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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Heat and Mass Transfer  

Since water electrolysis is a pollution-free and economical method to produce hydrogen which has a great potential as an energy carrier, it is imperative to improve the performance of water electrolysis for efficient hydrogen production. Supposing that the analogy between boiling and water electrolysis holds, the next interesting question is whether the water electrolysis performance can also be significantly improved by using a method that improves the heat transfer coefficient and the critical heat flux (CHF). The critical current density (CCD), which is the upper operation limit of water electrolysis, is considered to be one of the keys for effective hydrogen generation. However, the study on the enhancement of CCD has rarely been conducted. It is known that the boiling CHF can be improved by a honeycomb porous plate (HPP) due to two effects, capillary force and path separation of gas-liquid. In this work, we applied a cooling method using an HPP which has succeeded in improving the boiling CHF to alkaline water electrolysis. For the first time, we have succeeded in improving the CCD to approximately 1.3 times (CCD: 6.6 A/cm2) compared to without capillary force case (CCD: 5.1 A/cm2). As regards the mechanism, the effect of the liquid supply by capillary action and the improvement of the bubble discharge by separating the gas–liquid flow path using the honeycomb structure of the HPP play an important role in increasing the CCD.

DOI： 10.1016/j.ijheatmasstransfer.2023.124420

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リポジトリ公開URL： https://hdl.handle.net/2324/7178892

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Heat and Mass Transfer  

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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リポジトリ公開URL： https://hdl.handle.net/2324/7178891

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Thermal Engineering  

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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リポジトリ公開URL： https://hdl.handle.net/2324/7178893

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmepes.2023.27.b122

CiNii Research

記述言語：英語   出版者・発行元：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

出版者・発行元：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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Heat and Mass Transfer  

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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リポジトリ公開URL： https://hdl.handle.net/2324/7178889

記述言語：その他  

担当区分：筆頭著者  

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmeted.2022.59

CiNii Research

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmepes.2022.26.b212

CiNii Research

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

DOI： 10.1088/1742-6596/2116/1/012002

リポジトリ公開URL： https://hdl.handle.net/2324/7173500

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

DOI： 10.1115/ICONE28-61737

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1299/mej.20-00527

リポジトリ公開URL： https://hdl.handle.net/2324/7178888

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nucengdes.2020.110629

記述言語：日本語   掲載種別：研究論文（学術雑誌）