Analysis of Heat and Mass Transfer During Charging and Discharging in a Metal Hydride - Phase Change Material Reactor

Abstract

This paper presents the heat and mass transfer study during charging and discharging processes in a metal hydride reactor (MHR) equipped with phase change material (PCM). The PCM numerical model is newly developed and incorporated into the metal hydride (MH) model, which was presented earlier [1]. It is based on the enthalpy-porosity formulation and considers source/sink terms in energy and momentum conservation equations. The study explores the effects of metal foam incorporated into PCM, and the variation of its porosity and pore density towards better heat transfer, and hydrogen charging and discharging rates. Detailed performance analysis of the MHR-PCM system with and without metal foam is performed, and the results show a significant improvement in performance with the PCM having metal foam embedded in it. The study on the effect of metal foam porosity reveals an interplay between effective PCM thermal conductivity and PCM amount on the hydrogen charging rate. The study clearly illustrates the limitation posed by the MH powder thermal conductivity on heat transfer and optimizes the metal foam morphology for improved hydrogen charging and discharging rates. The natural heat convection in the PCM is found to be negligible due to its high density. A brief study on the influence of hydrogen inlet and exit pressures, and the amount of PCM on charging and discharging rates is also performed. The study provides an in-depth insight into the formation of liquid and mass fraction fronts in the PCM and MH regions, respectively, under different operating conditions and PCM configurations.