Performance investigation and optimization of metal hydride reactors for high temperature thermochemical heat storage

• Effects of certain heat transfer enhancement measures were evaluated.
• The reaction is accelerated when the heat transfer enhancement measures are adopted.
• A reduction by 50% is attained by other four reactors in comparison to the reactor A.
• There is an increase of 1.2 K in the maximum outlet temperature of fluid using the measures.
• Metal hydride compacts are recommended in metal hydride based heat storage systems.

The metal hydride based thermal energy storage (MHTES) technology is expected to be an attractive option. Being a key component, the metal hydride reactor should facilitate good heat and mass transfer. In this study, the effects of two heat transfer enhancement measures, i.e. using metal fins and making metal hydride powder into compacts, on the MHTES system performance were evaluated. The heat and mass transfer characteristics in five different reactors using different enhancement measures were compared. As shown in the simulation results, the temperature distributions of the reactors are more uniform when the bed thermal conductivity of the reactors is increased by making metal hydride powder into compacts. Moreover, the average reaction rate is remarkably increased when the measures for heat transfer enhancement are adopted. When the gravimetric heat storage rate (GHSR) is used as a comprehensive evaluation index, the optimum reactor of the MHTES system is not equipped with using any fins but using metal hydride compact technique. Therefore, metal hydride compact technique is recommended in the MHTES applications while expensive metal fins can be removed.