Optimal analysis of the exothermic process of a Mg/MgH2 thermochemical heat storage system

A two-dimensional transient mathematical model was established for a magnesium/ magnesium hydride thermochemical heat storage system. The heat and mass transfer phenomena of the exothermic process of the system were simulated and the influences of wall temperature and bed effective thermal conductivity on the reaction rate were investigated. The results show that, during the exothermic process, there is an optimal wall temperature that gives the fastest reaction rate, both higher and lower wall temperatures make the bed temperature deviate from the theoretical optimal value, thereby decreasing the reaction rate. It is shown that the optimal wall temperature depends on the effective thermal conductivity. It is not always that the higher the effective thermal conductivity of the bed, the better the reaction rate. A number of factors including the specific wall temperature and hydrogen pressure have to be considered when making a choice of the effective thermal conductivity.