Simulation studies on heat and mass transfer in high-temperature magnesium hydride reactors

摘要

Magnesium hydride is one of the most promising materials for hydrogen storage and high-temperature heat storage. The heat and mass transfer processes occurring in magnesium hydride reactors are very complicated. In the present study, a mathematical model for a magnesium hydride reactor is developed to investigate the mass and heat transfer characteristics under various operating conditions. The distributions of gas velocity, gas pressure, temperature and reacted fraction are obtained by solving the rigorous model. Two versions of the model, which are respectively applied on two different computational domains, are investigated. The simplified version of the model is proved capable of predicting the performance of the magnesium hydride reactor, with high computation efficiency and acceptable accuracy. The simulation results indicate that an increase in hydrogen supply pressure (p_(in)) accelerates the absorption process due to enhanced absorption reaction kinetics. The hydriding time decreases when heat transfer fluid (HTF) velocity (u_f) goes up, because the convection heat transfer coefficient between HTF and the magnesium hydride rises with increasing HTF inlet velocity. Moreover, an increase in HTF inlet temperature (T_(in)) leads to an increase in the equilibrium pressure of the magnesium hydride which decelerates the hydrogen absorption reaction. The optimal setting of the three operating parameters for the magnesium hydride reactor is determined based on the mathematical model, and the corresponding values of the parameters are as follows: p_(in) = 2.6 MPa, T_(in) = 473 K and u_f = 5 m s~(-1).