Numerical Simulation of Metal Hydride Hydrogen Storage Device with Pin Fin Tube Heat Exchanger

Abstract

-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.

State of the Art in Development of Heat Exchanger Geometry Optimization and Different Storage Bed Designs of a Metal Hydride Reactor

“…Complex heat exchanger designs, such as those proposed by Keshari V. and Maiya M. P. [ 213 ], can be produced using 3D printing technology with high efficiency and accuracy ( Figure 36 ). Moreover, straight and helical copper tubes can also be manufactured via 3D printer [ 214 ].…”

Measurement of effective thermal conductivity of LaNi$_5$ powder packed bed

“…However, as metal-hydride alloy split into fine powders by mechanical constraints generated by lattice volume expansion during hydriding-dehydriding cycles, the effective thermal conductivity of the metal-hydride packed bed decreases drastically [6]. Therefore, various thermal designs for enhancing the heat transfer performance of storage systems have been developed over the past several decades [7][8][9]. Since thermal designs involving metal fins or foams take up internal space of the storage system and eventually reduce the system energy density, accurate measurement of the effective thermal conductivity of metal-hydrides is crucial.…”