Hydrogen storage systems based on metal hydrides with efficient heat removal

Wang, Hui
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University of Delaware
The overall objective of this research was to accelerate the rate at which hydrogen gas can be charged into a hydride-based hydrogen storage tank. During the charging process, the absorption reaction of hydrogen gas into a metal hydride bed is exothermic. The temperature of the system will increase if the heat released is not removed quickly from the system and reduce the absorption rate. Hence, the rate of hydrogen storage into a tank containing metal hydride materials strongly depends on the heat removal rate from the hydrogen storage system. To increase the heat removal rate the following four approaches were explored: (i) Enhancement of the thermal conductivity of the metal hydride bed by incorporating conductivity-enhancing materials such as aluminum (Al) foam. (ii) The use of genetic algorithms to optimize the parameters and placement of spiral coil heat exchangers with fins. (iii) Introduction of an active cooling environment by embedding a helical coil heat exchanger into the hydrogen storage tank. (iv) Use of a physical mixing method to improve the heat removal rate. In order to investigate the effectiveness and the role of various factors in the above proposed approaches, we developed a numerical model that incorporates flow, reaction kinetics and heat transfer within the software package ANSYS. Simulations were used to explore various storage tank designs containing hydride materials and various cooling enhancement methods to find the optimal materials and design for accelerating the charging rate of the hydrogen into the tank. An experimental setup was also designed and fabricated to charge the hydrogen into a hydride-based storage tank. The temperature and pressure of the tank was monitored during charging to validate the simulations.