Models for metal hydride particle shape, packing, and heat transfer

A multiphysics modeling approach for heat conduction in metal hydride powders is presented, including particle shape distribution, size distribution, granular packing structure, and effective thermal conductivity. A statistical geometric model is presented that replicates features of particle size and shape distributions observed experimentally that result from cyclic hydride decrepitation. The quasi-static dense packing of a sample set of these particles is simulated via energy-based structural optimization methods. These particles jam (i.e., solidify) at a density (solid volume fraction) of 0.671 ± 0.009 – higher than prior experimental estimates. Effective thermal conductivity of the jammed system is simulated and found to follow the behavior predicted by granular effective medium theory. Finally, a theory is presented that links the properties of bi-porous cohesive powders to the present systems based on recent experimental observations of jammed packings of fine powder. This theory produces quantitative experimental agreement with metal hydride powders of various compositions.

► Fragmented hydride size distributions agree with Poisson plane field predictions.
► Jammed packings of non-cohesive hydride-like particles are denser than experimental powders.
► Heat does not percolate through the solid phase in hydride-like packings.
►  A transport theory of cohesive-driven bi-porous structures matches experimental conductivities.
► Engineering strategies that seek to enhance conductivity should aim to increase packing density.