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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijheatmasstransfer.2023.124420

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Repository Public URL： https://hdl.handle.net/2324/7178892

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

In this study, the characteristics of disturbance waves, including velocity, longitudinal size, and frequency, are comprehensively investigated by conducting gas–liquid upward annular flow experiments in a 5 mm tube through the constant electric current method (CECM). The film thickness time trace is recorded with respect to time, and the information on disturbance waves is subsequently extracted. The effect of liquid and gas flow rate, density ratio, and surface tension on the disturbance wave is quantitatively analyzed. A predictive model of the wave velocity based on the shear stress balance of the liquid film is proposed. A physical model for wave frequency prediction is derived on the basis of the mass conservation equation. A simple empirical model with good prediction accuracy of wave frequency is also derived. Compared with existing correlations available in the literature, the newly derived models show better performance under a wide range of flow conditions.

DOI： 10.1016/j.ijheatmasstransfer.2023.124253

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Repository Public URL： https://hdl.handle.net/2324/7178891

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

The wetting velocity that is the propagation velocity of a liquid film falling along a high temperature wall is of considerable importance in a variety of technical applications such as emergency core cooling in nuclear power plant, heat exchangers, and metallurgical processes. To predict the wetting velocity, the quenching model that consists of the heat transfer coefficient (HTC) distribution and the quenching temperature is needed. Since direct measurements of these quantities were technically difficult, most of the existing quenching models were developed so as to match the calculated wetting velocity with the experimental data. It was therefore unknown if the existing models can be applied to the conditions under which their predictive performance was not tested. In this work, to develop a new quenching model that is applicable in wide range of experimental conditions, transient of the wall temperature profile during quenching was measured using a high-speed infrared camera. A silicon wafer that was transparent against infrared rays was utilized as the wall. In addition, a normal high-speed camera was used to understand the hydrodynamic phenomena encountered during quenching. As a result, it was found that nucleate boiling in the liquid film was the main heat transfer mechanism near the wetting front and the width of the area where significant heat transfer occurred was in the same order of magnitude as the size of nucleation bubbles. Based on these findings, a phenomenological quenching model was developed. It was shown that the present model predicts the wetting velocity more accurately than the existing ones not only for the present data but also for those accumulated in different conditions. It was hence considered that the present model well describes the thermal-hydraulic phenomena encountered near the wetting front during quenching.

DOI： 10.1016/j.applthermaleng.2023.120210

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Repository Public URL： https://hdl.handle.net/2324/7178893

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>To promote the "Basic Hydrogen Strategy" first formulated by Japan [1], hydrogen storage technology based on toluene and methylcyclohexane (MCH) reversible reaction has received widespread attention due to its convenience in hydrogen transport. Superheated vaporization is a necessary process for the catalytic dehydrogenation of MCH, and a novel method with a simple structure to generate superheated water steam quickly and efficiently have been proved in our previous study. However, the start-up response and efficiency of this porous media steam generator has not yet been clarified while using organic fluid. As MCH is toxic to human body, ethanol, which has similar physical properties to MCH, was used in our experiment. Compared to the water, ethanol with lower latent heat has better performance in generating superheated vapor rapidly and efficiently, which also proves that the proposed vapor generator is suitable for the MCH reaction. Considering both heat transfer and fluid flow in the porous media, the energy utilization efficiency and surface temperature were analyzed using one-dimensional models.</p>

DOI： 10.1299/jsmepes.2023.27.b122

CiNii Research

Language：English   Publisher：The Japan Society of Mechanical Engineers  

<p>Enhancement of pool boiling heat transfer using a copper honeycomb porous plate (HPP) made by electrolytic deposition has been experimentally examined. The critical heat flux (CHF) could be enhanced to 3.7 MW/m2 which is three times of plain surface at most. The thicker the porous material prepared by electrodeposition, the CHF is enhanced. Moreover, the effect of the shape of HPP and the wickability on CHF were examined in this paper. Electrolytic deposition makes copper porous structure having porous part with pores about 10~20μm diameter and vapor escape channel which are 0.1~0.5mm in diameter. Vapor escape channels affecting wickability are formed by hydrogen bubbles generated during electrolytic deposition. Experimental results show that CHF increases with increasing wickability in thick porous plates as well as thin ones. In Addition, unlike the porous materials used to date, the CHF also continued to increase with increasing thickness, up to a sufficiently thick condition of 2 mm.</p>

DOI： 10.1299/jsmeicone.2023.30.1066

CiNii Research

Publisher：International Conference on Nuclear Engineering, Proceedings, ICONE  

Enhancement of pool boiling heat transfer using a copper honeycomb porous plate (HPP) made by electrolytic deposition has been experimentally examined. The critical heat flux (CHF) could be enhanced to 3.7 MW/m2 which is three times of plain surface at most. The thicker the porous material prepared by electrodeposition, the CHF is enhanced. Moreover, the effect of the shape of HPP and the wickability on CHF were examined in this paper. Electrolytic deposition makes copper porous structure having porous part with pores about 10~20µm diameter and vapor escape channel which are 0.1~0.5mm in diameter. Vapor escape channels affecting wickability are formed by hydrogen bubbles generated during electrolytic deposition. Experimental results show that CHF increases with increasing wickability in thick porous plates as well as thin ones. In Addition, unlike the porous materials used to date, the CHF also continued to increase with increasing thickness, up to a sufficiently thick condition of 2 mm.

Scopus

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

Spatial distribution of the heat transfer coefficient (HTC) in the vicinity of the wetting front is of crucial importance in predicting the wetting velocity during liquid film cooling of a high-temperature solid surface. However, mainly due to the lack of experimental data, no sufficiently reliable model has been developed so far for the HTC distribution in this fundamental thermal-hydraulic situation. In the present work, experiments using a high-speed infra-red camera were carried out to measure the transient of wall temperature distribution during wetting of a high-temperature vertical wall with a falling liquid film. Based on the HTC distributions calculated from the measured temperature data, dimensionless correlations were developed for the HTC distribution near the wetting front. It was confirmed that the propagation velocities of the wetting front (wetting velocity) calculated using the proposed correlations agree with the experimental data accumulated in this work well. (c) 2021 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2021.122422

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Repository Public URL： https://hdl.handle.net/2324/7178889

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Authorship：Lead author  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Superheated vapor is used in several industrial fields including sterilization, desiccation, and dehydrogenating. MCH (methylcyclohexane) has been vastly utilized as hydrogen carrier under several advantages. Superheated vaporization is necessary for catalytically dehydrogenating MCH. Current superheated vapor generation methods including high-frequency induction heating and microwave heating are difficult to obtain rapid generation and shutdown responses due to the large heat capacity of the fluid in the tank and the heater. For the realization of a carbon-free society and a hydrogen-based society, we proposed a method to generate superheated vapor using porous material with rapid response and high efficiency. Vapor may be generated rapidly from the surface of porous material due to small heat capacity of liquid in the meniscus. The main objective of the present research was to experimentally investigate the performance of the vapor generator using different working fluid with different property. As a result, fluid with low latent heat had better performance in generating superheated vapor rapidly and efficiently. Considering both heat conduction and fluid advection in porous material, the energy utilization efficiency and surface temperature were analyzed by a simplified one-dimensional model. The calculated results were shown to be in good agreement with the experimental results. The proposed vapor generator is suitable for superheated vaporization in MCH method from the analysis of the model.</p>

DOI： 10.1299/jsmeted.2022.59

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Heat pipe is a simple heat transfer device widely used in microelectronics cooling. It has a capillary structure called wick on its inner wall to convey condensate from a heat release section to a heated section. Nanoparticle layer is extremely thin and has strong capillary force. Hence, it could be used as the wick of heat pipes or vapor chambers to contribute downsizing them. Also, it is known that silica particles can be used to form a nanoparticle layer on the pipe inner wall as the wick of the heat pipe. It can achieve better heat transfer performance than the normal heat pipe containing a screen mesh in it. In this research, three types of nanoparticles were used to form the nanoparticles layer in heat pipe. It was explored experimentaly how the the heat transport performance depends on the nanparticles construting the wick.</p>

DOI： 10.1299/jsmepes.2022.26.b212

CiNii Research

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

DOI： 10.1088/1742-6596/2116/1/012002

Repository Public URL： https://hdl.handle.net/2324/7173500

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

DOI： 10.1115/ICONE28-61737

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

DOI： 10.1299/mej.20-00527

Repository Public URL： https://hdl.handle.net/2324/7178888

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

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

DOI： 10.1016/j.nucengdes.2020.110629

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