Performance simulation of metal hydride based flat coupled beds with differential sizes for cooling/heating

Hydrogen being the most abundant element in the universe has great potential towards decarbonisation at the point of usage. Metal hydride-based heat pumps/ refrigerators are getting increasing acceptance due to its environment friendliness and safety. These systems operate over a wide range of temperatures and pressures. The thermal performance of these systems depends mainly on the reaction kinetics of the alloy pairs. Difference in the reaction rates of the alloy pairs, causes a certain amount of hydride to go unutilized during cycling. While a variety of reactor designs and heat transfer enhancements are suggested, optimal thermal design of coupled beds with minimum weight and cycle time remains a major challenge. In the present study, numerical simulation of differently sized coupled beds based on the alloy pair of LaNi4.7Al0.3 - La0.8Ce0.2Ni5 is carried out using COMSOL Multiphysics® commercial code. The effect of mass ratio on the hydrogen pressure and hydride concentration in the coupled bed is highly significant. It is found that 12 % increase in COP (0.28) is obtained for a cycle time of 260 s and mass ratio of 1.5. This corresponds to minimum alloy weight ensuring effective transfer of hydrogen across HT-LT reactors.