Language：English  

Language：Japanese  

Language：English  

Language：English  

Language：Japanese  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Publisher：Journal of Physics: Conference Series  

Spray cooling is a crucial process of steel manufacturing, nuclear power plants and electronics thermal management. However, its precise control is challenging due to the various boiling regimes involved at different temperature levels. Transition from film boiling to nucleate boiling, namely, the onset of quench is our particular interest as it remarks the thermal history of the hot object. Based on our previous findings that quench occurs at a specific temperature defined at the droplet-surface interface we demonstrate that micropillars on steel plates can increase the quench temperature Tq . We performed water spray cooling tests with stainless-steel samples, on which various configurations of micropillars were fabricated using laser texturing. Interestingly, we observed two stages of quench for a specific sample: a drastic increase in the cooling rate at ca. 450 °C, followed by another increase at ca. 250 °C. The first cooling rate increase is attributed to the initiation of stable liquid-solid contact at the pillar tops. Eventually, water wets the entire pillars and the bottom surface, further increasing the cooling rate. Samples with higher pillars showed no film boiling regime in the experiment, implying higher quenching temperature (Tq > 600 °C). We attribute the increased apparent Tq to the narrow heat conduction path within the micropillar, resulting in a significant temperature drop at the tip which enhances liquid-solid contact.

DOI： 10.1088/1742-6596/2766/1/012141

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Record low thermal conductivity was achieved in large-scale crystal silicon due to the effect of inhomogeneous internal strain-induced phonon engineering via HPT processing.

DOI： 10.1039/d3ta03011c

Scopus

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Language：Japanese   Publisher：日本伝熱学会  

CiNii Research

Language：Japanese   Publisher：Japan Association of Aerosol Science and Technology  

DOI： 10.11203/jar.37.261

Scopus

CiNii Research

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Applied Physics  

We report on electric, thermal, and optical properties of Si subjected to severe plastic deformation. Single-crystalline Si wafers were processed by high-pressure torsion (HPT) under a nominal pressure of 6 GPa. The HPT-processed samples consisted of metastable body-centered-cubic Si-III and rhombohedral Si-XII as well as diamond-cubic Si-I and amorphous phases. The metastable phases increased with increasing the number of anvil rotations (N). The resistivity of the single-crystalline Si (20 ω cm) increased to 50 ω cm after HPT processing for N = 10 and then it decreased to ∼0.7 ω cm when increasing N to 100. Such an increase and a subsequent decrease in resistivity were attributed to the grain refinement and the increase in the volume fraction of semimetallic Si-III, respectively. The thermal conductivity was reduced by two orders of magnitude (∼3 W m-1 K-1) after HPT processing for N ≥ 50. A weak broad photoluminescence peak originating from Si-I nanograins appeared in the visible light region after annealing at 600 °C. These results indicate that the resistivity, thermal conductivity, and photoluminescence of the HPT-processed Si strongly depend on the formation of metastable phases and grain refinement, which are induced by shear strain under high pressure.

DOI： 10.1063/5.0122826

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The present contribution addresses an open question about spray cooling: when does quenching occur? We performed water spray cooling tests with heated iron disks at system pressures ranging from 0.1 MPa to 0.5 MPa. Sample heating was carried out under high vacuum and then spray cooling in an argon environment, minimising the effect of surface oxidisation. The temperature for the onset of quenching was found to increase with the system pressure. We demonstrated that the quenching point could be predicted reasonably well by a mechanistic model that considers the force balance at the interface between the droplet and the vapour film underneath it. The influence of droplet impact velocity was also discussed. From the temperature histories obtained by the cooling tests, the rate of heat transfer in the film boiling regime was evaluated and found to increase with the system pressure. This was due to the increase in the saturation temperature which then led to the reduction of vapour film thickness, as corroborated by a Leidenfrost droplet model. Using the spray parameters, we quantified the amount of heat removed by a single droplet and compared it with theoretical models. Our analysis suggested a potential existence of partial droplet-surface contact even in the film boiling regime.(c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

DOI： 10.1016/j.ijheatmasstransfer.2022.122795

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Bulletin of the Chemical Society of Japan  

Current greenhouse gas emissions suggest that keeping global temperature increase below 1.5 degrees, as espoused in the Paris Agreements will be challenging, and to do so, the achievement of carbon neutrality is of utmost importance. It is also clear that no single solution can meet the carbon neutral challenge, so it is essential for scientific research to cover a broad range of technologies and initiatives which will enable the realization of a carbon free energy system. This study details the broad, yet targeted research themes being pioneered within the International Institute for Carbon-Neutral Energy Research (I2CNER). These approaches include hydrogen materials, bio-mimetic catalysts, electrochemistry, thermal energy and absorption, carbon capture, storage and management and refrigerants. Here we outline the state of the art for this suite of technologies and detail how their deployment, alongside prudent energy policy implementation can engender a carbon neutral Japan by 2050. Recognizing that just as no single technological solution will engender carbon neutrality, no single nation can expect to achieve this goal alone. This study represents a recognition of conducive international policy agendas and is representative of interdisciplinary, international collaboration.

DOI： 10.1246/bcsj.20210323

Web of Science

Scopus

Language：Japanese   Publisher：National Committee for IUTAM  

<p>The present work attempts to elucidate the mechanism of quenching processes during spray cooling. Water spray cooling tests were conducted with heated iron disks at system pressures of 0.1 MPa–0.5 MPa. Extra care was taken to minimize the effect of surface oxidization. We demonstrated that the quenching temperature can be predicted using a mechanistic model, considering the forces acting at the interface between the droplet and the vapor film underneath it. We also modelled heat transfer from the surface to the droplet, extended it to the spray level, and simulated thermal histories until the onset of quenching.</p>

DOI： 10.11345/japannctam.66.0_111

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

A dynamics study of surface nanobubbles using liquid phase electron microscopy showcases their unique push–push behavior.

DOI： 10.1039/d1cp03451k

Language：English   Publishing type：Research paper (scientific journal)  

We present a combined experimental and numerical investigation of phonon transport in multiphase nanostructured silicon. The sample was synthesized by high-pressure torsion with a nominal pressure of 24GPa. Based on the x-ray diffraction measurement, we have identified the existence of three phases of silicon in the sample: Si-I, Si-III, and Si-XII, with volume fractions of 66&#37;, 25&#37;, and 9&#37; and average grain sizes of 25, 14, and 11nm, respectively. The measured thermal conductivities of the sample in the temperature range of 150-330K are on the order of 5W/(mK) and exhibit weak temperature dependence. A multiscale modeling that incorporates first-principles lattice dynamics, the Monte Carlo ray-tracing method, and effective medium theory was used to understand the mechanism of phonon transport in multiphase nanostructured silicon as well as the weak temperature dependence. We found that the thermal conductivity of single-phase nanostructured silicon decreases with decreasing average grain size and is about an order of magnitude lower than the corresponding bulk counterpart when the average grain size isO (10The weak temperature-dependent thermal conductivity in the nanostructured silicon is attributed to the strong elastic phonon-boundary scattering at the grain boundary. The thermal conductivity predicted from the multiscale modeling matches reasonably well with the measurement. This work provides insights into phonon transport in multiphase nanostructured materials and suggests that the effective thermal conductivity of nanostructured silicon from high-pressure torsion can be further reduced by increasing the volume fractions of the Si-III and Si-XII phases.

DOI： 10.1063/5.0037775

Language：English  

DOI： 10.1021/acs.langmuir.0c03208

Language：Others   Publishing type：Research paper (scientific journal)  

© 2020 Elsevier Inc. Si0.5Ge0.5 crystals were subjected to severe plastic deformation using high-pressure torsion (HPT). A metastable body-centered-cubic phase having a bc8 structure was formed by HPT processing with anvil rotations. High-resolution transmission electron microscopy analysis revealed that nanograins having diamond-cubic (dc) and bc8 phases were present in the HPT-processed sample. The bc8 phase was reverse transformed back to the dc phase after annealing. The resistivity of the crystalline Si0.5Ge0.5 (~9 × 10−3 Ω·cm) increased by roughly a factor of 6 after compression, and remained on the same order of magnitude but decreased slightly after 10 anvil rotations despite the grain refinement. These results indicate that the electrical behavior of bc8-Si0.5Ge0.5 is similar to that of bc8-Si.

DOI： 10.1016/j.matchar.2020.110590

Language：English   Publishing type：Research paper (scientific journal)  

The effect of thermally-insulating layer, particularly oxide layer as found in metallurgical applications, on the water spray-cooling process was discussed. Such layers have been found to increase the quenching temperature at which the sprayed liquid begins to contact the hot surface, greatly increasing the cooling rate. The conventional, thermal-resistance based model can predict the shift of the quenching point qualitatively, albeit significant deviations remain due to the lack of fundamental understanding of the onset of liquid-solid contact. In the present paper, we conducted two sets of experiments in an attempt to shed light on the quench mechanism and the effect of oxide layer. First, we compared temperature histories during spray cooling of a stainless-steel plate with various oxide layers. The quench temperatures varied depending both on the composition and the thickness of the oxide layer. Additionally, quench was observed at temperatures as high as 350 degrees C, exceeding the thermodynamic wetting limit. Then, we moved on to single droplet impingement experiments to investigate the change of droplet behavior with respect to the surface temperature in detail. High-speed imaging allowed us to identify the transition of droplet impact behavior i.e. deposition and bouncing, which also occurred at different wall temperatures depending on the composition of oxide layer. Subsequently, we calculated the contact surface temperature assuming the transient heat conduction for a contact between two semi-finite bodies. As a consequence, the onset of droplet behavior transition was always found at the contact surface temperature of ca. 250 degrees C regardless of the composition and thickness of the oxide layer. The difference between the contact surface temperature and the wall temperature increased as the thermal effusivity of the oxide layer decreased, which was a direct cause of the inconsistent "apparent" quenching temperature.

DOI： 10.1016/j.applthermaleng.2020.115682

Language：English  

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&#37; 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.

DOI： 10.1016/j.ijheatmasstransfer.2019.119274

Language：English  

Thermal contact resistance (TCR) between individual carbon fibers (CFs) can dominate heat dissipation rates in CF-based composite materials. Here, we develop a totally non-contact “laser-flash Raman mapping” method to simultaneously measure the TCR at the CF-CF junction and their thermal conductivities. Laser power is used to heat the sample and the laser absorptivity is experimentally determined by a transient laser-flash Raman technique. The laser heating positions are changed along two connected CFs, and the change of temperature rise with varying positions is in-situ measured from the temperature dependent Raman band shifts. The high spatial resolution of the micro-Raman mapping allows direct observation of the abrupt jump of thermal resistance at the CF-CF junction, from which we extracted the TCR as well as the thermal conductivity. The laser absorptivity of the 11 μm-diameter CFs is measured to be 0.12 ± 0.03, the thermal conductivities of the individual CFs are around 200 W/mK, and the TCR of the CF-CF junction is (2.98 ± 0.92) × 10⁵ K/W. This work provides indispensable knowledge for the design of CF-based composite for thermal management, and the novel non-contact measurement method can stimulate characterization and manipulation of contact/interface heat conduction between various micro- and nano-materials.

DOI： 10.1016/j.carbon.2018.09.034

Language：English   Publishing type：Research paper (scientific journal)  

Si (100) wafers with various doping levels were subjected to high-pressure torsion (HPT). The resistivities for all doping levels increased by one or two orders of magnitude after initial compression, but then decreased after 10 revolutions of HPT processing to similar to 0.1 Omega cm for normally and heavily doped samples, and to similar to 0.02 Omega cm for the ultraheavily doped sample. After annealing at 873 K, the resistivities increased by four orders of magnitude compared to the original Si wafers. These results indicate that the formation of metastable phases plays an important role in the electrical resistivities of HPT-processed samples. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2018.08.011

Language：English  

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.

DOI： 10.1016/j.ijheatmasstransfer.2018.05.023

Language：Others   Publishing type：Research paper (scientific journal)  

© 2018 Elsevier Ltd 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.

DOI： 10.1016/j.ijheatmasstransfer.2018.06.043

Language：Others   Publishing type：Research paper (scientific journal)  

© 2018 Elsevier Ltd 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.

DOI： 10.1016/j.ijheatmasstransfer.2018.06.030

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1615/IHTC16.bae.023953

Language：English   Publishing type：Research paper (other academic)  

Influence of localised heating on thermocapillary convection of pure water drops

Language：English   Publishing type：Research paper (scientific journal)  

Quantifying vapor transfer into evaporating ethanol drops in humid atmosphere

DOI： 10.1039/C8CP02521E

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.applthermaleng.2014.10.054

Language：Others   Publishing type：Research paper (scientific journal)  

© 2018 The Japan Society of Applied Physics. Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) and UNCD/non-hydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were prepared via coaxial arc plasma deposition, and their thermal conductivity and interfacial conductance in grain boundaries were measured using a time-domain thermoreflectance method. The interfacial conductance was estimated to be 1,010 and 4,892MW/(m2&K) for UNCD/a-C:H and UNCD/a-C films, respectively. The reasons for the hydrogenated film having lower interfacial conductance than the non-hydrogenated film are 1) the reduced number of carriers that contribute to heat transport and 2) the hydrogen atoms, which are preferentially located at the grain boundaries and enhance phonon scattering.

DOI： 10.7567/APEX.11.065101

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1063/1.5021240

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1299/jtst.2018jtst0011

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1615/ihtc16.bae.023482

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1615/ihtc16.bae.023953

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1615/ihtc16.tpm.023430

Language：Others   Publishing type：Research paper (scientific journal)  

© 2017 The Author(s). 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.

DOI： 10.1038/s41598-017-02163-8

Language：English   Publishing type：Research paper (scientific journal)  

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&#37;, spherical nanoparticle inclusions enhance the melting rate only by similar to 2&#37;. The inclusion of 1 vol&#37; loading of single-walled carbon nanotube and graphene nanoplatelets increases the melting rate by 27&#37; and 40&#37; respectively due to significant thermal conductivity enhancement of the nanocomposite compared to that of pure organic alkane. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2017.07.084

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 0.1016/j.ijheatmasstransfer.2017.08.078

Language：Others   Publishing type：Research paper (scientific journal)  

© 2017 American Chemical Society. 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&#37; (k = 2). The obtained PVT properties and vapor pressures are compared with the existing equation of state.

DOI： 10.1021/acs.jced.7b00263

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1021/acs.jced.7b00263

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.applthermaleng.2017.07.084

Language：English   Publishing type：Research paper (scientific journal)  

Influence of Local Heating on Marangoni Flows and Evaporation Kinetics of Pure Water Drops

DOI： 10.1021/acs.langmuir.7b00957

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.applthermaleng.2017.05.145

Language：English  

DOI： 10.1016/j.ijheatmasstransfer.2017.05.101

Language：English  

DOI： 10.1016/j.applthermaleng.2016.10.109

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.applthermaleng.2017.05.145

Language：English  

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&#37; and ∼25&#37; respectively at 1 vol&#37; loading as a result of higher thermal conductivity enhancement.

DOI： 10.1016/j.ijheatmasstransfer.2017.05.101

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.applthermaleng.2014.10.054

Language：English  

DOI： 10.1016/j.applthermaleng.2016.08.110

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijheatmasstransfer.2017.08.078

Language：English   Publishing type：Research paper (scientific journal)  

Language：Others   Publishing type：Research paper (scientific journal)  

© 2016 Hydrogen Energy Publications LLC 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.

DOI： 10.1016/j.ijhydene.2016.06.114

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

Induction of Marangoni convection in pure water drops

DOI： 10.1063/1.4966542

Language：English   Publishing type：Research paper (scientific journal)  

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&#37; graphene laoding, melting time reduces significantly by similar to 41&#37; when the HTF temperature is 60 degrees C and similar to 37&#37; when the HTF temperature is 70 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2016.06.166

Language：English  

DOI： 10.1016/j.ijheatmasstransfer.2016.05.132

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

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).

DOI： 10.1016/j.applthermaleng.2016.02.032

Language：English  

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.

DOI： 10.1080/01457632.2015.1067103

Language：English  

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.

DOI： 10.1116/1.4941308

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.applthermaleng.2016.02.032

Language：English  

Language：English   Publishing type：Research paper (other academic)  

The thermal conductivity of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition (CAPD) was measured by a timedomain thermoreflactance method. The specific heat and density of the films were measured to be 0.891 J/gK and 1.70 g/cm₃, respectively, as parameters for the estimation of the thermal conductivity. Based on them, the thermal conductivity was estimated to be 2.32 W/m-K. This value is smaller than that of general UNCD/a-C:H films prepared by chemical vapor deposition (CVD). It might be because the CAPD films possesses a huge number of grain boundaries owing to extremely small grains of approximately 2.3 nm as compared with those of CVD films and its structure enhances phonon scattering.

DOI： 10.1149/07525.0027ecst

Language：English   Publishing type：Research paper (other academic)  

Language：English  

Language：Others   Publishing type：Research paper (scientific journal)  

© 2015 Elsevier Ltd All rights reserved. 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&#37; (k = 2).

DOI： 10.1016/j.jct.2015.04.028

Language：English   Publishing type：Research paper (scientific journal)  

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).

DOI： 10.1016/j.jct.2015.04.028

Language：English  

Language：English  

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&#37; at a loading of 1 vol&#37;. 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.

DOI： 10.1016/j.applthermaleng.2015.01.056

Language：English  

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.

DOI： 10.1021/jp512735k

Language：English  

Language：English  

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&#37; is found to be ∼37 and ∼11&#37;, 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.

DOI： 10.1016/j.tca.2014.12.004

Language：English  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Development of Gas Viscosity Measurement System with Vibrating Wire Method

DOI： 10.2963/jjtp.28.15

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Others   Publishing type：Research paper (scientific journal)  

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. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2014.05.031

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1186/1556-276X-9-326

Language：English  

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.

DOI： 10.1016/j.ijhydene.2014.02.063

Language：Others   Publishing type：Research paper (scientific journal)  

© 2014 Elsevier Ltd. 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.

DOI： 10.1016/j.applthermaleng.2014.10.054

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Language：English  

Language：English  

We recently reported that laser irradiation of aerosol amorphous carbon nanoparticles induces formation of onion-like carbon structures. In this study, the further analyses of laser induced phase transitions and restructuring of aerosol carbon nanoparticles were carried out using the combination of off-line and in-flight measurement techniques. Laser-synthesized carbon agglomerates composed of 7-nm amorphous primary nanoparticles were used as starting materials. Irradiation of multiple laser shots to the gas-suspended carbon agglomerates resulted in the formation of variety of unique structures, such as diamond-like, defective graphite, concentric shell structures, and their agglomerates. Evolutions of the carbon nanostructures were found to be responsible for the in-flight mass-to-mobility spectra.

DOI： 10.1016/j.carbon.2013.12.111

Language：English  

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.

DOI： 10.1016/j.ijheatmasstransfer.2013.12.066

Language：English  

Language：Japanese  

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2014-21468

Language：English  

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.

DOI： 10.1080/01457632.2013.812496

Language：English  

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.

Language：English   Publishing type：Research paper (scientific journal)  

Thin metal films are widely used as interconnecting wires and coatings in electronic devices and optical components. Reliable thermophysical properties of the films are required from the viewpoint of thermal management. The cross plane thermal transport of four polycrystalline molybdenum nanofilms with different thickness deposited on glass substrates has been studied by applying the picosecond laser transient thermoreflectance technique. The measurement is performed by applying both front pump-front probe and rear pump-front probe configurations with high quality signal. The determined cross plane thermal diffusivity of the Mo films greatly decreases compared to the corresponding bulk value and tends to increase as films become thicker, exhibiting significant size effect. The main mechanism responsible for the thermal diffusivity decrease of the present polycrystalline Mo nanofilms is the grain boundary scattering on the free electrons. Comparing the cross plane thermal diffusivity and inplane electrical conductivity indicates the anisotropy of the transport properties of the Mo films.

DOI： 10.1155/2014/578758

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2014-21468

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2013-73069

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1299/jtst.8.603

Language：English   Publishing type：Research paper (other academic)  

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%.

DOI： 10.1115/ICNMM2013-73139

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

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Bessel beam has been gaining strong attention from various applications. In this study, a new concept for generating zero-order Bessel beams was studied theoretically and experimentally. The principle of the generation of a Bessel-like beam is discussed based on Fourier optics. A preliminary model is proposed that accounts for heat conduction and diffraction effect. Analytical modeling results indicated that Bessel beam can be generated by using a thermal lens and a convergent lens. A simple and flexible method to convert a Gaussian laser beam into a Bessel-like beam with a long and narrow focal line by using a thermal lens effect is demonstrated experimentally. Experimental and calculated results show a good agreement for generation and characteristics of Bessel-like beam. Experimental results also show that the focal depth of the Bessel beam can be controlled by adjusting some parameters in the thermal lens system. The paper concludes with suggestions for further research and potential applications for the work.

DOI： 10.1299/kikaib.79.1354

Language：English  

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.

DOI： 10.1299/jtst.8.294

Language：English  

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.

DOI： 10.1016/j.ijthermalsci.2013.03.004

Language：English  

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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&#37;.

DOI： 10.1016/j.expthermflusci.2012.11.008

Language：English  

Language：English  

The seventh U.S.-Japan Joint Seminar on Nanoscale Transport Phenomena was held in Shima, Japan, from December 11 to 14, 2011. The goals of this joint seminar were to provide a critical assessment of the state of the art and future directions in the field of nanoscale transport phenomena and energy conversion processes, to foster U.S.-Japan collaborations, and to provide international exposure to a new generation of scientists in this field. Issues discussed in the joint seminar were organized in 10 topical sessions, including (1) nanoscale thermophysical measurements; (2) optical characterization; (3) thermal and molecular transport; (4) phonon transport modeling; (5) energy storage and conversion; (6) nanoscale fluidics and phase change phenomena; (7) biological and organic systems; (8) interfacial thermal transport; (9) novel thermoelectric and thermal management materials; and (10) nanocarbon materials and devices. In addition to these topical sessions, the joint seminar featured an opening plenary session and a closing plenary session as well as an expert panel, where leading experts provided critical assessment of the past progress and addressed future directions in the field. In addition, an evening poster session provided opportunities for graduate and postdoc students to present their latest research results. About 35 researchers from Japan and 31 researchers from the United States participated in the meeting. The meeting was organized by S. Maruyama, K. Fushinobu, L. Shi, and J. Lukes together with about 20 other participants who served as session chairs. Summaries of different sessions of the seminar were prepared by the session and conference chairs and are collected into this report.

DOI： 10.1080/15567265.2012.745913

Language：English  

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.

DOI： 10.1016/j.ijthermalsci.2012.07.014

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2012-73135

Language：Japanese  

An apparatus for measuring PVT properties of hydrogen was developed on the basis of the isochoric method in the temperature range from 473 K to 773 K and at pressures up to 100 MPa. Due to very low hydrogen density, it is difficult to measure the mass of sample in the sample cell (250 cc) accurately, and hence an expansion cell with a large volume (2500 cc) was equipped to combine with the gas expansion method to determine the initial densities of the isochors. To confirm the validity of this apparatus, nitrogen was first measured from 473 K to 773 K and up to 100 MPa. The obtained data are in good agreement with a reference equation of state for nitrogen within 0.1 &#37;. Finally, we measured the PVT properties of hydrogen at 473 K and up to 100 MPa. The present data agree with the data obtained by the Burnett method within 0.1 &#37;.

DOI： 10.2963/jjtp.26.86

Language：Japanese  

Language：Others   Publishing type：Research paper (scientific journal)  

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&#37; to 0.24&#37; (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&#37;(k = 2) at P ≤ 15MPa, 0.20 &#37; at 15 MPa < P ≤ 40 MPa, and 0.24 &#37; 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&#37; above 300K and up to 100MPa, while at lower temperatures, as the pressure increases, the deviations become larger (up to 1.5 &#37;). © Springer Science+Business Media, LLC 2012.

DOI： 10.1007/s10765-012-1168-2

Language：Others   Publishing type：Research paper (scientific journal)  

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&#37; to 0.24&#37; (k = 2), both with the latest equation of state and existing measured data. © Springer Science+Business Media, LLC 2011.

DOI： 10.1007/s10765-011-1120-x

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1115/1.4004937

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2011-58205

Language：English   Publishing type：Research paper (other academic)  

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%.

Language：English   Publishing type：Research paper (other academic)  

Considering the massive-scale synthesis of single-walled carbon nanotube (SWCNT), chemical vapor deposition has become a standard process for synthesizing CNTs. In most of these processes, oxygen and hydrogen atoms were included originally or added later; and they are expected to have important roles such that they helped in the removal of amorphous carbon and prevented SWCNTs from containing metal particles. However, whole perspectives for suitable carbon source or ideal balance among carbon, hydrogen, and oxygen have not been reported. We examined a variety of raw materials in our newly developed round-trip-type vacuum furnace in order to determine whether they could be used to synthesize a carbon nanotube. We used Raman spectroscopy for evaluation, and plotted the component ratios of effective and ineffective materials on a C-H-O ternary diagram. Consequently, it is clear that the growth region should satisfy the equation O < C < (H + O) in molar ratio.

Language：English   Publishing type：Research paper (other academic)  

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.

Language：English   Publishing type：Research paper (scientific journal)  

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. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.cryogenics.2011.09.001

Language：English  

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 &#37; (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 &#37;.

DOI： 10.1007/s10765-011-1052-5

Language：English  

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&#37; compared with a correlation developed by the present authors and with REFPROP (NIST).

DOI： 10.1007/s10765-011-0999-6

Language：English  

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&#37;.

DOI： 10.1080/08916152.2010.503310

Language：English  

Language：English  

Language：English  

Language：English  

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&#37; to 12&#37;. Also, the comparison between the obtained results and the results due to others shows a good agreement with difference ranged from 5&#37; to 16&#37;. 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.

DOI： 10.1016/j.ijheatfluidflow.2010.08.005

Language：English  

Language：English  

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.

DOI： 10.1007/s12206-010-1110-0

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ajtec2011-44414

Language：English   Publishing type：Research paper (other academic)  

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%.

DOI： 10.1115/ajtec2011-44415

Language：English   Publishing type：Research paper (other academic)  

Considering the massive-scale synthesis of single-walled carbon nanotube (SWCNT), chemical vapor deposition has become a standard process for synthesizing CNTs. In most of these processes, oxygen and hydrogen atoms were included originally or added later; and they are expected to have important roles such that they helped in the removal of amorphous carbon and prevented SWCNTs from containing metal particles. However, whole perspectives for suitable carbon source or ideal balance among carbon, hydrogen, and oxygen have not been reported. We examined a variety of raw materials in our newly developed round-trip-type vacuum furnace in order to determine whether they could be used to synthesize a carbon nanotube. We used Raman spectroscopy for evaluation, and plotted the component ratios of effective and ineffective materials on a C-H-O ternary diagram. Consequently, it is clear that the growth region should satisfy the equation O < C < (H + O) in molar ratio.

DOI： 10.1115/ajtec2011-44193

Language：English  

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/FEDSM-ICNMM2010-30127

Language：English  

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&#37; to 25&#37;.

DOI： 10.1016/j.ijthermalsci.2010.08.008

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

This study examines the performance of a wire-type Joule Thomson microcooler utilizing a flexible concentric counterflow heat exchanger. Three gases: C(2)H(4), CO(2) and N(2) were used separately for trials conducted at inlet pressures ranging from 0.5 MPa to 5 MPa with C(2)H(4) having the best performance. During unloaded tests at an inlet pressure of 2.0 MPa, C(2)H(4) obtained a minimum temperature of 225 K while CO(2) obtained a minimum temperature of 232 K. Using CO(2) 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. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2010.07.007

Language：English  

Chemical vapor deposition has become a standard process for synthesizing carbon nanotubes. Since the successful use of chemical vapor deposition for the first time, much effort has been expended into exploring various carbon sources that can be used to synthesize carbon nanotubes, such as methane, ethane, and ethanol. However, whole perspectives for suitable carbon sources have not been clear. In this study, we performed experiments in order to determine that the appropriate C-H-O components ratio in raw materials can be used to synthesize carbon nanotubes. We also examined a variety of raw materials in our newly developed round-trip-type vacuum furnace in order to determine whether they could be used to synthesize a carbon nanotube. We used Raman spectroscopy to identify the developed carbon nanotube, and we plotted the component ratios of effective and ineffective materials on a C-H-O ternary diagram; in this diagram, the growth region became highly apparent. It should be noted that for the growth of the carbon nanotube, this region should satisfy the equation O < C < (H + O) in molar ratio. Furthermore, it was observed that adjusting the component ratios by mixing raw materials did not cause an inconsistency in the growth region.

DOI： 10.1016/j.diamond.2010.08.005

Language：English  

Language：English  

Language：English  

Gas suspended single-walled carbon nanotubes (SWCNTs) with single tube diameter smaller than 2 nm and length of longer than 500 nm were generated by simple and continuous system using laser ablation technique under atmospheric conditions. Graphite target containing 0.5 wt&#37;-nickel and 0.5 wt&#37;-cobalt was ablated by Nd:YAG laser in an electrical furnace under atmospheric pressure of nitrogen flow that allowed one step and continuous synthesis of the SWCNTs. Size distribution of the gas suspended SWCNTs aerosol was measured using size-classification by a differential mobility analyzer (DMA) coupled with a condensation particle counter (CPC) used as a detector. Characteristics of SWCNT aerosol generated under the different temperature were also investigated using scanning and transmission electron microscopes and Raman scattering. Mono-mobility SWCNT aerosol with mobility diameter of 100 and 200 nm was successfully prepared after the size separation using a DMA.

DOI： 10.1007/s11051-010-9847-z

Language：English  

Language：English  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Development of a PVT Property Measurement Apparatus by the Burnett Method for High Pressure Hydrogen

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1007/s10765-009-0699-7

Language：Others   Publishing type：Research paper (scientific journal)  

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. © Springer Science+Business Media, LLC 2010.

DOI： 10.1007/s10765-009-0699-7

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/MNHMT2009-18068

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2009-82215

Language：English  

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.

DOI： 10.1007/s10765-009-0668-1

Language：English  

Language：English  

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.

DOI： 10.1007/s10765-009-0572-8

Language：English  

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.

DOI： 10.1080/01457630802594820

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1299/jtst.4.146

Language：English   Publishing type：Research paper (scientific journal)  

A PVT measurement apparatus by the Burnett method for the temperature range from room temperature to 250 ℃ and at pressures up to 100 MPa has been developed with a remote operation system. PVT measurements of hydrogen, helium and nitrogen have been accomplished up to 97 MPa. The density uncertainty of the present measurements at 80 ℃ is estimated to be 0.2 % from the deviations for nitrogen. An existing equation of state (EOS) for hydrogen agrees well with the present measurements within ±0.22 % at 80 ℃. The systematic deviations between the EOS and the present measurements at 120 ℃ and 160 ℃ are shown with the maximum deviation of 0.52 % at 120 ℃ and 97 MPa.

DOI： 10.1299/jsmeicope.2009.2._2-265_

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2008-62082

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English  

Language：English  

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/ICNMM2007-30108

Language：English  

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.

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

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.

DOI： 10.1088/1742-6596/59/1/033

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1115/HT2007-32776

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Mass-selected silicon cluster ions were levitated in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer and monitored during chemisorption reaction with ethylene (C₂H₄). Through measurements of "time-dependency" of this reaction process, large change of the reactivity depending on the number of absorbed ethylene was observed, in addition to the strong dependency to silicon cluster size. From Si₁₅⁺ to Si₁₈⁺ shows a special stability of Si_xE_y⁺ when x + y = 19, such as Si₁₅E₄⁺. The large decrease in the reactivity of Si_n⁺ was observed due to the contamination of hydrogen atom to Si_n⁺. Rate constants for the adsorption of the first C₂H₄ molecules on Si_n⁺ were estimated. The reaction kinetics data suggest that structural isomers are present for all clusters except Si₁₄⁺ in the size range investigated.

DOI： 10.1299/kikaib.71.1148

Language：English  

DOI： 10.1016/j.elspec.2004.09.016

Language：Japanese  

Language：English  

Laser microfabrication using a diffraction-free beam (Bessel beam) was performed. Microfabrication with a deep focal depth is possible because a diffraction-free beam has a main lobe with a small diameter, which does not depend on propagation length. The diffraction-free beam was generated using an axicon lens, and the generation was confirmed using an optical microscopy image of a laser-fabricated spot on a silicon wafer. Nevertheless using a nanosecond pulsed Nd:YAG laser, microfabrication with a spot diameter < 1 μm was realized. As a result of the deep focal depth of the diffraction-free beam, even if we change the work distance within a range of several millimeters, we are still able to maintain the diameter of the laser- fabricated spots to approximately 1 μm. Since an almost straight penetration hole with a diameter of 3 μm was drilled into SUS304 foil (20 μm thick), it was found that the diffraction-free beam has a high feasibility for the high-aspect-ratio laser drilling of an opaque material due to its deep focal depth.

DOI： 10.1299/jsmeb.47.497

Language：Japanese  

Language：English  

Single-walled carbon nanotubes (SWNTs) were synthesized using size-controlled catalyst nanoparticles created by the pulsed laser ablation method. Specifically, the alloy particles (Co/Mo or Co/Pt) were prepared by ablation of the target alloy materials in an inert gas atmosphere. Size selection was performed using a differential mobility analyzer (DMA). The obtained nanoparticles were deposited on a quartz substrate from which SWNTs were grown by the alcohol catalytic CVD (ACCVD) technique that was developed by the authors' group. AFM and Raman scattering analysis revealed that SWNTs were successfully synthesized. It seems the Co/Mo alloy catalyst was more effective for the synthesis of SWNTs than the Co/Pt catalyst, though this is a preliminary result to be further investigated.

DOI： 10.1007/s00339-004-2756-1

Language：English  

A semi-continuous process for the synthesis of fullerenes is described. This novel process incorporated a carbon powder feed system in combination with a continuous-wave CO₂ laser irradiation source. The carbon powder contained no fullerenes but did contain graphite crystals and amorphous carbons of selected particle sizes (5, 10, or 20 μm), and selected irregular or spherical particle shapes. The method was successfully used to deposit C₆₀ and C₇₀ powders and films continuously. Laser irradiation of the carbon powder produced an observable laser plume. The experimental results and mechanism for the process are discussed.

DOI： 10.1117/12.478570

Language：English  

A process was investigated to irradiate a continuous-wave CO₂ laser (4.5 kW) on graphite powder with a mean diameter of 5 μm in a flow of Ar or He gas at 30 or 200 Torr. The film produced on a Ni substrate in the Ar flow at 200 Torr showed the Raman bands of C₆₀ and C₇₀, and the C₆₀/C₇₀ ratio was estimated to be 5/1 by MALDI-TOF mass spectrometry. The film formation process is discussed on the basis of an analysis of laser-irradiated powder, which included 0.01 wt&#37; of C₆₀, by UV-Vis absorption, and by observations of the plumes and SEM images.

DOI： 10.1016/S0009-2614(03)01326-5

Language：English  

Chemical reaction of small silicon cluster ions (Si_n⁺:13, 15 ≤i ni ≤i 29) with nitric oxide was studied by using the FT-ICR (Fourier Transform Ion Cyclotron Resonance) mass spectrometer. Silicon clusters were generated by a pulsed laser-vaporization supersonic-expansion cluster beam source directly connected to the FT-ICR mass spectrometer. Fully thermalized and mass-selected clusters were reacted with NO in the ICR cell. The primary reaction was the exchange of a silicon atom with a nitrogen atom as Si_n⁺ + NO → Si_n-1N⁺ + SiO. Then, smaller clusters than Si₂₃N⁺ (with exceptions for Si₁₆N⁺ and Si₂₀N⁺) fragmented to much smaller clusters. It was explained that in general smaller clusters could not survive with the exothermal reaction heat. On the other hand, the magic number clusters of Si₁₆N⁺ and Si₂₀N⁺ probably represented the geometrical special stability.

DOI： 10.1299/kikaib.69.1879

Language：English  

Metal-carbon binary clusters are believed to be important precursor clusters both for single-walled carbon nanotubes (SWNTs) and endohedral metallofullerene. Metal-carbon binary clusters (MC_n M = La, Ni or Co) and carbon clusters (C_n) were generated with a pulsed laser-vaporization supersonic-expansion cluster beam source directly connected to the FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometer, and chemical reaction of MC_n^- and C_n^- with nitric oxide was studied. Depending on the metal element, the generation efficiency and the reactivity of metal-carbon binary clusters were completely different. LaC_n^- (n=even, n≥36) was much less reactive to NO than pure carbon clusters, while MC_n^- (M = Ni or Co) was much more reactive than pure carbon clusters. It was speculated that LaC_n^- (n=even, n≥36) had a fullerene-like cage structure with a metal atom inside, and that MC_n^- (M = Ni or Co) had an imperfect cage structure where a metal atom preferentially attached to the imperfect site.

DOI： 10.1299/kikaib.69.1886

Language：English  

By using alcohol such as ethanol and methanol as the carbon source, a new simple catalytic chemical vapor deposition technique to generate high-purity single-walled carbon nanotubes at low temperature is demonstrated. Vapor phase alcohol was supplied over Fe/Co catalyst supported with Zeolite in an electric furnace. The blackened sample was analyzed by resonant Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. Because of the etching effect of decomposed OH radical attacking carbon atoms with a dangling bond, impurities such as amorphous carbon, multi-walled carbon nanotubes, metal particles and carbon nanoparticles are completely suppressed even at relatively low reaction temperature such as 700-800°C.

DOI： 10.1299/kikaib.69.918

Language：Japanese  

Language：English  

Metal-carbon binary clusters generated by the laser vaporization of Ni/Co and Ni/Y doped graphite samples used for the macroscopic laser-oven production of SWNTs were studied. Positive and negative clusters generated by the laser-vaporization supersonic-expansion cluster beam source were directly injected into the FT-ICR (Fourier Transform Ion Cyclotron Resonance) mass spectrometer. Depending on the metal species, the generation efficiency of metal-carbon binary clusters was drastically different. The chemical reaction of these clusters with NO gas was used as the probe of the geometrical structure of clusters. The reactivity to NO of these binary clusters was completely different. In case of YC_n (n = even, n ≥ 36), chemical reaction of YC_n with NO was not observed while pure carbon clusters were reacted. On the other hand, for MC_n (M = Ni or Co), the reactivity was much higher than pure carbon clusters. It was speculated that a few Ni or Co atoms attached outside of imperfect carbon cage for Ni/Co doped case and that Y atom was included in the carbon cage for Ni/Y doped case.

DOI： 10.1080/10893950390150458

Language：Japanese  

Language：English  

Language：English  

Metal-carbon binary clusters generated by the laser vaporization of Ni/Co- and Ni/Y-loaded graphite samples used for the macroscopic production of SWNTs were studied. Positive and negative clusters generated by the laser-vaporization supersonic-expansion cluster beam source were directly injected into the FT-ICR mass spectrometer. The chemical reaction of these clusters with NO was used as the probe of the geometrical structure of clusters. It was speculated that a few Ni or Co atoms attached outside of imperfect carbon cage for Ni/Co loaded case, and that Y atom was included in the carbon cage for Ni/Y loaded case.

DOI： 10.1016/S0921-4526(02)00996-1

Language：English  

By using alcohol as the carbon source, a new simple catalytic chemical vapor deposition technique to synthesize high-purity single-walled carbon nanotubes at low temperature is demonstrated. Because of the etching effect of decomposed OH radical attacking carbon atoms with a dangling bond, impurities such as amorphous carbon, multi-walled carbon nanotubes, metal particles and carbon nanoparticles are completely suppressed even at relatively low reaction temperature such as 700-800 °C. By using methanol, generation of SWNTs even at 550 °C is demonstrated. The high-purity synthesis at low temperature promises large scale production at low cost and the direct growth of SWNTs on conventional semiconductor devices already patterned with aluminum.

DOI： 10.1016/S0009-2614(02)00838-2

Language：English  

Language：English  

Photoelectron spectra of metal-attached carbon cluster anions MC_n^- (M = Sc, Y, and La, 5≤n≤20) generated in a laser-vaporization ion source were measured using a magnetic bottle time-of-flight photoelectron spectrometer with 6.4 eV photon energy. The vertical detachment energy (vDE) of each species was estimated from the spectra and compared with the vDE of the linear and monocyclic ring forms of C_n. It was found that PES features of MC_n^- (5≤n≤20, n = odd) could be understood under the assumption that the π electronic structure of MC_n^- is similar to those of the linear carbon chains. However, the PES features of MC_n^- (12≤n≤20, n = even) indicate the presence of a π electronic structure similar to the isomers having ring form. Further possible electronic and molecular structures are presented and discussed for MC_n^- of odd n and even n, respectively.

DOI： 10.1016/S0368-2048(00)00210-3

Language：English  

The photoelectron spectra of C^-₆₀ produced with three different generation methods were recorded with 6.4eV photon energy using a magnetic-bottle-type time-of-flight photoelectron spectrometer. From these spectra, it was suggested that the laser vaporization of a graphite rod mainly produces C^-₆₀ of ring-like structure. On the other hand, C^-₆₀ produced by the fragmentation process of the fullerene C₇₀ through C₂ or C_2n elimination give different photoelectron features from those of C^-₆₀ having an icosahedral (I_h) symmetry or a ring-like structure.

DOI： 10.1007/s100530050456

Language：English  

For experimental treatments of atomic clusters, a FT-ICR (Fourier Transform Ion Cyclotron Resonance) spectrometer with a direct injection supersonic cluster beam source was implemented. Newly designed ICR cell in 6 Tesla superconducting magnet was proved to give a high mass-resolution for positive and negative cluster ions. With this mass-spectrometer, pure carbon and metal-carbon binary clusters generated by the laser-vaporization supersonic-expansion cluster-beam source were studied. A special cluster beam source condition was found where only C₆₀⁺ was observed for pure carbon clusters. Furthermore, positive lanthanum-carbon, yttrium-carbon and scandium-carbon binary clusters showed only MC_2n⁺ signal in the range of 36≤2n≤76 with strong magic numbers at MC ₄₄⁺, MC₅₀⁺ and MC₆₀ ⁺. Characteristics of these small clusters were compared with results of molecular dynamics simulations.

DOI： 10.1299/kikaib.65.3791

Language：English  

Photoelectron spectroscopy was applied to characterize electronically excited states of carbon clusters consisting of odd number atoms, C^-
_2n-1 (n = 2-7). By optimizing the cluster generation condition so that the fraction of C^-
_n anions with a linear form increases, the energy difference between the ground and the first excited states of the carbon linear chains up to C^-
₁₅ was systematically examined. As a result, it was found that the photoelectron second bands are attributed to the first excited triplet states of neutral carbon linear chains. The monotonous decrease of the excitation energy found for C_7-15 clearly indicates that these linear chains possess a common electronic property for the lowest triplet states. Furthermore, by analyzing the decrease of the excitation energy in the triplet manifold, it was found that the gap tends to converge to almost zero by increasing a length of carbon chain.

DOI： 10.1063/1.478269

Language：English  

Language：English  

The formation mechanism of empty and metal-containing fullerene was studied through MD (molecular dynamics) simulations and FT-ICR (Fourier transform ion cyclotron resonance) mass spectroscopy of laser vaporized carbon cluster. Multi-body classical potential functions for metal-carbon and metal-metal interactions were constructed based on DFT (density functional theory) calculations of various forms of small clusters MC_n and M_n (M = La, Sc, Ni). Using the modified Brenner potential for carbon-carbon interaction, the clustering process starting from 500 isolated carbon atoms and 5 metal atoms in gas phase was simulated under the controlled temperature condition at 3000K. The difference of clustering process of LaC_n, ScC_n and NiC_n were compared with empty fullerene formation simulation. FT-ICR mass spectrometer directly connected to the laser vaporization cluster beam source was implemented in order to experimentally study the clustering process. The increase of cluster nozzle pressure roughly corresponded to the later stage of the molecular dynamics simulation. The FT-ICR mass spectra of metal-carbon composite clusters were compared for various sample materials used for arc-discharge generation of metal-containing fullerene and SWNT (single-wall carbon nanotube); La, Y, Sc, Gd, Ce, Ca, and Ni-Y. Positive La-C, Y-C, Sc-C, Gd-C, Ce-C binary clusters commonly showed strong MC_2n⁺ signal in the range of 36 < 2n with intense magic numbers at MC₄₄⁺, MC₅₀⁺ and MC₆₀⁺. It was speculated that the even-numbered clusters corresponded to the annealed random caged clusters observed in the MD simulation.

DOI： 10.1080/10641229909351366

Language：Japanese  

Language：English  

Language：English  

A photoelectron spectroscopy technique was successfully applied to the detection and characterization of a linear conformer of negatively-charged carbon clusters from C₁₀^- to C₁₆^-. By controlling the laser fluence for vaporization it was found that the fraction of a linear conformer was enriched. The presence of the linear form up to C₁₆^- was confirmed by the photoelectron spectroscopic evidences. On the basis of the present observations, it was also found that the observed vertical electron affinity up to C₁₆ shows a distinct even-odd alternation, converging into the asymptotic value of ca. 5.0 eV.

DOI： 10.1016/S0009-2614(97)01273-6

Language：English  

Language：English  

Language：English  

n-Dehydroannulenes with the ring size of n= 12, 16, 18, 20, and 24 and with three to five indanyl substituents are laser ablated by 355 nm photons. The indanyl unit is lost stepwise up to the complete deletion to leave the bare annulenyl skeleton. The monoanions of these products are mass analyzed first, and then subjected to a second laser pulse of 266 nm to obtain photoelectron spectra for C^-_n with n=12, 16, 18, 20, and 24. The spectra are compared with those obtained by using graphite as a target of the laser ablation. The comparison of the two spectra provides useful information on the structure of neutral carbon clusters.

DOI： 10.1063/1.474841

Language：English  

Language：English  

The mass distribution of neutral carbon clusters generated by a laser vaporization of graphite in He was safely determined by a single photon (10.5 eV) ionization technique. The resulting mass distribution was surprisingly different from those reported in previous articles. It was found that the carbon clusters generated under a moderate laser fluence condition (0.1-1 J/cm²) consists of mostly even-numbered monocyclic rings with the cluster sizes of n = 10-18. The formation mechanism of such neutral carbon clusters upon laser irradiation is discussed.

DOI： 10.1063/1.473883

Language：English  

Mass spectra of LaC_n^- were taken by using a laser-vaporization source (LVS) and pulsed arc cluster ion source (PACIS) applied to La-carbon composite rods (1:130 atomic ratio). The mass spectrum using the LVS with annealing procedure has shown several magic numbers for LaC_n^- (n = 44, 50, 60, and 70), whereas only small LaC_n^- (up to n = 14) have been observed in the mass spectrum using the PACIS. Photoelectron spectra of some of these have been measured using a magnetic-bottle type time-of-flight electron spectrometer. These results indicate the exsistence of a few conformational isomers for small La-containing carbon cluster negative ions LaC_n^- (n = 5-8).

DOI： 10.1007/s004600050238

Event date： 2010.5

Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2010.3

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Event date： 2024.6

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Event date： 2023.10

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Venue：Edinburgh   Country：United Kingdom  

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Venue：福岡市，佐賀市   Country：Japan  

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Event date： 2022.10 - 2021.10

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Venue：和歌山（オンライン）   Country：Japan  

Event date： 2022.10 - 2021.10

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Event date： 2020.10

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Event date： 2017.10

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Venue：Jeju   Country：Korea, Republic of  

Event date： 2017.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Event date： 2017.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Event date： 2017.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Event date： 2017.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀   Country：Japan  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀   Country：Japan  

Event date： 2016.12

Language：English  

Venue：Tokyo   Country：Japan  

Event date： 2016.12

Language：English  

Venue：Tokyo   Country：Japan  

Event date： 2016.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山   Country：Japan  

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：松山   Country：Japan  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：松山   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：仙台   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2016.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Daejeon   Country：Korea, Republic of  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Krakov   Country：Poland  

Event date： 2016.5

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2016.5

Language：English   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2016.5

Language：English   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2016.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2016.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2016.5

Language：English   Presentation type：Oral presentation (general)  

Venue：San Sebastian   Country：Spain  

Event date： 2016.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Waikoloa   Country：United States  

Event date： 2016.3

Language：English   Presentation type：Oral presentation (general)  

Venue：ハワイ島   Country：United States  

Event date： 2016.3

Language：English   Presentation type：Oral presentation (general)  

Venue：ハワイ島   Country：United States  

Event date： 2016.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Waikoloa   Country：United States  

Event date： 2015.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2015.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台   Country：Japan  

Event date： 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長崎   Country：Japan  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2015.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Edinburgh   Country：United Kingdom  

Event date： 2015.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Event date： 2015.7

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2015.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Boulder   Country：United States  

Event date： 2015.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2015.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2015.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2015.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Calgary   Country：Canada  

Event date： 2015.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Phuket   Country：Thailand  

In this work effect of ambient humidity of water vapor on evaporation of sessile drops of ethanol and methanol on a copper substrate is experimentally investigated. Experiments are conducted in a temperature and humidity controlled environmental chamber. An infrared (IR) camera and CCD camera are used to measure thermal distributions and profile change of the evaporating droplet, respectively.Results show that average temperature at the liquid–vapor interface increases when increasing relative humidity. Furthermore, evaporation rate decreases with relative humidity. A residual liquid is observed after ethanol/methanol evaporation, which is considered to be water adsorbed from the ambience into the droplet.

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Kurabi   Country：Thailand  

Event date： 2014.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Kurabi   Country：Thailand  

Event date： 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Event date： 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Chicago   Country：United States  

Event date： 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Chicago   Country：United States  

Event date： 2014.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Santa Cruz   Country：United States  

Event date： 2014.6 - 2014.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Krakow   Country：Poland  

Event date： 2014.5

Language：English   Presentation type：Oral presentation (general)  

Venue：上海   Country：China  

Event date： 2013.11 - 2013.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

Event date： 2013.11 - 2013.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

Event date： 2013.11 - 2013.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

Event date： 2013.11 - 2013.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

Event date： 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：宇部   Country：Japan  

Event date： 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：宇部   Country：Japan  

Event date： 2013.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：弘前   Country：Japan  

Event date： 2013.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：弘前   Country：Japan  

Event date： 2013.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Event date： 2013.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)