Performance improvement of a U-tube heat exchanger based hydrogen storage reactor by phase change materials

Solid-state hydrogen storage technology using metal hydrides as carriers has great application prospects. This study aims to optimize the heat transfer resistance and absorption kinetics issues encountered in practical applications of LaNi5-H2 storage materials in storage reactors. A mathematical model for the hydrogen absorption process in the reactors based on U-tube and straight-tube heat exchangers was built, and the advantages of U-tube structure and the flow characteristics of the heat transfer fluid on its heat transfer and absorption performance were analyzed. To further enhance the U-tube based reactor's performance, phase change materials (PCM) were subsequently introduced as an auxiliary heat transfer medium, while the amount of PCM and the thermal conductivity of the reaction bed were optimized. The results showed that the appropriate PCM dosage could overcome the inherent defects of the U-tube heat exchanger and significantly improve heat dissipation and reaction rates of the reactor, and the H2 absorption completion time was shortened by 1.4 times. In addition, the increased thermal conductivity of reaction beds is equally important for the enhancement of heat transfer and absorption rate. Nevertheless, further increase of PCM's thermal conductivity has a limited effect on the improvement of the performance.