Performance improvement of adsorptive hydrogen storage on activated carbon: Effects of phase change material and inconstant mass flow rate

Due to the multiple advantages of activated carbon (e.g. high specific surface area, safety and low cost) toward hydrogen storage, the subject of heat management in H-2-storage tanks has become a research focus in recent years. In this work, using a computational fluid dynamics (CFD) model (implemented in Fluent software), the performance of a hydrogen storage tank (packed with activated carbon) was analyzed in the presence of PCM/oil-based thermal recovery/release systems. The charging, dormancy, and discharging cycles of the storage tank were investigated with respect to the variation of the injected mass flow rate of hydrogen (from 2 x 10(-4) to 8 x 10(-4) kg/s). There was good agreement between our findings and those obtained from the experiment. It was observed that the adsorption capacity of the solid bed is proportionally enhanced with the rise in the mass flow rate of hydrogen. In addition, independently of the used hydrogen mass flow rate, it has been observed that the charging periods were ended at the same instant (i.e. t = 400 s). According to the enthalpy contours and liquid fraction of PCM (similar to 18 and 30 % at 400 and 4000 s, respectively), it has been concluded that the thermal conductivities of the adopted PCM and that of solid bed (activated carbon) should be enhanced for better performance of the hydrogen stocking tank. Finally, from a viewpoint of storage performance and process cost, it is therefore possible to realize rapid charging/discharging of the activated carbon tank with adopting a PCM and oil-based thermal unit for heat management.