Measurement and theoretical analysis of effective thermal conductivity of lanthanum pentanickel powder beds for hydrogen storage in different particle sizes and bed porosities

Abstract

Particle diameter and bed porosity change due to the expansion and contraction of metal hydride particles during hydrogen absorption and desorption, which leads to variations in the effective thermal conductivity of metal hydride beds. Therefore, the effective thermal conductivity of the metal hydride beds under different bed porosities and particle diameter must be measured for the design of metal hydride-based hydrogen storage tanks. In this study, the effective thermal conductivities of four kinds of lanthanum pentanickel (LaNi5) powder beds with different bed porosities and particle diameters were measured in various gas atmospheres with gas pressure varying from 0.1 to 4.0 MPa. The volume mean diameters of the four kinds of LaNi5 powders equal 335.2, 196.4, 147.7, and 23.7 μm, respectively. Subsequently, the effects of bed porosity and particle diameter on the effective thermal conductivities were analyzed through the modified Zehner–Schlünder–Damköhler model considering the Smoluchowski effect. Experimental results show that particle diameter and bed porosity influence markedly the effective thermal conductivity of lanthanum pentanickel (LaNi5) powder beds. However, the findings of theoretical analysis based on the modified Zehner–Schlünder–Damköhler model reveal the considerably weaker effect of particle diameter on the effective thermal conductivity under identical bed porosity compared with the measurement results. Such a finding was observed because the variation in particle diameter inevitably changed bed porosity during the effective thermal conductivity measurement, which also affected the effective thermal conductivity of the beds. In addition, decreasing bed porosity and increasing particle diameter can remarkably improve the heat transport via the gas–solid mixture pathway, which improved the effective thermal conductivity of the beds and thus explained the experimental results.