Influence of geometrical non-uniformities of LaNi5 metal hydride bed on its structure and heat and mass transfer at hydrogen absorption

We perform cycling of a 500 g bed of La_0.9Ce_0.1Ni₅ intermetallic compound in vertical and horizontal orientations with measurements of PCT isotherms, and further XRD and SEM investigation of bed structure. Significant decrease in equilibrium absorption pressure is observed in vertical orientation of the bed from 1.58 to 1.36 MPa at 333K, and from 2.68 to 2.51 MPa at 353K, accompanied by evident particle segregation by the bed height and densification at a bottom with formation of a robust agglomerate of small particles (< 10 μm) jointed with big particles of the size 100-200 μm, while particle size distribution in upper parts is more uniform with mean size about 10-20 μm. Fill density increases by 15% from the top to the bottom from 3.26 g/cm³ to 3.86 g/cm³ while structural properties of particles remain the same with X-ray density 8.31 g/cm³. Investigations of heat and mass transfer inside a vertical metal hydride reactor RSP-8 with 1 kg of La_0.9Ce_0.1Ni₅ also show considerable non-uniformity of pressure inside the bed. If the reactor is charged from the top the hydrogen pressure at the bottom is lower on 0.2-0.3 MPa, which results in earlier occurrence of heat and mass transfer crisis. (paper)