The storage performance of metal hydride hydrogen storage tanks with reaction heat recovery by phase change materials

Abstract

The hydrogen storage of metal hydrides (MHs) is an exothermic process. The reaction enthalpy of magnesium hydride is 75 kJ/mol. Phase change materials (PCM) can be integrated with a MH hydrogen storage tank (MHST) to recycle the absorption heat as the heat source for desorption. To improve the heat transfer and hydrogen storage performance, this work comparatively studied the various configurations of the PCM based MHST. A numerical model is built to trace the transfer and storage process for two MHSTs with the PCM surrounded layout and sandwiched MH-PCM units. The results show that the configuration methods of PCM affects the hydrogen storage performance. The sandwiched MH-PCM units has faster heat transfer and reaction rate for the larger heat transfer area and smaller thermal resistance. The amount of PCM affects the reaction fraction due to the heat storage capacity. For the MHST with sandwiched MH-PCM units, when the amount of PCM is sufficient, the reduction of PCM will slightly decrease the average absorption rate and increase the average desorption rate by 21.8%. Considering the weight of PCM, the quantitative relationship is established among the mass ratio of PCM to MH, the maximum conversion rate of MgH2 and the actual gravimetric hydrogen storage capacity. When the amount of PCM is just sufficient, there is a maximum gravimetric hydrogen storage capacity of 0.733 wt%.