HEAT AND MASS-TRANSFER IN METAL HYDRIDE BEDS FOR HEAT-PUMP APPLICATIONS

Heat and mass transfer in a metal hydride bed is modeled. The mode includes heat conduction, hydrogen flow governed by Darcy's law modified for the transitional flow regime, and sorption kinetics assuming that diffusion across the hydride is the rate limiting step. The model parameters are established for LaNi4.7Al0.3 alloy using available experimental data. Parametric calculations for a space vehicle heat pump application show the competing effects of heat transfer, hydrogen flow and sorption kinetics limitations. The effect of augmenting heat conduction is demonstrated. Optimum bed thicknesses appear limitations. The effect of augmenting heat conduction is demonstrated. Optimum bed thicknesses appear to be in the range 10-20 mm for a 3 min absorption time and kb = 1.3 ∼ 5 W m-1 K-1. © 1990.