based on Existing Equations of State, International Journal of Thermophysics, 31, 2, 276-296, 2010.02.
197. N. Sakoda, K. Shindo, K. Shinzato, M. Kohno, Y. Takata, M. Fujii, Review of the thermodynamic properties of hydrogen based on existing equations of state, International Journal of Thermophysics, 10.1007/s10765-009-0699-7, 31, 2, 276-296, 2010.02, Currently available equations of state (EOSs) for hydrogen are reviewed, and the data for the critical point, normal boiling point, and triple point are summarized. Through comparisons of PVT, saturated properties, heat capacity, and speed of sound among the latest EOSs for hydrogen, their features are discussed. The proper use of the EOSs, including a consideration of the nuclear isomers (ortho-and parahydrogen), is of great importance, especially for saturated properties, heat capacity, and speed of sound because these properties are different between the nuclear isomers. The present review concludes with recommendations for use of the EOSs for hydrogen..
198. Masamichi Kohno, K. Kimura, S. Moroe, P.L. Woodfield, M. Fujii, Y. Takata, Measurement of effective thermal conductivity of CNTnanofluids by transient short-wire method, Proceedings of the ASME 2009 Micro/Nanoscale Heat and Mass Transfer International Conference, MNHMT2009-18068, 2009.12.
199. Elin Yusibani, Peter Lloyd Woodfield, Shogo Moroe, Kanei Shinzato, Masamichi Kohno, Yasuyuki Takata, Motto Fujii, A procedure for application of the three-omega method to measurement of gas thermal conductivity, Journal of Thermal Science and Technology, 10.1299/jtst.4.146, 4, 1, 146-158, 2009.12, A non-linear least-squares curve-fitting procedure is proposed to analyze three-omega voltage data from a fine wire in a gas sample using the three-omega method. The method uses both three-omega components of the voltage arising from a sinusoidal heating current to determine the thermal conductivity of the surrounding medium. The proposed procedure is tested against simulated data and some experimental data for air at atmospheric pressure. Treating the technique as an absolute method and assuming a known sample heat capacity, the thermal conductivity of air has been measured at room temperature to within 11% of a reference value. Practical application of the method may require a calibrated effective wire length and wire diameter. An average wire temperature rise of around 10 K to ensure the three-omega components is enough for accurate measurement..
200. M. Kohno, A. Tanabe, Y. Kuwamoto, H. Kubota, Y. Takata, Flexible Joule-Thomson micro-refrigerator, 7th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2009 Proceedings of the 7th International Conference on Nanochannels, Microchannels, and Minichannels 2009, ICNMM2009, 10.1115/ICNMM2009-82215, 835-840, 2009.12, In this study, a prototype flexible Joule-Thomson micro-refrigerator was fabricated and its cooling power was examined. The micro-refrigerator uses N2, C2H4 or CO2 as a working gas and it consists mainly of a heat exchanger and an evaporator. The outside diameter of the heat exchanger outer tube is 0.9 mm and that of the inner tube is 0.4 mm. The length of the heat exchanger is 450mm. The inner diameter of the evaporator capillary is 0.1 mm. A cooling power of 100 mW at an evaporator temperature of 277 K was attained for inlet and outlet gas (CO2) pressures of 5.0 MPa and 0.1 MPa, respectively. To understand the cooling performance, a numerical analysis of the heat exchanger has been done and the effects of mass flow rate and dimensions of the heat exchanger on temperature profiles and effectiveness were examined..
201. P. L. Woodfield, S. Moroe, J. Fukai, M. Fujii, K. Shinzato, M. Kohno, Y. Takata, Techniques for accurate resistance measurement in the transient short-hot-wire method applied to high thermal-diffusivity gas, International Journal of Thermophysics, 10.1007/s10765-009-0668-1, 30, 6, 1748-1772, 2009.12, The accuracy of high-speed transient resistance measurements is an important issue particularly for measuring the thermal conductivity of high thermal-diffusivity (low-density) gases. This is because the hot-wire temperature rise against the logarithm of time is non-linear and can approach a steady state within the typical measurement time of 1 s. Two types of voltmeters are compared for use in the transient short-hot-wire method. Details of suitable procedures for taking accurate transient resistance measurements with either a two-channel high-speed analog/digital converter or a pair of integrating digital multimeters are presented..
202. Naoya Sakoda, Kenta Shindo, Kan’ei Shinzato, Masamichi Kohno, Yasuyuki Takata, Motoo Fujii, PVT Measurements of High Pressure Gas by the Burnett Method, Proceedings of the International Conference on Power Engineering (ICOPE-09), 2009.11.
203. Y. Takata, P.L. Woodfield, N. Sakoda, K. Shinzato and M. Fujii, Measurement of Hydrogen Thermophysical Properties at High Pressure, The Eleventh UK National Heat Transfer Conference (UKHTC2009), Keynote Lecture, London, 2009.09.
204. M. Kohno, A. Widyaparaga, A. Tanabe, M. Kuwamoto, H. Kubota and Y. Takata, Joule-Thomson micro-refrigerator with flexible regenerative heat exchanger, Proceedings of the Seventh International Conference on Enhanced, Compact and Ultra-Compact Heat Exchangers: From Microscale Phenomena to Industrial Applications, Heredia, Costa Rica, 2009.09.
205. Masamichi Kohno, Shinji Kawauchi, Takuhito Otofuji, Yasuyuki Takata, Laser Micro Grooving of Aluminum Nitride, Proceedings of the 20th International Symposium on Transport Phenomena, Victoria, Canada, 2009.07.
206. E. Yusibani, P. L. Woodfield, S. Moroe, K. Shinzato, M. Kohno and Y. Takata and M. Fujii, A Procedure for Application of the Three-Omega Method to Measurement of Gas Thermal Conductivity, Journal of Thermal Science and Technology, Vol.4, No.1, pp.146-158, 2009 June, 2009.06.
207. P. L. Woodfield, J. Fukai, M. Fujii, Y. Takata, An Accelerated Two-Dimensional Unsteady Heat Conduction Calculation Procedure for Thermal-Conductivity Measurement by the Transient Short-Hot-Wire Method, International Journal of Thermophysics, Vol.30, No.3, pp.796-809, 2009.06.
208. E. Yusibani, P. L. Woodfield, M. Kohno, K. Shinzato, Y. Takata, M. Fujii, End Effects in the Three-Omega Method to Measure Gas Thermal Conductivity, International Journal of Thermophysics, Vol.30, No.3, pp.833-850, 2009.06.
209. M. Kohno, A. Tanabe, Y. Kuwamoto, H. Kubota & Y. Takata, Flexible Joule‐Thompson Micro-Refrigerator, Proceedings of the Seventh International ASME Conference on Nanochannels, Microchannels and Minichannels, ICNMM2009-82215, 2009.06.
210. P. L. Woodfield, J. Fukai, M. Fujii, Y. Takata, An accelerated two-dimensional unsteady heat conduction calculation procedure for thermal-conductivity measurement by the transient short-hot-wire method, International Journal of Thermophysics, 10.1007/s10765-009-0583-5, 30, 3, 796-809, 2009.06, A fast and accurate procedure is proposed for solution of the two-dimensional unsteady heat conduction equation used in the transient short-hot-wire method for measuring thermal conductivity. Finite Fourier transforms are applied analytically in the wire-axis direction to produce a set of one-dimensional ordinary differential equations. After discretization by the finite-volume method in the radial direction, each one-dimensional algebraic equation is solved directly using the tri-diagonal matrix algorithm prior to application of the inverse Fourier transform. The numerical procedure is shown to be very accurate through comparison with an analytical solution, and it is found to be an order of magnitude faster than the usual numerical solution..
211. E. Yusibani, P. L. Woodfield, M. Kohno, K. Shinzato, Y. Takata, M. Fujii, End effects in the three-omega method to measure gas thermal conductivity, International Journal of Thermophysics, 10.1007/s10765-009-0572-8, 30, 3, 833-850, 2009.06, A two-dimensional analytical solution is derived for the three-omega method for measurement of thermal conductivity of materials with a fine wire. The analytical solution includes the wire heat capacity and the effect of heat losses from the ends of the wire. To derive the solution, finite Fourier transforms are applied in the direction parallel to the wire axis. The solution is compared with a one-dimensional solution and experimental data. It is found that heat losses from the wire ends have a significant effect on the 3ω components at low frequency and tend to be less important at high frequency. Moreover, it is shown that two-dimensional effects will be severe for nano-scale wires, even if the wire length-to-diameter ratio is very large..
212. Yasuyuki Takata, Sumitomo Hidaka, Masamichi Kohno, Wettability improvement by plasma irradiation and its applications to phase-change phenomena, Heat Transfer Engineering, 10.1080/01457630802594820, 30, 7, 549-555, 2009.06, Plasma irradiation is one of the techniques to improve surface wettability. This technique can be used to enhance heat transfer of liquid-vapor phase change. For instance, evaporation of a water droplet can be enhanced by plasma irradiation. The relation between plasma irradiation time and contact angle was examined first for three metals and then the lifetime of a water drop on a hot surface was measured changing the surface wettability by plasma irradiation. The lifetime of the water drop decreased and the wetting limit temperature increased with the increasing irradiation time of plasma. Hydrophilicity by plasma irradiation is not a permanent effect but it will be useful for enhancement of cooling of hot metal..
213. Y. Takata, S. Hidaka, M. Kohno, N. Ishihara, K. Tagashira, T. Kuroki, Behavior of Small Water Droplets Impinging onto a Hot Surface –Effects if Surface Roughness and Impinging Velocity, Proceedings of the 7th ECI International Conference on Boiling Heat Transfer, Florianopolis, Brazil, May 3-7, 2009, 2009.05.
214. E. Yusibani, P. L. Woodfield, M. Fujii, K. Shinzato, X. Zhang and Y. Takata, Application of the Three-Omega Method to Measurement of Thermal Conductivity and Thermal Diffusivity of Hydrogen Gas, International Journal of Thermophysics, Vol.30, No.2, pp.397-415, 2009.04.
215. E. Yusibani, P. L. Woodfield, M. Fujii, K. Shinzato, X. Zhang, Yasuyuki Takata, Application of the three-omega method to measurement of thermal conductivity and thermal diffusivity of hydrogen gas, International Journal of Thermophysics, 10.1007/s10765-009-0563-9, 30, 2, 397-415, 2009.04, Preliminary investigations have been conducted to discuss the possibility of measuring the thermal conductivity of hydrogen gas by the three-omega method. A one-dimensional analytical solution for the 3ω component is derived which includes the effect of the wire heat capacity. It is shown that it is very important to take into account the wire heat capacity in the calculation to measure the thermal conductivity of gas by the three-omega method. In contrast, the wire heat capacity is less important for the thermal conductivity of the liquid or solid phase. The importance of the wire heat capacity is found to increase with increasing frequency and decrease if the sample thermal conductivity is high. In order to measure the thermal conductivity of hydrogen gas at atmospheric pressure, a wire of diameter less than 1μm is necessary if the properties of the wire are to be neglected..
216. Masamichi Kohno, Takashi Nishizono, Yasunori Onaka, Sumitomo Hidaka, Koji Takahashi, Yasuyuki Takata, Micro oscillation heat pipe fabricated on silicon wafer, 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008 Proceedings of the 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, 10.1115/ICNMM2008-62082, 1343-1346, 2008.12, Heat transport characteristics of micro oscillation heat pipe have been investigated. A single winding flow path consists of 28 turns microchannels fabricated on a silicon wafer the size of which was 31mmx27mm. We used heat pipe with non-uniformed cross section. Equivalent diameters of channels were 0.19 and 0.10mm. Test fluid was R141b and liquid fractions were 0, 75, 85%. It was found that steady pulsating flow occurred by increasing the number of turns and the frequency of vibration has an effect on heat transfer performance..
217. Peter L. Woodfield, 深井潤,藤井丕夫,高田保之,新里寛英, 非定常短細線熱伝導セル内の短細線周りの自然対流の数値シミュレーション, 熱物性, Vol.22, No.4, pp.217-222, 2008.10.
218. N. Sakoda, K. Shinzato, M. Kohno, Y. Takata, M. Fujii, Development of PVT Measurement Apparatus and Preliminary Measurements for Hydrogen , Proceedings of the 18th European Conference on Thermophysical Properties, 2008.09.
219. Y. Takata, S. Hidaka, A. Okabe, M. Kohno, Y. Shigesato, G. Hayase, Wettability Effect in Condensation on Fin Surface, Proceedings of the 19th International Symposium on Transport Phenomena, 2008.08.
220. P. L. Woodfield, J. Fukai, M. Fujii, Y. Takata, K. Shinzato, A two-dimensional analytical solution for the transient short-hot-wire method, International Journal of Thermophysics, 10.1007/s10765-008-0469-y, 29, 4, 1278-1298, 2008.08, Unlike the conventional transient hot-wire method for measuring thermal conductivity, the transient short-hot-wire method uses only one short thermal-conductivity cell. Until now, this method has depended on numerical solutions of the two-dimensional unsteady heat conduction equation to account for end effects. In order to provide an alternative and to confirm the validity of the numerical solutions, a two-dimensional analytical solution for unsteady-state heat conduction is derived using Laplace and finite Fourier transforms. An isothermal boundary condition is assumed for the end of the cell, where the hot wire connects to the supporting leads. The radial temperature gradient in the wire is neglected. A high-resolution finite-volume numerical solution is found to be in excellent agreement with the present analytical solution..
221. P. L. Woodfield, Jun Fukai, M. Fujii, Yasuyuki Takata, K. Shinzato, Determining thermal conductivity and thermal diffusivity of low-density gases using the transient short-hot-wire method, International Journal of Thermophysics, 10.1007/s10765-008-0468-z, 29, 4, 1299-1320, 2008.08, The transient short-hot-wire method for measuring thermal conductivity and thermal diffusivity makes use of only one thermal-conductivity cell, and end effects are taken into account by numerical simulation. A search algorithm based on the Gauss-Newton nonlinear least-squares method is proposed to make the method applicable to high-diffusivity (i.e., low-density) gases. The procedure is tested using computer-generated data for hydrogen at atmospheric pressure and published experimental data for low-density argon gas. Convergence is excellent even for cases where the temperature rise versus the logarithm of time is far from linear. The determined values for thermal conductivity from experimental data are in good agreement with published values for argon, while the thermal diffusivity is about 10 % lower than the reference data. For the computer-generated data, the search algorithm can return both thermal conductivity and thermal diffusivity to within 0.02 % of the exact values. A one-dimensional version of the method may be used for analysis of low-density gas data produced by conventional transient hot-wire instruments..
222. Deendarlianto, Y. Takata, S. Hidaka, M. Kohno, The effect of contact angle on the evaporation of water droplet on a heated solid surface, Proceedings of the 5th International Conference on Transport Phenomena in Multiphase Systems, 2008.06.
223. M. Kohno, T. Nishizono, Y. Onaka, S. Hiaka, K. Takahashi and Y. Takata, Micro Oscillation Heat Pipe Fabricated on Silicon Wafer, Proceedings of ASME ICNMM2008: 6th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2008-62082, 2008.06.
224. P. L. Woodfield, J. Fukai, M. Fujii, Y. Takata, K. Shinzato, Estimation of Raefied Gas Effects on Thermal Conductivity of Hydrogen in a Transient-Hot-Wire Cell, Proceedings of the 17th World Hydrogen Energy Conference, 2008.05.
225. Y. Takata, K. Sugahara, T. Tachikawa, S. Moroe, H. Kubota, M. Kohno, K. Takahashi, T. Koshimizu, Micro-refrigerator fabricated on silicon wafer, 5th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2007 Proceedings of the 5th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2007, 10.1115/ICNMM2007-30108, 749-754, 2007.12, A prototype Joule-Thomson micro-cooler was fabricated on silicon wafer by making use of photofabrication. The microcooler uses ethylene as a refrigerant and it consists mainly of heat exchanger and evaporator. The cooling power of 20mW at evaporator temperature of 272K was attained at the inlet and outlet gas pressures of 2.5MPa and 0.1MPa, respectively. To understand the low cooling performance, numerical analysis of heat exchanger has been done and the effects of mass flow rate and thermal conductivity of solid on temperature profiles and effectiveness were examined. It was found that the flow rate of present experiment is too large and the decrease in flow rate gives better temperature effectiveness of heat exchanger. It was also found that the low thermal conductivity of solid improves the performance of heat exchanger..
226. Peter L. Woodfield, Shogo Moroe, Jun Fukai, Motoo Fujii, Masamichi Kohno, Yasuyuki Takata, Ka N.Ei Shinzato, Numerical simulation for design of probe to measure hydrogen thermal conductivity at high pressure by the transient short-wire method, Memoirs of the Faculty of Engineering, Kyushu University, 67, 4, 209-220, 2007.12, Hydrogen energy is expected to be a next generation clean energy. However there are still many issues that must be overcome before commercializing hydrogen energy. Clarifying the mechanism for the effects of hydrogen on all types of materials and understanding the characteristics of hydrogen at high temperature and high pressure are indispensable. This study focuses on the development of the measurement technique for the thermal conductivity of hydrogen in the high pressure and the high temperature region. Numerical simulations are performed to investigate the effect of wire diameter, length and vessel size in a short-wire thermal conductivity probe designed for the study of hydrogen gas in the range of pressures from 0.1 to 100 MPa and temperatures from 25 to 500°C. The two-dimensional unsteady heat conduction equation is discretized using the finite volume method to calculate the thermal field. The influence of the natural convection was examined using an empirical equation from the literature. The size of the vessel, the wire diameter, and the wire length respectively were changed within the range of R=2.5-50mm, d=5-50μm, and H=20-160mm..
227. Takao Koshimizu, Yasuyuki Takata, Hiromi Kubota, Takehiro Ito, Numerical simulation of heat pumping in a pulse tube refrigerator, 2007 ASME/JSME Thermal Engineering Summer Heat Transfer Conference, HT 2007 2007 Proceedings of the ASME/JSME Thermal Engineering Summer Heat Transfer Conference - HT 2007, 10.1115/HT2007-32729, 715-720, 2007.12, Numerical simulation of heat and fluid flow in a basic and an orifice pulse tube refrigerator have been performed to visualize heat pumping generated in the regenerator and the pulse tube, and to clarify the difference in heat pumping caused by the phase difference between pressure and displacement of gas. Common components of the regenerator and the pulse tube are used in the basic and the orifice pulse tube refrigerator. The flow in the tube is assumed to be one-dimensional and compressible. As governing equations, the continuity, momentum and energy equations are used in this study. From the temperature and velocity field obtained as a result of the simulation, the relation between the displacement and the temperature change of gas elements is visually clarified, and consequently it is found that the characteristic that the temperatures of gas elements are nearly higher than those of the regenerator material or the pulse-tube wall during compression and lower during expansion is very important for the heat pumping in basic and orifice pulse tube refrigerators. Furthermore, the behavior of heat pumping in the basic and the orifice pulse tube refrigerator is illustrated by analyzing the relation between the displacement of gas elements and heat quantity transferred to the wall from the gas elements, and the difference in heat pumping between the basic and the orifice pulse tube refrigerator is made clear..
228. Soma Yamamoto, Yasumori Onaka, Shinzo Suzuki, Shigeo Maruyama, Keita Tani, Yasuyuki Takata, Yasushi Shibuta, Masamichi Kohno, Synthesis of single walled carbon nanotubes by laser vaporized catalytic chemical vapor deposition technique, 2007 ASME/JSME Thermal Engineering Summer Heat Transfer Conference, HT 2007 2007 Proceedings of the ASME/JSME Thermal Engineering Summer Heat Transfer Conference - HT 2007, 10.1115/HT2007-32776, 387-393, 2007.12, SWNTs were synthesized by laser vaporized CCVD (Catalytic Chemical Vapor Deposition). The diameter distribution and the purity of SWNTs synthesized at different temperatures, laser intensities and catalysts were investigated by Raman spectroscopy. Both of them tended to shift towards a larger area as reacting temperature or laser intensity was increased. Ni, Co and Fe played a catalytic role, though Ag and Cu were less effective at our experimental conditions. In addition, the conventional laser oven technique and laser vaporized CCVD technique were also compared. The diameter distribution of SWNTs which were synthesized by the conventional laser oven technique was narrower than that of SWNTs synthesized by the laser vaporized CCVD technique..
229. Yasuyuki Takata, The heat transfer family of Kyushu university, Heat Transfer Engineering, 10.1080/01457630701483463, 28, 12, 968-972, 2007.12, Kyushu University has been one of the most active universities in heat transfer research, especially in the field of boiling and condensation. The heat transfer research in Kyushu University was initiated by Prof. K. Yamagata about 75 years ago. He brought up a number of heat transfer professors including Prof. K. Nishikawa and his successors, and his group has been called the "Heat Transfer Family." The present article introduces its history and the current status of heat transfer research in Kyushu University..
230. Y. Takata, N. Sakoda, K. Shinzato, K. Fujii, M. Fujii, Research Project of Hydrogen Thermophysical Properties at Ultra High Pressure, Proceedings of the Sixth International Conference on Enhanced, Compact and Ultra-Compact Heat Exchangers: Science, Engineering and Technology, Keynote Lecture, 2007.09.
231. Y. Takata, Surface Wettability Effects in Liquid-Vapor Phase Change, Proceedings of the 18th International Symposium on Transport Phenomena, Keynote Lecture 4, ISTP18-164, 2007.08.
232. Tomohiko Yamaguchi, Satoru Momoki, Ryo Akasaka, Tomohiro Honda, Yasuyuki Takata, Takehiro Ito, Program Package for Thermophysical Properties of Fluids: PROPATH - A New Implementation of the VTPR Equation of State –, Proceedings of the 8th Asian Thermophysical Properties Conference, Paper No.266, 2007.08.
233. Naoya Sakoda, Elin Yusibani, Peter Lloyd Woodfield, Kan'ei Shinzato, Masamichi Kohno, Yasuyuki Takata, Motoo Fujii, Review of Thermophysical Properties of Hydrogen and the Related Work of HYDROGENIUS, Proceedings of the 8th Asian Thermophysical Properties Conference, Paper No.178, 2007.08.
234. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical Simulation of Heat Pumping in a Pulse Tube Refrigerator, Proceedings of HT2007: 2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference, HT2007-32729, 2007.07.
235. Y. Takata, S. Hidaka and M. Kohno, Wettability Improvement by Plasma Irradiation and its Applications to Phase Change Phenomena, Proceedings of the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics-HEFAT2007, Paper No. K1, 2007 (KEYNOTE), 2007.06.
236. Shohei Chiashi, Masamichi Kohno, Yasuyuki Takata, Shigeo Maruyama, Localized synthesis of single-walled carbon nanotubes on silicon substrates by a laser heating catalytic CVD, Journal of Physics: Conference Series, 10.1088/1742-6596/59/1/033, 59, 1, 155-158, 2007.04, Synthesis of high-purity single-walled carbon nanotubes (SWNTs) is demonstrated by a laser heating catalytic CVD method. This method makes it possible to produce SWNTs without the use of an electric furnace or hot filament. SWNTs were synthesized from alcohol using Fe/Co catalyst particles supported on zeolite and Mo/Co particles deposited directly on a substrate. Synthesis of high purity SWNTs was confirmed by in situ Raman scattering analysis and AFM and FE-SEM observations..
237. S. Chiashi, M. Kohno, Y. Takata and S. Maruyama, Localized synthesis of single-walled carbon nanotubes on silicon substrates by a laser heating catalytic CVD, Journal of Physics: Conference Serie, in press, 2006.12.
238. Sumitomo Hidaka, Akimitsu Yamashita, Yasuyuki Takata, Effect of contact angle on wetting limit temperature, Heat Transfer - Asian Research, 10.1002/htj.20128, 35, 7, 513-526, 2006.11, The effect of surface wettability on evaporation of a water drop has been examined experimentally using surfaces with various contact angles. To greatly change the surface wettability, TiO2 superhydrophilicity, plasma irradiation, and super-water-repellent surface are adopted as the heating surface. The range in contact angle achieved by these methods was between 0° and 170°. The relationship between the contact angle and the wetting limit temperature was obtained and it was found that the lifetime of a water drop dramatically decreases with contact angle in the lower temperature region, and that the wetting limit temperature increases with the contact angle..
239. Yasuyuki Takata, Sumitomo Hidaka, Takashi Uraguchi, Boiling Feature on a Super Water-Repellent Surface, Heat Transfer Engineering, Vol.27, No.8, pp.25-30, 2006.10.
240. Sumitomo Hidaka, Akimitsu Yamashita, Yasuyuki Takata, Effect of Contact Angle on Wetting Limit Temperature, Heat Transfer-Asian Research, Vol.35, No.7, pp.513-526, 2006.10.
241. Xiu-Tian Zhao, Kenji Sakka, Naoto Kihara, Yasuyuki Takata, Makoto Arita, Masataka Masuda, Hydrophilicity of TiO2 thin films obtained by RF magnetron sputtering deposition, Current Applied Physics, Vol.6, No.5, pp.931-933, 2006.09.
242. S. Kawauchi, M. Kohno, Y. Takata and Y. Matsuoka, Microdrilling in Thin Metal Foils with a Nanosecond Pulsed Bessel Laser Beam, Proceedings of the 17th International Symposium on Transport Phenomena, CD-ROM, 2006.09.
243. Yasuyuki Takata, Sumitomo Hidaka, Takashi Uraguchi, Boiling feature on a super water-repellent surface, Heat Transfer Engineering, 10.1080/01457630600793962, 27, 8, 25-30, 2006.09, The boiling feature on a super water-repellent (SWR) surface has been studied. The SWR surface has a coating layer of fine particles of nickel and PTFE. Its contact angle to water is 152° in room temperature. The heat transfer surface is facing upward, and the diameter of the heated section is 17 mm. The boiling feature of this surface is completely different from that of usual surfaces. The stable film boiling occurs in very small superheating, and there is no nucleate boiling region. The bubbles generated on the surface coalesce into a vapor film without departing from the surface. The stable vapor film exists even at a surface temperature below the saturation temperature..
244. Xiu Tian Zhao, Kenji Sakka, Naoto Kihara, Yasuyuki Takata, Makoto Arita, Masataka Masuda, Hydrophilicity of TiO2 thin films obtained by RF magnetron sputtering deposition, Current Applied Physics, 10.1016/j.cap.2005.01.042, 6, 5, 931-933, 2006.09, Titanium dioxide thin films were deposited on stainless steel substrates by radio frequency (RF) magnetron sputtering method. The relative humidity (RH) and oxygen content of the environment were varied systematically. The hydrophilicity of the films under ultraviolet (UV) irradiation was investigated. It was found that the hydrophilicity of the films was strongly affected by the RH and the oxygen content of the environment. This would be attributable to the adsorption of oxygen and hydroxyl group and the recombination of the electron-hole pair would be affected by the adsorbed species too. In the X-ray photoelectron spectroscopy (XPS) experiment, we succeeded in measuring the effect of UV irradiation using helium light source of ultraviolet photoelectron spectroscopy (UPS). The XPS analysis revealed that under UV irradiation, Ti3+ was produced and the adsorption of hydroxyl groups on the surface of TiO2 films was increased. The titanium dioxide films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM)..
245. M. Kohno, S. Kawauchi, Y. Takata, Y. Matsuoka, Microdrilling of Metals with a Nano-Second Pulsed Bessel Laser Beam, Proceedings of the 13th International Heat Transfer Conference, Sydney, CD-ROM, 2006.08.
246. T. Yamaguchi, R. Akasaka, T. Honda, S. Momoki, T. Takata and T. Ito, Development of Program Package for Thermophysical Properties of Fluids: PROPATH- Availabilities of Dynamic Link Library (DLL) in Windows Applications, Proceedings of the 16th Symoposium on Thermophysical Properties, Boulder, CO, USA, CD-ROM, 2006.07.
247. Y. Takata, Surface Wettability Effects in Heat and Fluid Flow, Proceedings of the 4th International Conference on Nanochannels, Microchannels and Minichannels, Paper No. ICNMM2006-96031, 2006.06.
248. Y. Takata, S. Hidaka, M. Kohno, Enhanced Nucleate Boiling by Superhydrophilic Coating with Checkered and Spotted Patterns, Proceedings of the 6the International Conference on Boiling Heat Transfer, 2006.05.
249. 35. Xiu-Tian Zhao, Kenji Sakka, Naoto Kihara, Yasuyuki Takata, Makoto Arita, Masataka Masuda, Hydrophilicity of TiO2 thin films obtained by RF magnetron sputtering deposition, Current Applied Physics, Vol.6, No.5, pp. 931-933, 2006.01.
250. Yasuyuki Takata, Surface wettability effects in heat and fluid flow, 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006 Proceedings of the 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, 2006 B, 1333-1341, 2006, Effects of surface wettability on liquid-vapor phase change phenomena and single- and two-phase flow in tube have been studied in wide range of contact angles using superhydrophilic (SH) and super-water-repellent (SWR) surfaces. Heat transfer in falling film evaporation on a TiO2-coated SH surface is tremendously enhanced due to very thin stable film. In pool boiling, critical heat flux (CHF) and minimum heat flux (MHF) increase with the decrease in contact angle. Wetting limit temperature of water drop on heated surface increases with the decrease in contact angle. In pool boiling on SWR surface, bubble nucleation and film boiling occur in extremely small superheating. Drag reduction was observed in water flow in tube with SWR coating in laminar flow region, and on the other hand, in two-phase flow pressure drop for the SH wall is smaller than that for the SWR wall..
251. Takao Koshimizu, Yasuyuki Takata, Daisaku Kasao, Masanori Monde, Thermal analysis on filling process in hydrogen tank, 2005 ASME International Mechanical Engineering Congress and Exposition, IMECE 2005 Proceedings of the ASME Heat Transfer Division 2005, 10.1115/IMECE2005-80840, 141-148, 2005.12, When hydrogen is filled into a hydrogen tank, it is considered that the gas temperature in the tank rises considerably because the gas is pressurized to very high pressure. If the ultimate pressure is constant, the gas temperature is influenced by the heat exchange between the gas and the inner wall of the tank, filling time and filling methods. In this research, a numerical analysis of heat and fluid flow has been performed to investigate the behavior of pressure and gas temperature in the tank during and after the filling process when an adiabatic wall and an isothermal wall are variously arranged for each wall that composed the hydrogen tank. As a result, it is found that using an isothermal wall for the wall of the circumference is very effective to cooling of the gas in the tank. In addition, a numerical analysis considering the heat capacity of the wall and the heat exchange between the gas and the inner wall of the tank has been performed to clarify the behavior of pressure and gas temperature in the tank and wall temperature of the tank under a more realistic condition, and to compare its result with the numerical results under the condition in which an adiabatic wall and an isothermal wall are variously arranged. As a result, it is found that the behavior of pressure and gas temperature under the more realistic condition is very similar to those under the condition in which an isothermal wall is used for the wall of the circumference, and consequently when the behavior for a short time is shown, realistic behavior in the tank can be clarified even under the condition of an isothermal wall because the change in wall temperature is very small. Finally, the change in wall temperature under the more realistic condition is shown and consequently the behavior of the small increase of the wall temperature is clarified..
252. Takao Koshimizu, HiroDaisaku Kasao, Yasiyuki Takata, Masanori Monde, Thermal Analysis on Filling Process in Hydrogen Tank, Proceedings of IMECE2005: 2005 ASME International Mechanical Engineering Congress and Exposition, MECE2005-80840, 2005.11.
253. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical Simulation of Heat and Fluid Flow in Basic Pulse Tube Refrigerator, International Journal of Numerical Methods for Heat & Fluid Flow, 10.1108/09615530510613843, 15, 7, 617-630, Vol.15, No.7, pp.617-630, 2005.10.
254. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical simulation of heat and fluid flow in basic pulse tube refrigerator, International Journal of Numerical Methods for Heat and Fluid Flow, 10.1108/09615530510613843, 15, 7, 617-630, 2005.10, Purpose - To clarify the physical working principle of refrigeration in basic pulse tube refrigerators (BPTRs). Design/methodology/approach - A numerical simulation was performed. Transient compressible NS equation was solved utilizing the TVD scheme coupled with energy equation. Findings - The periodic flow and temperature field were obtained. The movement of the gas particles and heat transfer between the gas particles and wall were analyzed. These numerical results explained the mechanism of surface heat pumping (SHP) which is known as the working principle of refrigeration in BPTR. Research limitations/implications - Pulse tube refrigerator (PTR) is classified into the third generation. BPTR is the first generation. It is needed to clarify the working principle of refrigeration in the second and third generation by analyzing heat and fluid flow in the tube. Practical implications - A very useful source of information to understand the physical working principle of refrigeration in BPTR. Originality/value - The mechanism of SHP was shown by analyzing the heat exchange between the gas particles and pulse tube wall..
255. Y. Takata, S. Hidaka and M. Kohno, Boiling from a Super-Water-Repellent Surface, Proceedings of the Fifth International Conference on Enhanced, Compact and Ultra-Compact Heat Exchangers: Science, Engineering and Technology, 2005.09.
256. Sumitomo Hidaka, Akimitsu Yamashita, Yasuyuki Takata, Effect of contact angle on wetting limit temperature, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.71.2309, 71, 709, 2309-2315, 2005.09, Effect of surface wettability on evaporation of water drop has been examined experimentaly using surfaces with various contact angles. To change widely the surface wettability, TiO2 superhydrophilicity, plasma irradiation and super-wate-reppllent surface are adopted as the heating surface. The range in contact angle achieved by these methods was between 0° and 170°. The relationship between the contact angle and the wetting limit temperature were obtained and it was found that the lifetime of water drop dramatically decreases with contact angle in lower temperature region, and that the wetting limit temperature increases with contact angle..
257. Y. Takata, Effect of Surface Wettability on Phase Change Phenomena, Proceedings of the HARFKO 2005 International Symposium, pp.3-7, 2005.05.
258. Y. Takata, S. Hidaka and M. Kohno, Boiling Heat Transfer from a Super-Water-Repellent Surface, Proceedings of the 6th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, 2005.04.
259. Xiu-Tian Zhao, Kenji Sakka, Naoto Kihara, Yasuyuki Takada, Makoto Arita, Masataka Masuda, Structure and photo-induced features of TiO2 thin films prepared by RF magnetron sputtering, Microelectronics Journal, 10.1016/j.mejo.2005.02.094, 36, 3-6, 549-551, Vol.30, pp.549-551, 2005.03.
260. Xiu Tian Zhao, Kenji Sakka, Naoto Kihara, Yasuyuki Takata, Makoto Arita, Masataka Masuda, Structure and photo-induced features of TiO2 thin films prepared by RF magnetron sputtering, Microelectronics Journal, 10.1016/j.mejo.2005.02.094, 36, 3-6, 549-551, 2005.03, TiO2 thin films were deposited on stainless steel substrates by radio frequency (RF) magnetron sputtering. The process conditions, including RF power, oxygen partial pressure, and temperature of substrate, were varied systematically. The deposited titanium dioxide films consisted of polycrystalline structure with the mixture of anatase and rutile. The average particle diameter of films changed from dozens of nanometers to hundreds of nanometers. It was found that the conditions, 200 W RF power, 90% oxygen partial pressure, and 673 K temperature of substrate, were optimal to deposit a TiO2 thin film with good photocatalytic activity and photo-induced hydrophilicity that will be attributable to their higher content of anatase..
261. Y. Takata, S. Hidaka, J.M. Cao, T. Nakamura, H. Yamamoto, M. Masuda, T. Ito, Effect of surface wettability on boiling and evaporation, Energy, The International Journal, 10.1016/j.energy.2004.05.004, 30, 2-4, 209-220, Vol.30, Issue 2, pp.209-220, 2005.02.
262. Y. Takata, S. Hidaka, J. M. Cao, T. Nakamura, H. Yamamoto, M. Masuda, T. Ito, Effect of surface wettability on boiling and evaporation, Energy, 10.1016/j.energy.2004.05.004, 30, 2-4 SPEC. ISS., 209-220, 2005.01, Titanium dioxide, TiO2, is one of the photocatalysts that has a very unique characteristic. The surface coated with TiO2 exhibits extremely high affinity for water by exposing the surface to UV light and the contact angle decreases nearly to zero. On the contrary, the contact angle increases when the surface is shielded from UV light. We applied this superhydrophilic nature to enhancement of boiling and evaporation heat transfer. Experiments of pool boiling and evaporation of single water droplet have been performed to manifest the effect of high wettability on heat transfer characteristics. Both of TiO2-coated and non-coated surfaces were used for comparison in each experiment. It is found that (1) the critical heat flux (CHF) of TiO2-coated surface is about two times larger than that of non-coated one, and (2) Leiden-frost temperature increases as the contact angle decreases. The superhydrophilic surface can be an ideal heat transfer surface..
263. K. Naganuma, Yasuyuki Takata, H. Kubota, Koji Takahashi, Study on Joule-Thomson micro-cooler, Proceedings of the Second International Conference on Microchannels and Minichannels (ICMM2004) Proceedings of the Second International Conference on Microchannels and Minichannels (ICMM2004), 769-772, 2004.09, An experimental model of Joule-Thomson micro-cooler has been fabricated on silicone wafer of 39mm×15.5mm in size. The micro-cooler uses ethylene as the refrigerant and it works in the pressure range between 2.3MPa and 0.1MPa. The micro-cooler consists of condenser, evaporator and capillary tube. Flow passage of the refrigerant was fabricated by etching process. Peltier device was used to pre-cool and condense the refrigerant. Temperature decrease by 3K was obtained at maximum flow rate of 3mg/s..
264. T. Koshimizu, H. Kubota, Y. Takata and T.Ito, Numerical Simulation of Heat and Fluid Flow in a Basic Pulse-Tube Refrigerator, Proceedings of the 2004 ASME Heat Transfer/Fluids Engineering Summer Conference, HT-FED2004-56295, 2004.07.
265. Y. Takata, S. Hidaka and T. Uraguchi, Boiling Feature on a Super-water-repllent Surface, Proceedings of the 2nd International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics-HEFAT2003-(CD-ROM), Paper No.TY1, 2004.06.
266. K. Naganuma, Y. Takata, H. Kubota and K. Takahashi, Study on Joule-Thomson Micro-cooler, Proceedings of the 2nd International Conference on Microchannels and Minichannels (ICMM2004), pp.769-772, 2004.06.
267. Y. Takata, S. Hidaka, A. Yamashita and H. Yamamoto, Evaporation of Water Drop on a Plasma-irradiated Hydrophilic Surface, International Journal of Heat and Fluid Flow, 10.1016/j.ijheatfluidflow.2003.11.008, 25, 2, 320-328, Vol.25, No.2, pp.320-328, 2004.04.
268. Y. Takata, S. Hidaka, A. Yamashita, H. Yamamoto, Evaporation of water drop on a plasma-irradiated hydrophilic surface, International Journal of Heat and Fluid Flow, 10.1016/j.ijheatfluidflow.2003.11.008, 25, 2, 320-328, 2004.04, Experimental study has been performed on evaporation of water droplet on stainless steel, copper, and aluminum surfaces. These surfaces are exposed by the plasma irradiation to increase the wettability. We obtained the relation between the plasma irradiation and contact angle first, and then measured the evaporation time, the wetting limit temperature and the Leidenfrost temperature, increasing the surface temperature. The effect of plasma irradiation on evaporation curve has been examined. It is found that the evaporation time decreases and the wetting limit and the Leidenfrost temperatures increase as the contact angle decreases..
269. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical Analysis of Heat and Fluid Flow in Pulse Tube Refrigerator, JSME International Journal, Series B, 10.1299/jsmeb.46.572, 46, 4, 572-578, Vol.46, No.4, pp.572-578, 2003.11.
270. Y. TAKATA, H. SHIRAKAWA, K. TANAKA, T. ITO, Numerical Study on Motion of a Single Bubble Exerted by Non-uniform Electric Field, International Journa of Transport Phenomena, Vol.5, No.4, pp.247-258, 2003.11.
271. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical analysis of heat and fluid flow in pulse tube refrigerator, JSME International Journal, Series B: Fluids and Thermal Engineering, 10.1299/jsmeb.46.572, 46, 4, 572-578, 2003.11, A numerical study has been performed to analyze the working principle of refrigeration in basic pulse tube refrigerator. There is a mechanism called "surface heat pumping" as one of the working principles of refrigeration for basic pulse tube refrigerator of the first generation. This is the mechanism that heat is pumped from the cold end to the hot end by the successive heat exchange between the pulse tube wall and the working gas. Transient axisymmetric two-dimensional equations of continuity, momentum and energy were solved by means of TVD scheme. The transient behaviors of pressure and gas temperature, and heat transfer from the working gas to the tube wall are analyzed. Also the behavior of surface heat pumping is explained by analyzing the axial movements and temperature changes of gas particles..
272. Y. Takata, S. Hidaka, M. Masuda and T. Watanabe, Superhydrophilic Heat Transfer Surface Coated with Titania by RF-Magnetron Sputtering, Proceedings of the 8th UK National Heat Transfer Conference, Oxford (CD-ROM), 2003.09.
273. Y. Takata, S. Hidaka, A. Yamashita, H. Yamamoto, Improvement of Surface Wettability by Plasma Irradiation, Proceedings of the Fourth Interenational Conference on Compact Heat Exchangers and Enhancement Technology for the Process Industries, Crete Island, Greece, pp.305-309, 2003.09.
274. Y. Takata, S. Hidaka, A. Yamashita and H. Yamamoto, Plasma-irradiated Hydrophilic Surfaces and its Applications to Phase Change Heat Transfer, Proceedings of the 2nd International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics-HEFAT2003-(CD-ROM), Paper No.TY1, 2003.06.
275. Takao Koshimizu, Hiromi Kubota, Yasuyuki Takata, Takehiro Ito, Numerical Analysis of Heat and Fluid Flow in Pulse Tube Refrigerator, Numerical Analysis of Heat and Fluid Flow in Pulse Tube Refrigerator, Paper No.TED-AJ03-164, 2003.03.
276. Y. Takata, S. Hidaka, A. Yamashita and H. Yamamoto, Evaporation of Water Drop on a Plasma-irradiated Hydrophilic Surface, Proceedings of the 5th International Boiling Heat Transfer Conference, 10.1016/j.ijheatfluidflow.2003.11.008, 25, 2, 320-328, 2003.03.
277. Y.Takata, S.Hidaka, M.Masuda, T.Ito, Pool Boiling on a Superhydrophilic Surface, International Journal of Energy Research, 10.1002/er.861, 27, 2, 111-119, Vol.27, No.2, pp.111-119, 2003.02.
278. Yasuyuki Takata, S. Hidaka, M. Masuda, T. Ito, Pool boiling on a superhydrophilic surface, International Journal of Energy Research, 10.1002/er.861, 27, 2, 111-119, 2003.02, Titanium Dioxide, TiO2, is a photocatalyst with a unique characteristic. A surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO2-coated and non-coated surfaces were used for comparison. In the case of the TiO2-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface..
279. Sumitomo Hidaka, Yasuyuki Takata, Hiroshi Yamamoto, Akimitsu Yamashita, Takehiro Ito, Wettability and droplet evaporation on plasma-irradiated metal surface, Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.69.437, 69, 678, 437-444, 2003.01, Evaporation of water droplet can be enhanced by plasma irradiation that increases the surface wettability. Relation between plasma irradiation time and contact angle was examined first of three metals and then the lifetime of water drop on hot surface was measured changing the surface wettability by plasma irradiation. The lifetime of water drop decreased and the wetting limit temperature increased with the increasing irradiation time of plasma. Hydrophilicity by plasma irradiation is not a permanent effect but it will be useful for enhancement of cooling of hot metal..
280. Y. Takata, S. Hidaka, J. M. Cao, T. Nakamura, H. Yamamoto, M. Masuda and T. Ito, Effect of Surface Wettability on Boiling and Evaporation, Proceedings of the 3rd International Symposium on Advanced Energy Conversion Systems and Related Technologies(CD-ROM), 10.1016/j.energy.2004.05.004, 30, 2-4, 209-220, Paper No.3B5, 2002.12.
281. Yasuyuki Takata, H. Kubota, T. Ito, Boiling heat transfer to subcooled nitrogen from thin wire in narrow space, 2002 ASME International Mechanical Engineering Congress and Exposition American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD, 10.1115/IMECE2002-39064, 372, 3, 199-204, 2002.12, Boiling heat transfer characteristic of liquid nitrogen was investigated to obtain the basic information on cooling design of high-TC superconducting transformer which is cooled by subcooled nitrogen to avoid bubble formation. Thin wire of platinum-30%/rodium in diameter of 50μm was used as heater and thermometer. The wire was covered outside with acrylic tube to simulate the practical winding condition and we examined the effect of space restriction on boiling heat transfer characteristics. The subcooling of nitrogen tested was between 0 and 10.4K. The results show that the CHF and MHF increase considerably with the degree of subcooling..
282. Y. Takata, H. Kubota and T. Ito, Boiling Heat Transfer to Subcooled Nitrogen from Thin Wire in Narrow Space, Proceedings of 2002 ASME International Mechanical Engineering Congress and Exposition, New Orleans, LA(CD-ROM), IMECE2002-34064, 2002.11.
283. Y. Takata, Photo-induced Hydrophilicity and Its Applications to Phase Change Phenomena, Thermal Science & Engineering, Vol.10, No.6, pp.31-38, 2002.11.
284. Y.Takata, S.Hidaka, H.Yamamoto, M.Masuda, T.Ito, Evaporation of Water Drop on Photo-Induced Hydrophilic Surface, Proceedings of the 12th International Heat Transfer Conference, Vol.3, pp.413-418, 2002.08.
285. Yasuyuki Takata, Sumitomo Hidaka, Hiroshi Yamamoto, Tadamichi Nakamura, Masataka Masuda, Takehiro Ito, Effect of contact angle on droplet evaporation (Control of contact angle by photo-induced hydrophilicity), Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.68.1911, 68, 671, 1911-1918, 2002.07, Titanium Dioxide, TiO2, is one of the photocatalysts that has a very unique characteristic. The surface coated with TiO2 exhibits extremely high affinity for water by exposing the surface to ultraviolet ray and the contact angle decreases nearly to zero. On the contrary, the contact angle increases when the surface is shielded from ultraviolet ray. We have developed two types of TiO2 surface by sputtering process. One is the copper surface with TiO2 layer and the other is with TiO2 and SiO2 layer. The contact angle the former varies between 30-84° and the latter varies between 4-13°. We applied these surfaces to control the contact angles with the other thermal properties of the surface being constant. Experiment of droplet evaporation has been performed to manifest the effect of contact angle on the evaporation curves. It is found that the wetting limit temperature increases as the contact angle decreases to 13°, but it decreases again as the contact angle decreases to 4°..
286. Yasuyuki Takata, Control of Surface Wettability by Plasma Irradiation, Proceedings of the Fourth Pacific Rim Thermal Science and Energy Engineering Workshop (PaRTSEE-4), pp.113-116, 2002.05.
287. Y. Takata, H. Kubota, T. Ito, Boiling heat transfer to subcooled nitrogen from thin wire in narrow space, Heat Transfer, 10.1115/IMECE2002-39064, 199-204, 2002.01, Boiling heat transfer characteristic of liquid nitrogen was investigated to obtain the basic information on cooling design of high-TC superconducting transformer which is cooled by subcooled nitrogen to avoid bubble formation. Thin wire of platinum-30%/rodium in diameter of 50μm was used as heater and thermometer. The wire was covered outside with acrylic tube to simulate the practical winding condition and we examined the effect of space restriction on boiling heat transfer characteristics. The subcooling of nitrogen tested was between 0 and 10.4K. The results show that the CHF and MHF increase considerably with the degree of subcooling..
288. Yasuyuki Takata, Photo-induced hydrophilicity and its applications to boiling and evaporation, Proceedings of the first Taiwan-Japan Workshop on Mechanical and Aerospace Engineering, Tainan, Taiwan, Vol.2, pp.623-634, 2001.12.
289. Yasuyuki Takata, T. Nakamura, M. Masuda, S. Hidaka, H. Yamamoto, T. Ito, Controlled contact angle and droplet evaporation using photo-induced hydrophilic surface, 2001 ASME International Mechanical Engineering Congress and Exposition American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD, 369, 1, 315-321, 2001.12, Titanium Dioxide, TiO2, is one of the photocatalysts that has a very unique characteristic. The surface coated with TiO2 exhibits extremely high affinity for water by exposing the surface to ultraviolet ray and the contact angle decreases nearly to zero. On the contrary, the contact angle increases when the surface is shielded from ultraviolet ray. We have developed two types of TiO2 surface by sputtering process. One is the copper surface with TiO2 layer and the other is with TiO 2 and SiO2 layer. The contact angle of the former varies between 30-82° and the latter varies between 4-13°. We applied these surfaces to control the contact angles with the other thermal properties of the surface being constant. Experiment of droplet evaporation has been performed to manifest the effect of contact angle on the evaporation curves. It is found that the wetting limit temperature increases as the contact angle decreases to 13°, but it decreases again as the contact angle decreases to 4°..
290. Yasuyuki Takata, H. Shirakawa, T. Ito, Y. Haraguch, M. Hariki, Numerical analysis of slit laminar cooling of hot moving slab, First International Conference on Computational Methods in Multiphase Flow, Multiphase Flow I Advances in Fluid Mechanics, 29, 163-172, 2001.12, Numerical analysis has been performed on the slit laminar cooling of a hot moving slab. A hot slab of initial temperature 600°C is cooled by an impinging jet of water and the behavior of the water flow after impingement has been obtained. The numerical method is based on the improved VOF (volume of fluid) method. Flow and temperature fields of the cooling water and the surrounding air and thermal conduction inside the slab are solved simultaneously. The cooling curve and transient heat transfer coefficient are obtained as parameters of the velocity of the slab and the impinging velocity of the cooling water..
291. Y. Takata, S. Hidaka, T. Nakamura, H. Yamamoto, M. Masuda and T. Ito, Controlled Contact Angle and Droplet Evaporation Using Photo-induced Hydrophilic Surface, Proceedings of the 5th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, IMECE2001/HTD-24133, 2001.11.
292. H. Shirakawa, Y. Takata, T. Ito, Volume of fluid method for phase change problems, Thermal Science & Engineering, Vo.9, No.6, pp.29-38, 2001.11.
293. Sanjayan Velautham, Takehiro Ito, Yasuyuki Takata, Zero-emission combined power cycle using LNG cold, JSME International Journal, Series B: Fluids and Thermal Engineering, 10.1299/jsmeb.44.668, 44, 4, 668-674, 2001.11, A potential zero emission combined power generation plant fired by liquefied natural gas (LNG) has been investigated. A mixture of carbon dioxide (CO2)-steam is used as the working fluid of a gas turbine cycle, which replaces the normal combustion-in-air products and air, notably as the thermal ballast for the control of flame temperature. Oxygen (O2) is used as the fuel oxidant and is obtained from an air separation unit (ASU). The excess CO2 due to combustion is extracted by a simple flow separator and liquefied ready to be reused and/or sequestered. The plant configuration and thermodynamics of the cycle are discussed first and then the optimised overall efficiency of the plant is calculated with a comparison of 100% and 120% stoichiometric combustion. The overall net efficiency, optimised to pressure and temperature levels complying with the material and cooling techniques currently available, is around 56% (LHV basis), including the energy penalty of the ASU and the CO2 separation..
294. Sanjayan Velautham, Takehiro Ito, Yasuyuki Takata, Carbon dioxide capture from fossil fuel-fired power generation, Proceedings of the POWER-GEN Asia 2001(CD-ROM), 2001.09.
295. Y. Takata, S. Hidaka, J.M. Cao, T. Nakamura, H. Yamamoto, M. Masuda, T. Ito and T. Watanabe, Boiling and Evaporation Heat Transfer from a TiO2-Coated Surface, Proceedings of the 5th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, Vol.1, pp.203-208, 2001.09.
296. Y. Takata, H. Shirakawa, T. Ito, Volume of fluid method for phase change problems, Proceedings of the Korea-Japan Joint Seminar on Numerical Heat Transfer, pp.9-17, 2001.05.
297. Y.Takata, H.Shirakawa, T.Ito, Y.Haraguchi, M.Hariki, Numerical Analysis of Slit Laminar Cooling of Hot Moving Slab, Proceedings of the First International Conference on Computational Methods in Multiphase Flow, 29, 163-172, pp.163-172, 2001.03.
298. K. Funaki, M. Iwakuma, K. Kajikawa, M. Hara, J. Suehiro, T. Ito, Y. Takata, T. Bohno, S. Nose, M. Konno, Y. Yagi, H. Maruyama, T. Ogata, S. Yoshida, K. Ohashi, H. Kimura, K.Tsutsumi, Development of a 22kV/6.9kV Single-Phase Model for a 3MVA HTS Power Transformer, IEEE Transaction of Applied Superconductivity, 10.1109/77.920079, 11, 1, 1578-1581, Vol.11, No.1, pp.1578-1581, 2001.03.
299. Kazuo Funaki, Masataka Iwakuma, Kazuhiro Kajikawa, Masanori Hara, Junya Suehiro, Takehiro Ito, Yasuyuki Takata, Takaaki Bohno, Shin Ichi Nose, Masayuki Konno, Yujiro Yagi, Hiroshi Maruyama, Takenori Ogata, Shigeru Yoshida, Kouichi Ohashi, Hironobu Kimura, Katsuya Tsutsumi, Development of a 22kV/6.9kV single-phase model for a 3MVA HTS power transformer, 2000 Applied Superconductivity Conference IEEE Transactions on Applied Superconductivity, 10.1109/77.920079, 11, 1 II, 1578-1581, 2001.03, We have developed a 22kV/6.9kV HTS single-phase transformer cooled by liquid nitrogen for field test, which is a practical model for the single-phase part of a 3MVA HTS power transformer. First, we numerically simulated electromagnetic, mechanical and thermal conditions of the windings in accidental cases of short-circuit and lightning impulse, and considered the winding structure withstanding the severe loads. We constructed a small-sized model coil of Bi-2223 Ag/Mn-sheathed tapes and confirmed applicability of the design concept for the over-current and high-withstand-voltage tests. We designed and constructed a single-phase HTS transformer on the basis of the model-coil-test results. The primary and secondary windings are transposed parallel conductors of two and six Bi-2223 Ag/Mn tapes, respectively. The same tests for the HTS transformer as for usual oil-filled ones indicated the reliable operation and high performance. The field test in a distribution grid of Kyushu Electric Power Co. included inrush-current test and long-term operation of the transformer cooled by a continuous supply system of subcooled liquid nitrogen with cryocoolers..
300. T. Ito, Yasuyuki Takata, H. Shirakawa, H. Hamaguchi, A. C.M. Sousa, Numerical simulation of solidification in twin-belt caster, Sixth International Conference on Advanced Computational Methods in Heat Transfer: Heat Transfer 2000 Advanced Computational Methods in Heat Transfer VI, 311-319, 2000.12, A numerical study has been performed to investigate solidification process in a twin-belt caster that is one of the continuous casting process to produce thin slabs. Two parallel moving belts work as endless mold walls and the solidifying shell develops during passing through them. The numerical method is based on improved VOF (Volume of Fluid) method. Two-dimensional flow and temperature fields were obtained with computation parameters of belt speed, heat transfer coefficient between belt and metal, inlet nozzle width, and inlet temperature of metal. The solidification front agrees well with previously reported work..
301. H.Shirakawa, Y.Takata, T.Ito, S.Satonaka, Numerical Solution of Thermal and Fluid Flow with Phase Change by VOF Method, HTD-Vol.366-4, Proceedings of the ASME Heat Transfer Division-2000, Vol.4, pp.247-255, 2000.11.
302. Y.Takata, S.Hidaka, J.M.Cao, K. Tanaka, M.Masuda, T.Ito, T.Watanabe, M.Shimohigoshi, Boiling and Evaporation from a Superhydrophilic Surface, Thermal Science & Engineering, Vol.8, No.6, pp.33-41, 2000.11.
303. Y.Takata, S.Hidaka, J.M.Cao, M.Masuda, T.Ito, T.Watanabe, M.Shimohigoshi, Boiling and Evaporation from a Superhydrophilic Surface, Proceedings of the International Workshop on Current Status and Future Directions in Boiling Heat Transfer and Two-phase Flow, pp.23-29, 2000.10.
304. Y.Takata, S.Hidaka, J.M.Cao, M.Masuda, T.Ito, T.Watanabe, M.Shimohigoshi, Boiling Heat Transfer from a Superhydrophilic Surface, Proceedings of the 3rd European Thermal Sciences Conference, Vol.2, pp.797-801, 2000.09.
305. T.Ito, Y.Takata, H.Shirakawa, M.Hamaguchi, A.C.M.Sousa, Numerical simulation of solidification in twin-belt caster, Advanced Computational Methods in Heat Transfer VI, WIT Press, 3, 311-319, pp.311-319, 2000.06.
306. S. Velautham, T. Ito, Y. Takata, Zero emission gas turbine-steam turbine combined cycle with low-pressure gas turbine exhaust, Memoirs of the Graduate School of Engineering, Kyushu University, 60, 2, 59-75, 2000.06, A potential zero emission power generating combined cycle with a gas turbine(GT) exhaust well below the atmospheric pressure, around 0.1 bar, has been investigated. A mixture of carbon dioxide (CO2)-steam is used as the working fluid of a gas turbine(topper) cycle, which replaces the normal combustion-in-air products, notably as the thermal ballast for the control of flame temperature. Oxygen (O2) from an air separation unit (ASU) is used as the fuel oxidant. The excess CO2 due to combustion is extracted by a simple flow separator and liquefied ready to be reused and/or sequestered. The plant configuration and thermodynamic features are discussed first and then the optimised overall efficiency of the plant is calculated with 100% and 120% stoichiometric O2. Considering all the auxiliary power consumption by air separation and CO2 liquefaction, the overall net efficiency optimised to pressure and temperature levels complying with materials and cooling techniques currently available, is around 57% on a LHV basis, when fuelled by liquefied natural gas (LNG)..
307. Hidemi Shirakawa, Yasuyuki Takata, Torato Kuroki, Takehiro Ito, Improvement of VOF method (2nd report, improved calculation procedures for surface tension term and transport properties), Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.66.647_1667, 66, 647, 1667-1674, 2000.01, Two improvements have been done on VOF (Volume of Fluid) method. First, accuracy of surface tension calculation was improved by selecting surface locations of interface cells. The Second, we developed new method to estimate liquid volume fraction in interface cells that are different from each transport property in staggered mesh system. Comparison between arithmetic and harmonic means has been made both for dielectric constant and viscosity. The result by harmonic mean is closer to exact value than that by arithmetic mean..
308. Hidemi Shirakawa, Yasuyuki Takata, Torato Kuroki, Takehiro Ito, Shinobu Satonaka, Numerical solution of thermal and fluid flow with phase change by VOF method, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.66.649_2405, 66, 649, 2405-2412, 2000.01, Numerical method for thermal and fluid flow with free surface and phase change has been developed. Equations of continuity, Navier-Stokes and energy are solved simultaneously both for liquid and vapor phases. The calculation result of one-dimensional solidification problem agrees with Neumann's theoretical value. In the evaporation of liquid film, the flow caused by volume change with phase change can be calculated. We applied it to a bubble growth in superheated liquid and obtained the result that a bubble grows with spherical shape. The present method can be applicable to various phase change problems..
309. Hidemi Shirakawa, Takehiro Ito, Yasuyuki Takata, Shinobu Satonaka, Numerical solution of thermal and fluid flow with phase change by vof method, Unknown Journal, 366, 247-255, 2000, Numerical method for thermal and fluid flow with free surface and phase change has been developed. The calculation result of one-dimensional solidification problem agrees with Neumann's theoretical value. We applied it to a bubble growth in superheated liquid and obtained the result that a bubble grows with spherical shape. The present method can be applicable to various phase change problems..
310. Y.Takata, K.Tanaka, K.Kaijima, T.Ito, T.Watanabe, M.Shimohigoshi, Enhancement of Boiling and Evaporation Heat Transfer by Superhydrophilic Photocatalyst, Proceedings of the 6th UK National Conference on Heat Transfer, Edinburgh, 1999, 7, 323-328, pp.323-328, 1999.09.
311. Y.Takata, K.Tanaka, K.Kaijima, T.Ito, T.Watanabe, M.Shimohigoshi, Enhancement of Heat Transfer with Liquid-Vapor Phase Change by Photo-Induced Hydrophilicity, Proceedings of the 33rd National Heat Transfer Conference(CD-ROM), Paper No. NHTC99-080, 1999.08.
312. S.Velautham, T.Ito, Y.Takata, H.Mori, LNG Fired Zero Emission Combined Power Plant, Proceedings of the Fifth International Conference on Technologies and Combustion for a Clean Environment, Vo.1, pp.399-404, 1999.07.
313. Sanjayan Velautham, Takehiro Ito, Yasuyuki Takata, Hideo Mori, LNG fired zero emission combined power generation plant, Memoirs of the Graduate School of Engineering, Kyushu University, 59, 2, 125-136, 1999.06, The potential of a zero emission combined power generation plant fired by liquefied natural gas (LNG) has been investigated. The thermodynamic cycle proposed is basically an integration of a combined cycle power generation plant, an air separation unit (ASU), and a carbon dioxide (CO2) recovery unit, while the by-products are liquefied CO2, gaseous nitrogen (N2) and water (H2O). LNG is burnt in oxygen (O2)-CO2 mixture and recirculated in a gas turbine-steam turbine combined power generation plant. Such recirculation leads to flue gas with very high CO2 concentration. O2 for combustion is obtained from ASU. LNG is used in both cooling the air for the ASU and to condense a part of the flue gas. By integrating the ASU and the combined power generation plant, the overall thermal efficiency calculated is around 47% (LHV)..
314. Y.Takata, H.Shirakawa, T.Kuroki, T.Ito, An Improved VOF Method and Its Applications to Phase Change Problems, Proceedings of the 5th ASME/JSME Thermal Engineering Joint Conference, Paper No.AJTE99-6424, 1999.03.
315. Y.Takata, H.Shirakawa, H.Sasaki, T.Kuroki, T.Ito, Numerical Analysis of Rapid Solidification in a Single Roller Process, Heat Transfer-Asian Research, Vol.28, No.1, pp.34-49, 1999.01.
316. Yasuyuki Takata, H. Shirakawa, H. Sasaki, T. Kuroki, T. Ito, Numerical analysis of rapid solidification in a single roller process, Heat Transfer - Asian Research, 28, 1, 34-49, 1999.01, The rapid solidification in a single roller process has been used to make amorphous ribbons. Because this process occurs rapidly, it is difficult to obtain useful experimental data. Therefore, a numerical analysis has been performed on the rapid solidification in a single roller cooling process. The VOF (volume of fluid) method was adopted as the numerical method used to simulate transient two-dimensional thermal and fluid flow with a liquid-solid phase change and free surfaces. We simulated the behavior of an aluminum alloy. The geometry of the amorphous ribbon, flow and temperature fields, temperature history of alloy particle whose initial location is at the center of the nozzle, and the cooling rate were obtained using as parameters the roll velocity, the nozzle slot breadth, and the gap between nozzle and roller..
317. Y.Takata, H.Shirakawa, T.Kuroki, T.Ito, Numerical Analysis of Single Bubble Departure from a Heated Surface, Proceedings of the 11th International Heat Transfer Conference, 355-360, Vol.4, pp.355-360, 1998.08.
318. T.Ito, R.Akasaka, W.L.Cheng, T.Iwamoto, Y.Kato, T.Kuroki, T.Shigechi, Y.Takata, H.Tanigawa, T.Hamatake, T.Fujita, T.Honda, T.Masuoka, M.Miyamoto, S.Momoki, T.Yamaguchi, H.Yamashita, K.Yoshioka, PROPATH Ver.10.2: A Program Package for Thermophysical Properties of Fluids, Proceedings of the 5th Asian Thermophysical Properties Conference, pp.257-260, 1998.08.
319. Y, Takata, H.Shirakawa, H.Sasaki, T.Kuroki, T.Ito, Numerical Simulation of Solidification Process in Casting of Amorphous Ribbon, 3rd International Thermal Energy Congress, Kitakyushu, pp.215-220, 1997.07.
320. T.Ito, Y.Takata, H.Shirakawa, Y.Kawagoe, T.Okashiro, T.Aoki, Thermal Interaction between Molten Metal and Water, Proceedings of the International Seminar on Vapor Explosions and Explosive Eruptions, pp.111-116, 1997.05.
321. Y. Takata, H. Shirakawa, H. Sasaki, T. Kuroki, T. Ito, Numerical analysis of rapid solidification in a single roller process, Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.63.611_2413, 63, 611, 2413-2420, 1997.01, The rapid solidification in a single roller process has been used to produce an amorphous ribbon. The thermal and fluid flow in that process is accompanied by free surfaces and a phase change. Since the cooling process is carried out over a very short time period, it is difficult to measure transient temperature distribution or cooling rates directly from the experiment. The present paper proposes a numerical method which is capable of simultaneously solving the thermal and fluid flow in molten metal and surrounding air and transient heat conduction in a cooling roller. The method, based on the VOF (Volume of Fluid) method, is improved to enable simulation of a transient two-dimensional thermal and fluid flow with a liquid-solid phase change and free surface. We simulated the cooling process of aluminum alloy amorphous ribbon. The shape of the amorphous ribbon, flow, temperature field and cooling rate were numerically obtained using parameters of the roll velocity, the nozzle slot breadth and the gap between nozzle and roller..
322. Hidemi Shirakawa, Yasuyuki Takata, Torato Kuroki, Takehiro Ito, Improvement of donor-acceptor method and the calculation of surface tension force term in VOF (volume of fluid) method, Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.62.4068, 62, 604, 4068-4075, 1996.01, A new donor-acceptor method and a calculation technique for estimating the surface tension force term have been developed in order to improve VOF (volume of fluid) method. The improved VOF consists of (1) calculation of liquid quantity transferred from donor to acceptor cell by grouped into 11 interface patterns, (2) correction of liquid transfer rate by considering movement in oblique direction, (3) correction of inner cells with defects under conservation of total liquid quantity, (4) highly accurate calculation technique for estimating the surface tension force term by approximating the liquid-vapor interface to a circle. We applied the improved VOF method to a simulation of oscillating liquid drop in which the surface tension force is dominant and the obtained frequency agrees well with the theoretical one..
323. Yasuyuki Takata, Hidemi Shirakawa, Katsunori Tanaka, Torato Kuroki, Takehiro Ito, Numerical analysis of bubble growth under electric field, Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.62.1142, 62, 595, 1142-1147, 1996.01, Numerical analysis has been performed on bubble growth and deformation under an electric field in order to elucidate the mechanisms of boiling heat transfer enhancement by EHD (Electro-Hydrodynamic) effects. Transient Navier-Stokes and Maxwell's equations were solved simultaneously for liquid and vapor phases in a two-dimensional cylindrical co-ordinate system making use of the VOF (Volume of Fluid) method. Bubble growth in liquid R113 under atmospheric pressure has been simulated. First, elongation of a single bubble under uniform electric field is simulated and the final shapes of the bubble are found to be in good agreement with Garton's analytical and experimental results. Second, the bubble deformation process under non-uniform electric field was simulated. A bubble initially attached to the lower electrode starts to deform and finally detaches from the lower electrode. The shape of bubble depends on the intensity of the electric field. The behavior of bubbles, the velocity vectors, and the contours of electric field are also shown and compared with experiment..
324. Y.Takata, H.Shirakawa, K.Tanaka, T.Kuroki, T.Ito, Numerical Analysis of a Bubble Growth under the Electric Field, Numerical Methods in Thermal Problems, Vol.9, No.2, pp.1195-1206, 1995.07.
325. T.Ito, Y.Takata, M.M.M.Mousa, Studies on the Water Cooling of Hot Surfaces (Analysis of Spray Cooling in the Region Associated with Film Boiling), JSME International Journal, Series II, 35, 4, 589-598, Vol.35, No.4, pp.589-598, 1992.11.
326. T.Ito, Y.Takata, D.Kasao, Stability Analysis of Forced-Flow Cooled Superconductor, Cryogenics, Vol.32, No.5, pp.439-444, 1992.05.
327. Takehiro Ito, Yasuyuki Takata, Mousa M.M. Mousa, Studies on the water cooling of hot surfaces. (Analysis of spray cooling in the region associated with film boiling), JSME International Journal, Series 2: Fluids Engineering, Heat Transfer, Power, Combustion, Thermophysical Properties, 10.1299/jsmeb1988.35.4_589, 35, 4, 589-598, 1992.01, An analytical study has been performed on the spray cooling of a hot surface in the region associated with film boiling under the assumption that there will be two parallel conductances of heat transfer. One is of radiation from the hot surface to the environment, the correlation of which is cited from the authors' preceding report. The other is heat transfer to the sprayed water droplets by heat conduction through the hypothetical uniform vapor layer underneath the droplet which is in the spheroidal state with a flat bottom. First, we deduce analytically an expression for heat transfer per droplet by solving the equations of momentum in the vapor layer, energy balance at the interface and balance of static forces exerting on a droplet simultaneously. Then a semiempirical correlation of the mean lifetime of the droplets is estimated using the experimental data with surface superheating below 500 K at atmospheric environmental pressure, mass velocity of water between 0.0162 and 0.174 kg/(m2·s), volume mean diameter of droplets between 130 and 550 μm and Weber number between 10 and 120. The procedure we propose predicts the heat transfer data of spray cooling within the experimental range mentioned above fairly well..
328. T. Ito, Y. Takata, D. Kasao, Stability analysis of a forced-flow cooled superconductor, Cryogenics, 10.1016/0011-2275(92)90072-I, 32, 5, 439-444, 1992, A numerical analysis of the thermal stability of a superconductor composite cooled by forced-flow supercritical helium has been performed. The analytical model consists of simultaneous two-dimensional coolant flow equations and a one-dimensional superconductor equation. The equations of conservation of mass, momentum and energy for coolant flow and the Fourier heat conduction equation for the superconductor were solved numerically. Current-sharing mode, temperature-dependent properties of the conductor, and pressure- and temperature-dependent coolant properties were fully taken into account. The transient behaviour of the conductor, coolant flow, the effects of disturbance-heated length of the conductor, the initial pressure and initial velocity of coolant on the thermal stability of superconductors are discussed..
329. M.M.M.Mousa, T.Ito, Y.Takata, Studies on the Spray Cooling of Hot Surfaces, Proceedings of the Al-Azhar Engineering Second International Conference, Egypt, (Dec., 1991), Vol.7, pp.119-133, 1991.12.
330. T.Ito, Y.Takata, D.Kasao, Stability Analysis of Forced-Flow Cooled Superconductor, Japan-U.S. Seminar on Basic Mechanism of Helium Heat Transfer and Related Influence on Stability of Superconducting Magnets II, Los Angeles, (Aug., 1991), 1991.08.
331. Takehiro Ito, Yasuyuki Takata, Mousa M M Mousa, Hiroto Yoshikai, Studies on the water cooling of hot surfaces (experiment of spray cooling), Memoirs of the Faculty of Engineering, Kyushu University, 51, 2, 119-144, 1991.06, An experimental study has been performed on the spray cooling of hot surfaces in the range of mass velocity of water of 0.0162 approximately 0.1737 [kg/(m2·s)] with four different full cone nozzles. Heat transfer characteristics below surface superheating of 500 [K] were investigated, and the effect of subcooling of sprayed water on the heat flux was also examined. An experimental correlation for the heat transfer effectiveness η = qw/[W(CplΔTsub + L + CpvΔTsat)] in the region associated with film boiling was obtained..
332. T.Ito, Y.Takata, D.Kasao, M.Kobayashi, M.Ueda, Stability Analysis of Forced-Flow Cooled Superconductor, Proceedings of the 9th International Heat Transfer Conference, Jerusalem (Aug., 1990), Vol.2, pp.325-330, 1990.08.
333. T.Ito, Y.Takata, Z.H.Liu, H.Nakashima, On the Water Cooling of Hot Surfaces -Analysis of Fog Cooling in the Region Associated with Film Boiling-, Proceedings of the ICHMT International Symposium on Manufacturing and Materials Processing, Dubronik (Aug., 1990), Vo.1, pp.553-567, 1990.08.
334. T.Ito, Y.Takata, H.Kubota, T.Uehara, A.Makino, Pool Boiling Heat Transfer from Porous Surface to Liquid Nitrogen, Proceedings of the 13th International Cryogenic Engineering Conference, 30, 292-296, pp.292-296, 1990.04.
335. T.Ito, Y.Kato, T.Kuroki, T.Shigechi, Y.Takata, H.Tanigawa, T.Honda, T.Masuoka, M.Miyamoto, Y.Yasuda, H.Yamashita, K.Yoshioka, A Function Type Computer Program Package for Thermophysical Properties, Properties of Water and Steam: Proceedings of the 11th International Conference on Properties of Steam Sept. 4-8, 1989, Prague, Chechoslovakia, pp.69-76, 1989.09.
336. Takehiro Ito, Yasuyuki Takata, Zhen hua Liu, On the Water Cooling of Hot Surfaces
(Analysis of Fog Cooling in the Region Equivalent to Film Boiling), Transactions of the Japan Society of Mechanical Engineers Series B, 10.1299/kikaib.55.805, 55, 511, 805-813, 1989.01, A theoretical study has been conducted on air-atomized fog cooling in the region equivalent to film boiling with low mass velocity of water. In the analysis, total heat flux is expressed by the sum of three components, i.e. radiation, forced convection by air flow and evaporation of liquid droplets. The air flow is approximated by an axisymmetric laminar stagnation flow. It is assumed that spherical droplets float on the vapor film formed along the hot surface and move in the radial direction with a droplet is estimated by conduction through the vapor film. It has been derived that heat flux by evaporation increases linearly with the mass velocity of water and inversely with the square root of diameter and impinging velocity of the droplet. The prediction performance of the proposed analysis if fairly good..
337. Takehiro Ito, Yasuyuki Takata, Zhen Hua Liu, Hajime Nakashima, Shiraishi Norihisa, Studies on the water cooling of hot surfaces (experiment of fog cooling), Memoirs of the Faculty of Engineering, Kyushu University, 48, 3, 211-229, 1988.09, Experimental studies have been performed on the fog cooling of hot surfaces in the range of relatively low mass velocity of water. Flow characteristics of an air-atomized fog nozzle such as the radial distribution of mass velocity of water, the impact velocity and the diameter of water droplets were measured precisely. Heat transfer characteristics in the range of the surface temperature below 500°C were investigated..
338. T.Ito, Y.Takata, H.Kubota, T.Honnami, Measurement of Thermophysical Properties at Low Temperature by Rectangular-Shaped Pulse Heating, Proceedings of the Twelfth International Cryogenic Engineering Conference, Southermpton (Jul. 1988), pp.409-413, 1988.07.
339. Takehiro Ito, Yasuyuki Takata, Hiromi Kubota, Tetsuji Honnami, Measurement of thermophysical properties at low temperatures by rectangular-shaped pulse heating, Transactions of the Japan Society of Mechanical Engineers Series B, 10.1299/kikaib.54.2556, 54, 505, 2556-2559, 1988.01, A transient method with pulse heating has been developed to determine the specific heat and thermal conductivity of Bakelite (phenol-formaldehyde resin) in the temperature range of 4.44-9.15K. The temperature excursion in an infinite cylinder with an insulated outer surface and with a cylindrical heat source embedded in it was calculated initially. In the calculation, the heat source released heat as a rectangular-shaped pulse in the time direction. The ratio of the temperature rise at any two time instances was found to be a function only of the Fourier numbers associated to those instances. Therefore, by measuring that ratio, thermal diffusivity was determined while the specific heat could be calculated by the ultimate temperature rise. It was recognized in the temperature range tested that the specific heat and thermal conductivity increased with temperature while the thermal diffusivity decreased with it. The temperature dependence of the specific heat measured is similar to that for Formite Bakelite varnish in the literature..
340. U.Ruppert, W.Z.Yang, K.Lueders, K.Funaki, Y.Takata, M.Takeo, F.Irie, Heat Transfer Investigations of Superconductors in Pressurized He II, Proceedings of the 18th International Conference on Low Temperature Physics, Kyoto, 1987, 26, 1537-1538, Vo.26, pp.1537-1538, 1987.08.
341. Udo Ruppert, W. Z. Yang, Klaus Lüders, K. Funaki, Y. Takata, M. Takeo, F. Funaki, Heat Transfer Investigations of Superconductors in Pressurized He II, Japanese journal of applied physics, 10.7567/JJAPS.26S3.1537, 26, S3-2, 1537-1538, 1987.01, Measurements of steady state and transient heat transfer on bare superconducting NbTi-wires in pressurized super fluid helium were performed. Results of the extreme thermal stability of the cooling, which explains the vanishing propagation velocity under these conditions, are reported..
342. K. Funaki, Yasuyuki Takata, M. Takeo, F. Irie, U. Ruppert, W. Z. Yang, E. Kristen, K. Lueders, G. Klipping, EFFECTS OF AN INSULATION LAYER ON THE PROPAGATION OF A NORMAL ZONE IN SUPERCONDUCTING WIRES BELOW 4. 2 K., Proceedings of the International Cryogenic Engineering Conference, 730-734, 1986.12, The propagation velocity of a normal zone in NbTi multi-filamentary superconducting wires has been measured in the bath temperature range of 2. 05-4. 2 K. Bare and insulated wires were utilized for the experiment in order to examine the effect of an insulation layer. For the bare wire the propagation velocity decreases gradually with decreasing temperature, then drastic reduction was observed near the lambda point, and finally no propagation occurs in pressurized He II. For the insulated wire, on the other hand, the velocity is three times larger than that for the bare wire at 4. 2 K and the propagation was observed even in He II. Numerical analysis was performed for the insulated wire. The results agree quantitatively with the experiments..
343. T. Ito, Yasuyuki Takata, D. Kasao, M. Yamaguchi, T. Hara, FORCED-CONVECTION HEAT TRANSFER TO SUPERCRITICAL HELIUM FLOWING IN A VERTICAL STRAIGHT CIRCULAR TUBE., AIChE Symposium Series, 86-91, 1986.12, Forced-convection heat transfer to supercritical helium has been investigated. The test section is a 1. 25 left bracket mm right bracket inner diameter and 200 left bracket mm right bracket long straight tube through which helium flows upward or downward, heated uniformly. The conditions covered are inlet fluid temperature between 4. 7 and 10. 8 left bracket K right bracket , system pressures of 0. 3, 0. 5 and 0. 8 left bracket MPa right bracket , mass velocities of 20, 40 and 80 left bracket kg/(m**2 multiplied by (times) S) right bracket and heat fluxes of 500, 1000, 2000 and 4000 left bracket W/m**2 right bracket . Experimental results on the distributions of wall temperature and heat transfer coefficient are presented and a comparison of experimental results between those for upward and downward flow directions and discussion about the differences between them are done in the light of the effect of buoyancy..
344. T.Ito, Y.Takata, D.Kasao, M.Yamaguchi, T.Hara, Forced-Convection Heat Transfer to Supercritical Helium Flowing in a Vertical Straight Circular Tube, Cryogenic Properties, Process and Applications -1986, AIChE Symposium Series, Vol.82, No.251, pp.86-91, 1986.11.
345. T.Ito, Y.Takata, H.Kubota, M.Uesono, Transient Pool Boiling Heat Transfer to Helium 4 from Flat Surfaces - 2nd Report, Proceedings of the 11th International Cryogenic Engineering Conference, West Berlin (Apr. 1986), pp.638-643, 1986.04.
346. K.Funaki, Y.Takata, M.Takeo, F.Irie, U.Ruppert, W.Z.Yang, E.Kirsten, K.Lueders, G.Klipping, Effects of an Insulation Layer on the Propagation of a Normal Zone in Superconducting Wires below 4.2 K, Proceedings of the 11th International Cryogenic Engineering Conference, West Berlin (Apr. 1986), pp.730-734, 1986.04.
347. Takehiro Ito, Yasuyuki Takata, Hiromi Kubota, Masahiro Uesono, TRANSIENT POOL BOILING HEAT TRANSFER TO HELIUM 4 FROM FLAT SURFACES - 2ND REPORT., Proceedings of the International Cryogenic Engineering Conference, 638-643, 1986, Experiments on transient pool boiling heat transfer to liquid helium 4 for the step type heat flux,q,application have been carried out at the atmospheric pressure. Thin carbon films worked as heater and as thermometer at the same time. Two types of test piece were made. Substrate of the first type had carbon film on one side of it and that of the second type was sandwiched between two layers of carbon film to reduce the heat loss. The temperature excursions were measured in the heat flux range from 1. 9 to 100 left bracket kW/m**2 right bracket . The results have indicated that the Kapitza conductance h k,ref at the reference temperature Tk,ref ( equals 4. 2 left bracket K right bracket in this report) is around 30 left bracket kW/m**2 multiplied by (times) K right bracket and the time at the onset of transition to film boiling tf obeys a q** minus **2 relationship..
348. Y.F.Rao, Y.Miki, K.Fukuda, Y.Takata, S.Hasegawa, Flow Patterns of Natural Convection in Horizontal Cylindrical Annuli, International Journal of Heat and Mass Transfer, 28, 3, 705-714, Vol.28, No.3, pp.705-714, 1985.03.
349. Rao Yan-Fei, Miki Yasutomi, Fukuda Kenji, Yasuyuki Takata, Hasegawa Shu, Flow patterns of natural convection in horizontal cylindrical annuli, International Journal of Heat and Mass Transfer, 10.1016/0017-9310(85)90193-0, 28, 3, 705-714, 1985.01.
350. T.Ito, K.Matsumoto, H.Yamashita, T.Shigechi, Y.Takata, T.Kuroki, A Function Type Computer Program Package for Thermophysical Properties, Proceedings of the 10th International Conference on the Properties of Steam, Moscow (ICPS), Vol.1, pp.273-283, 1984.09.
351. Y.Takata, K.Iwashige, K.Fukuda, S.Hasegawa, Three-Dimensional Natural Convection in an Inclined Cylindrical Annulus, International Journal of Heat and Mass Transfer, Vol. 27, No. 5, pp.747-754, 1984.05.
352. Takata Yasuyuki, Iwashige Kengo, Fukuda Kenji, Hasegawa Shu, Three-dimensional natural convection in an inclined cylindrical annulus, International Journal of Heat and Mass Transfer, 10.1016/0017-9310(84)90144-3, 27, 5, 747-754, 1984.05, An analytical and experimental work is described on natural convection in an inclined cylindrical annulus enclosed in heated inner and cooled outer cylinders. Three-dimensional governing equations are transformed into the finite-difference equations and solved numerically using the successive over-relaxation (SOR) procedure. The three-dimensional structure of the fluid flow and temperature distributions as well as Nusselt numbers are obtained and the effect of inclination on them is examined. A flow visualization experiment using a tracer technique is conducted; photographs of streaklines confirm the three-dimensional flow structure obtained analytically..
353. Yasuyuki Takata, Kenji Fukuda, Shu Hasegawa, Experimental Study on Natural Convective Heat Transfer in a Porous Medium Enclosed in an Inclined Cylindrical Annulus, Transactions of the Japan Society of Mechanical Engineers Series B, 10.1299/kikaib.50.832, 50, 451, 832-838, 1984.01, An experimental study has been conducted on natural convective heat transfer characteristics in a porous medium confined in an inclined cylindrical annulus heated from inside and cooled from outside. Effects of inclination and RaDa on temperature distribution and average Nusselt number are examined. The experimental results are compared with the previously obtained three-dimensional numerical one and a good agreement between them is obtained. Thermal oscillations with long periods are observed at the upper part of the annulus in the case with small inclination and large RaDa..
354. Y.Takata, K.Fukuda, S.Hasegawa, K.Iwashige, H.Shimomura, K.Sanokawa, Three-Dimensional Natural Convection in a Porous Medium in a Vertical Curved Annulus, Numerical Heat Transfer, Vol. 6, No.1, pp.29-39, 1983.01.
355. Yasuyuki Takata, Kenji Fukuda, Shu Hasegawa, Kengo Iwashige, Hiroaki Shimomura, Konomo Sanokawa, Three-dimensional natural convection in a porous medium enclosed in a vertical curved annulus, Numerical Heat Transfer, 10.1080/01495728308963072, 6, 1, 29-39, 1983.01, A numerical analysis has been performed on the three-dimensional natural convecrive heat transfer characteristics of a porous medium enclosed by a vertical concentric curved annulus heated from the inner surface and cooled from the outer surface with relation to the thermal insulation layer in the high-temperature ducting system of a high-temperature gas-cooled reactor. Darcy’s law and the Boussinesq approximation are assumed to be applicable. The governing equations are transformed into finite-difference equations, which are numerically solved by a successive over-relaxation procedure for a range of RaDa (a product of the Rayleigh number and the Darcy number) from 100 to 800. Two typical vertical arrangements (case A, in which a 90° bend is attached at the upper part of a vertical straight tube, and case B, in which it is attached at the lower part) were analyzed and compared with each other. The numerical results show that the flow field and the temperature profile have characteristics of those for both horizontal and vertical annuli, and the insulation performance in case B becomes worse than in case A for a whole range of RaDa. Information useful for the thermal insulation design of a high-temperature ducting system was obtained..
356. Y.Takata, K.Fukuda, S.Hasegawa, K.Iwashige, H.Shimomura, K.Sanokawa, Three-Dimensional Natural Convection in a Porous Medium Enclosed with Concentric Inclined Cylinders, Proceedings of the 7th International Heat Transfer Conference, Munich, Vol.2, pp.351-356, 1982.09.
357. Yasuyuki Takata, Kenji Fukuda, Shu Hasegawa, Kengo Iwashige, Hiroaki Shimomura, Konomo Sanokawa, Heat Transfer Characteristics of Vertical Curved Annular Insulation Layer Numerical Analysis of Three-Dimensional Natural Convection in Porous Medium, (2), Journal of the Atomic Energy Society of Japan / Atomic Energy Society of Japan, 10.3327/jaesj.24.561, 24, 7, 561-566, 1982.01, Numerical analysis has been performed on three-dimensional natural convective heat transfer characteristics in a porous medium enclosed with a vertical concentric curved annulus with relation to the thermal insulation layer in the high temperature ducting system of HTGR. The Darcy's law and the Boussinesq's approximation are assumed to be applicable. Governing equations are transformed into the finite difference equations which are numerically solved by means of successive over-relaxation procedure for a range of RaDa (a product of Rayleigh number Ra and Darcy number Da) from 100 to 800. Two typical cases of vertical arrangement A and B were analyzed and compared each other. Results show that the flow field and the temperature profile have both characteristics of those for horizontal and vertical annulli, and the insulation performance in Case B becomes worse compared with Case A for all over the range of RaDa. Available informations were obtained with respect to the thermal insulation design of high temperature ducting system..
358. Yasuyuki Takata, Kenji Fukuda, Shu Hasegawa, Kengo Iwashige, Hiroaki Shimomura, Konomo Sanokawa, THREE-DIMENSIONAL NATURAL CONVECTION IN A POROUS MEDIUM ENCLOSED WITH CONCENTRIC INCLINED CYLINDERS., Heat Transfer, Proceedings of the International Heat Transfer Conference, 351-356, 1982.
359. Yasuyuki Takata, Kenji Fukuda, Shu Hasegawa, Hiroaki Shimomura, Konomo Sanokawa, Heat Transfer Characteristics of Inclined Annular Insulation Layer, Nippon Genshiryoku Gakkaishi/Journal of the Atomic Energy Society of Japan, 10.3327/jaesj.23.66, 23, 1, 66-75, 1981.01, Numerical analysis has been performed on three-dimensional natural convection in thermal insulation layer enclosed with concentric inclined cylinders. Darcy’ law and Boussinesq, approximation are assumed to be applicable. Governing equations are numerically solved by means of successive over-relaxation methods for ranges of RaDa (a product of Rayleigh number Ra and Darcy number Da) from 1 to 1,000 and δ (an angle of inclination of cylinders from the horizon) from 0 to Π/2. Results show that the fluid particle path draws the co-axial double spiral and that the local Nusselt number Nu1 on the inner cylinder wall has its maximum value at Φ=0 and ξ=0 (bottom end), while Nu2 on the outer cylinder wall has its maximum at ξ=ξmax (top end) and Φ with some deviation from Π. However, the average Nusselt number depends largely on only RaDa and is hardly affected by the inclination..
360. K.Fukuda, Y.Takata, S.Hasegawa, H.Shimomura, K.Sanokawa, Three-dimensional Natural Convection in a Porous Medium between Concentric Inclined Cylinders, Proceedings of the 19th National Heat Transfer Conference, Orlando ASME, HTD-Vol.8, HTD-Vol.8, pp.97-103, 1980.08.
361. K. Fukuda, Y. Takata, S. Hasegawa, H. Shimomura, K. Sanokawa, THREE-DIMENSIONAL NATURAL CONVECTION IN A POROUS MEDIUM BETWEEN CONCENTRIC INCLINED CYLINDERS., Nat Convection in Enclosures, presented at Natl Heat Transfer Conf, 19th American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD, 8, 97-103, 1980.01, Numerical analysis has been performed on three-dimensional natural convection enclosed with concentric inclined cylinders. Darcy's law and Boussinesq's approximation are assumed to be applicable. Governing equations are numerically solved by means of successive over-relaxation method..