Integration of hydrogen storage and heat storage in thermochemical reactors enhanced with optimized topological structures: Charging process

Abstract

The low density for hydrogen storage can be solved by metal hydrides, and the energy loss for hydrogen storage with metal hydrides can be recovered by the combination of metal hydrides (Mg/MgH2) with thermochemical heat storage materials (MgO/Mg(OH)2) under the different reaction temperatures. However, the poor heat conduction of thermochemical materials limits the heat transfer rate and the implementation of this technology. In this study, an accurate theoretical model of hydrogen charging process in the hydrogen storage reactor assisted with heat storage was developed to accommodate the operating pressure. A novel method to overcome the poor heat transfer problem was proposed by topology optimization of high thermal conductivity fins for matching the heat transfer and reaction rate in the hydrogen storage side with those in the heat storage side. Increasing the average temperature of MgO/Mg(OH)2 was considered for the formulation of the topology optimization problem, and a density-based approach was used. The influence of the conductivity of materials on the topology optimization was discussed. The outcomes displayed that higher thermal conductivity accommodated more heat transfer directions, resulting in a distinct branch structure. Furthermore, the obtained topologies were geometrically reconstructed and evaluated during the hydrogen charging process. Results revealed that the topology optimized geometry had outstanding heat transfer performance, with an obvious improvement in terms of hydrogen charging time over the reactor without fins. This work can provide the theoretical basis for thermochemical conversion processes of hydrogen storage and heat storage, the implementation procedure for topology optimization, and the design guidance of thermochemical reactors for hydrogen storage assisted with heat storage.