Effect of heat transfer enhancement on the performance of metal hydride based hydrogen compressor

Abstract

A single stage metal hydride based hydrogen compressor has been developed using La0.8Ce0.2Ni5 hydride. The performance of the hydrogen compressor was evaluated in three different configurations to determine the effect of heat transfer augmentation. Two different types of metal hydride pellets were developed. Graphite flakes were mixed with La0.8Ce0.2Ni5 hydride for the first type of pellets. While in the second type, an augmentation structure made with copper wire mesh was embedded with the mixture of La0.8Ce0.2Ni5 hydride and graphite flakes. All the three types of La0.8Ce0.2Ni5 hydride beds namely, with loose MH powder (LMHP), pellets of MH powder and graphite fibres (PMHGF), and pellets of MH, graphite fibres with embedded copper wire mesh structure (PMHGFCu) were tested for a wide range of pressure and temperature conditions and their performances were compared. As expected, the heat transfer enhancement of La0.8Ce0.2Ni5 hydride bed resulted in enhancement of kinetics of hydrogenation/dehydrogenation and performance of hydrogen compressor. The maximum pressure ratio, maximum cycle efficiency, minimum time to reach saturation stage during absorption in cases of LMHP/PMHGF/PMHGFCu were 4.18/5.04/5.2, 5.1%/5.94%/6.07%, 400 s/250 s/220 s respectively. The highest increase in compression ratio and efficiency in case of pellets bed compared to those for powder bed were 76.51% and 29.3% respectively.