(151e) Optimization of Metal Hydride Based Hydrogen Storage Bed Designs

Design of metal hydride storage bed is a key factor that influences the storage capacity, gravimetric hydrogen storage density, and refueling time for automotive on-board hydrogen storage systems. The choice of storage bed design incorporating the heat exchanger, and corresponding design parameters is not obvious. A systematic study is presented to optimize the bed heat exchanger design using CFD modeling. Three different shell and tube heat exchanger designs are chosen. In the first design, metal hydride is present in the shell and heat transfer fluid flows through straight parallel cooling tubes placed inside the bed. The cooling tubes are interconnected by conducting fins. In the second design, the heat transfer fluid flows through helical tubes in the bed. The helical tube design permits use of a specific maximum distance between the metal hydride and coolant for removing heat during refueling. In the third design, the metal hydride is present in the tubes and the fluid flows through the shell. An automated tool is generated using COMSOL-MATLAB integration to arrive at the optimal geometric parameters for each design type. Using sodium alanate as the reference storage material, relative merits and demerits of each design type are analyzed in detail and a comparison of the gravimetric and volumetric hydrogen storage densities for the three designs is presented.