Optimal design of disc mini-channel metal hydride reactor with high hydrogen storage efficiency

Abstract

Metal hydride is one of highly efficient methods to storage H2 with the high density and mild operating conditions. As a reaction place for metal hydride, the reactor should have excellent heat transfer characteristics to deal with the strong thermal effect generated by the reaction. Novel disc mini-channel reactors without and with jacket (DMCR and DMCR-J) were proposed to improve the H2 storage efficiency greatly by increasing the uniformity of temperature distribution inside reactor. The reaction performances were investigated and optimized by 3D COMSOL models, and the results indicated the optimal performances of both reactors could be achieved when the heat transfer layer height was 0.9 mm and the metal hydride layer height was 5 mm, corresponding to the optimal H2 storage amount per unit height was 0.17 g mm−1. Meanwhile, optimal operating conditions of both reactors were H2 pressure of 1 MPa for absorption and 0.1 MPa for desorption, heat exchange fluid temperature of 293 K for absorption and 353 K for desorption, flow velocity of 3 m s−1 and metal hydride filling fraction of 0.7. Moreover, heat transfer jacket and reactor shape had little influence on the reaction performance. In addition, the five reactors with or without jacket were systematically investigated and compared, revealing the outstanding heat transfer and reaction performances of DMCR and DMCR-J, which only needed about 300 s for absorption and 200 s for desorption to reach 99.7% of maximal H2 storage capacity for 1.56 kg metal hydride, saving more than 80% reaction time compared with the straight tube reactor.