Abstract:To study the heat and mass transfer characteristics of hydrogen desorption process in metal hydride hydrogen storage reactor, a two-dimensional axisymmetric mathematical model for metal hydride reactor was established. The reactor was filled with composite compacts made of Ti_0.95Zr_0.05Mn_1.55V_0.45Fe_0.09 alloy and expanded natural graphite. The validity of the model was verified by the experimental data in literature. The effects of heat transfer fluid temperature, mean fluid velocity and hydrogen delivery pressure on the hydrogen desorption process were investigated, and the hydrogen desorption characteristics were compared at the optimal and baseline sets of the operating parameters. The kinetics characteristics of the hydrogen desorption reaction were analyzed at the optimal sets of the operating parameters. The simulation results showed that the heat transfer performance is better near the heat exchanger tube wall, where the hydrogen desorption reaction proceeds more quickly. When the temperature increases from 313.15 K to 353.15 K, the hydrogen desorption time decreases from 17100 s to 6700 s. Increasing the mean velocity can accelerate the hydrogen desorption process, but its strengthening effect is limited. When the flow rate of heat transfer fluid exceeds 3 m/s, the enhancement effect of increasing the mean fluid velocity is not obvious due to the contact thermal resistance between the metal hydride bed and the wall of the heat transfer tube becomes the main thermal resistance in the overall heat transfer process. The optimal operating parameters are as follows as: the hydrogen delivery pressure of 0.3 MPa, the temperature of heat transfer fluid of 353.15 K, and the mean velocity of heat transfer fluid of 3 m/s. Compared with the baseline set of the operating parameters, the hydrogen desorption reaction time is shorten by about 56%, and hence the optimization of the operating parameters can significantly improve the dehydrogenation rate of the reactor. The hydrogen desorption process of the Ti_0.95Zr_0.05Mn_1.55V_0.45Fe_0.09 alloy is mainly controlled by hydrogen pressure only in the first 4 s, while the whole reaction process is mainly controlled by the heat transfer process.