CFD simulation of heat and mass transfer processes in a metal hydride hydrogen storage system, taking into account changes in the bed structure

International Journal of Hydrogen Energy. 2024.

Minko K., Lototskyy M., Bessarabskaya I., Boris P. Tarasov

CFD modelling of heat-and-mass transfer in metal hydride (MH) beds is an important step in the development
and optimisation of MH reactors for hydrogen storage, compression and separation/purification. In the existing
models, the mass conservation equation includes the density of solid in the non-hydrogenated (ρs) and hydrogensaturated (ρss) states. To provide constant porosity of the MH bed during H2 absorption/desorption, assumption ρs<ρss is typically taken. However, this assumption contradicts to well-known fact that hydrogenation of hydrideforming alloys is accompanied by the expansion of crystal lattice of the metallic matrix and, therefore, by the
decrease of the solid density by 15–25%. This work presents results of the modelling which takes this effect into account. The model assumes that the density of the MH changes linearly as the starting hydride-forming alloy is saturated with hydrogen, while the volume of the MH bed remains constant. The last assumption is a limiting estimation because it provides the maximum possible reduction in the porosity during H2 absorption process.
The model was validated using published experimental data on a cylindrical MH reactor filled with 422 g of
LaNi5. It was shown that accounting the realistic changes in the MH density can significantly affect the simulation
results.

Keywords: modelling, Hydrogen storage, Bed structure, Heat and mass transfer, Metal hydride