Multi-step numerical method for the hydrogen storage performance optimisation of metal hydride reactors

Metal hydrides are expected to play a vital role in large-scale hydrogen storage and transportation. Efficient thermal management of the reaction heat during hydrogen charging plays a key role in improving the performance of charging hydrogen. In this study, a multi-step numerical method was proposed to optimise the hydrogen storage performance of metal hydride reactors. Four typical reactors based on the cooling mode, heat-transfer structure, and thermal conductivity regulation of metal hydride beds were designed according to national standards. The four reactors included an air-cooled reactor with metal foam, a jacketed water-cooled reactor with metal foam, a tube-bundle water-cooled reactor, and a tube-bundle water-cooled reactor with metal foam. First, three-dimensional numerical models were established considering the thermal effects of hydrogen absorption. The comprehensive hydrogen storage performances (CHSPs), including the hydrogen charging rate, metal hydride bed volume, and mass density, were compared and analyzed. The bundled water-cooled reactor with metal foam had the highest CHSP at all inlet pressures and was considered the primitive reference structure. Subsequently, the parameter sensitivity was investigated for the metal foam porosity, volume ratio, and number of heat exchanger tubes. The turning point corresponding to the best CHSP value was determined for each parameter. Finally, the Taguchi method was adopted to obtain the optimised parameter combination, in which the metal foam porosity, volume ratio, and the number of heat exchanger tubes were 0.92, 0.15, and 101, respectively. The final CHSP was improved by 2.05 times compared with that of the reference reactor. The proposed hydrogen storage reactor design and optimisation route can provide helpful guidance for the development and design of industrial hydrogen storage reactors.