Prediction of hydrogen desorption performance of Mg₂Ni hydride reactors

This work performs the simulation of hydrogen desorption processes with Mg₂Ni hydrogen storage alloy to investigate the canister designs. Reaction rates and equilibrium pressures of Mg₂Ni alloy were calculated by fitting experimental data in literature using least squares regression. The obtained reaction kinetics was used to model the thermalfluid behavior of hydrogen desorption. Since the alloy powders will expand and shrink during the absorption and desorption cycle, the canisters considered are comprised of expansion volume atop the metal bed. In order to enhance the heat transfer performance of the canister, an air pipe is equipped at the canister centre line with/without internal fins. Detailed equations that describe the force convection of the heat exchange pipe and the natural convection at the reactor wall are carefully incorporated in the model. Simulation results show that the bare cylindrical canister can not complete the desorption process in 2.8 h, while the canister equipped with the concentric heat exchanger pipe and fins can complete desorption within 1.7 h.Results also demonstrate that the reaction rates can be further increased by increasing the pipe flow velocity and/or increasing the fin volume.