Numerical simulation of absorption-desorption cyclic processes for metal-hydrogen reactor with heat recovery using phase-change material

Highlights: • A metal hydride reactor equipped with a PCM was numerically investigated. • A model was developed to account for the equations of heat and mass transfer in PCM. • The liquid fraction in PCM was described by an approximation of Heaviside function. • The use of an unstructured CVFEM to discretize the governing equations. • The prediction of thermal coupling process between the hydride bed and the PCM domain. - Abstract: In this paper a transient two-dimensional mathematical model was developed for predicting the coupled heat and mass transfer within a metal-hydrogen reactor equipped with a phase change material (MHR-PCM for short). 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 unstructured control volume finite element method was used to discretize the governing equations and a computer code was developed on Fortran 90 to solve the obtained algebraic equations. The numerical model has been validated by comparison with experimental data and exploited to predict the thermal coupling process between the hydride bed and the PCM domain. The obtained numerical results revealed that the thermal energy stored by the PCM, when the metal-hydrogen reactor reaches 97% of its maximum capacity of hydrogen storage, can evacuate up to 80% of the hydrogen stored in the reactor.