Numerical simulation of metal hydride hydrogen storage device with pin fin tube heat exchanger

Absorption of hydrogen gas into a metal hydride is an exothermic process. Heat released during the reaction must be extracted from the metal hydride hydrogen storage device to enhance the absorption rate of hydrogen. Previous studies suggest that insertion of an effective heat exchanger inside the storage device improves the absorption rate of hydrogen. In our present study, six different pin fin tube heat exchanger designs are proposed. Individual charging time of designed heat exchangers is found out numerically and a comparative study is carried out among all of them. COMSOL Multiphysics 4.3b is used for designing and simulating the models. Among the proposed designs, a final design is selected based on the least charging time and detailed 3-D mathematical model is developed for further study of absorption process inside the storage device. Influence of the hydrogen supply pressure on the charging time of the storage device has been examined. It is found that higher supply pressure of hydrogen gas reduces the charging time of the storage device. Variation of bed temperature and concentration along the axial distance of the storage device has also been investigated. It is found that mid part of the device is having constant temperature as well as concentration profile at any time interval while parts near the flange portions saturate earlier than middle region. The absorption process takes 727 s to absorb 1.4 wt% of hydrogen at the operating conditions of 15 bar, 298 K and 0.113 Kg/s. This numerical study suggests that the good selection of heat exchanger geometry is important for rapid absorption process inside the storage device.