Effect of thermal conductivity of the phase change material (PCM) on the absorption process of a metal-hydrogen reactor (LaNi5-H2)

Abstract

In order to make the storage mode in a metal-hydrogen reactor (LaNi5-H2) more cost competitive in terms of thermal energy, we propose in this study to store the released heat during hydrogen absorption (exothermic) by using a phase change material (PCM), for recovering it during desorption process. A transient two-dimensional mathematical model to predict the heat and mass transfer in the hydride bed and the phase change medium is presented and solved numerically by the unstructured control volume finite element method (CVFEM). For this model, the liquid fraction in the PCM was described by an analytic approximation of the Heaviside step function which, to the knowledge of the authors, is applied for the first time to study phase change problems. The validation of the numerical model has been performed by comparison with experimental data, and several numerical simulations were carried out to evaluate the effect of the thermal conductivity of PCM on the dynamic behavior of hydriding and the melting processes.