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

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


Presentations
1. Yasuyuki Takata, Thermal Problems of Hydrogen at High Pressures, Asian Thermophysical Properties Conference(ATPC2019), 2019.10, Hydrogen is a promising energy career in the future carbon-neutral society. In December 2014, Toyota motors has started to sell a commercial fuel cell vehicle (FCV) into Japanese market and has been increasing its production year by year. In order to disseminate the FCVs, the hydrogen refueling station (HRS) should be placed everywhere in the society. There are about 90 HRSs in Japan as of January 2019.
The current FCV has 5kg of hydrogen at 82MPa in tank pressure. Therefore, the HRS has to handle hydrogen with higher pressure up to 100MPa to refill it to FCVs. Currently, the charging time to fill up the H2 tank is expected to be 3 min or shorter. However, such a rapid refueling process causes temperature rise in the H2 tank by adiabatic compression. The limit temperature of the H2 tank is 85C because of the melting point of a bonding agent for carbon fibers of the tank. To avoid undesirable temperature rise, the recent HRSs are equipped with a precooling device that cools the hydrogen down to -40C in advance. However, this precooling process causes the other problems. One is the overcharge of hydrogen.
Since the hydrogen gas at low temperature is injected into tank up to target pressure at the end of refueling process, the tank pressure increases gradually due to heat transfer from the surrounding. This pressure rise by heat transfer sometimes exceeds the limit pressure of the tank. The second problem is a frost formation around the injection nozzle and the receptacle. Sometimes, ice is formed and the hydrogen nozzle is stuck to the receptacle. For safety operations of HRS, these thermal problems must be solved.
Our research effort is devoted to the first problem. To ensure the safety of FCVs during refueling hydrogen, transient pressure and temperature in tank should be predicted with sufficient accuracy. The first step is to collect accurate thermophysical property data for hydrogen in a wide range of pressures and temperatures. We have been measuring thermodynamic and transport properties of hydrogen up to 100MPa and 500C to develop a reliable database. Based on this hydrogen thermopysical proerty database, we have been developing a useful software for dynamic simulation of HRS which predicts flow rate, temperatures and pressures of HRS and H2 tank of FCV. Some typical thermo-technical problems with hydrogen refueling process are introduced in the presentation..
2. Yasuyuki Takata, Biao Shen, Sumitomo Hidaka, Koji Takahashi, The Role of Hydrophobicity on Early Onset and Enhancement of Nucleate Boiling, 6th Nano and Micro Flows Conference, 2018.09, Wettability effect is one of the key parameters that influences boiling characteristics. The present study reveals the role of hydrophobicity in relation to the effect of dissolved air in liquid water. The hydrophobicity works as an excellent nucleation site and, therefore, by making use of biphilic surface the nucleate boiling is significantly enhanced. The boiling performance of biphilic surface is of about 6 times larger than that of mirror copper surface in subatmospheric condition. The effect of dissolved air on the onset of nucleate boiling (ONB) has been made clear by making use of a special experimental apparatus that can remove air from boiling water. It was found that the dissolved air assists early onset of boiling and enhances boiling performance..
3. Yasuyuki Takata, Pool Boiling on Superhydrophilic/phobic Surfaces, UK Heat Transfer Conference, 2015.09.