Absorption and desorption of hydrogen in long metal hydride tank equipped with phase change material jacket

A numerical study was carried out to address the practical aspects of hydrogen absorption and desorption process in a long tubular LaNi5 metal hydride tank (MHT) integrated with Rubitherm phase change material (PCM) jacket for hydrogen supplying of PEM fuel cell. Different H2 supply pressures (p = 10, 15 and 20 bar), different discharge pressures (p = 1.5, 1.75 and 2 bar) and metal hydride bed porosities (0.4, 0.5 and 0.6) were rigorously analyzed to report their influences on transient and local temperature distributions across H2-MHT system and PCM jacket. The time-dependent changes of hydrogen to metal (H/M) ratio and PCM melt fraction were also investigated until they reach equilibrium. It was found that system temperature, PCM melt fraction and H/M ratio reach steady state with different rates, such that systems with higher supply pressure in absorption, lower discharge pressure in desorption and higher bed porosity approach steady state faster. Up to the steady state, 64%, 79% and 91% of the initial volume of solid PCM liquefies in absorption and 67%, 83% and 95% of liquid PCM solidifies in desorption for bed porosities of 0.6, 0.5 and 0.4, respectively. The MHT is charged with hydrogen much faster under high supply pressures. Also, it is discharged much faster under lower discharge pressure. Inserting metal foam in the PCM jacket enhances the thermal conductivity, and significantly reduces the charging and discharging time.