Heat supply to and hydrogen desorption from magnesium hydride in a thermally insulated container with hot gas flow

Abstract

We experimentally studied hydrogen desorption from MgH2 by supplying heat via a hot gas flow. Porous sheets of MgH2 held in a sponge-like carbon nanotube (CNT) matrix were developed and placed in a coaxial double-tube reactor. Ar gas was heated using a cylindrical heater and then flowed alongside the MgH2-CNT sheets, thereby increasing the temperature of the sheets and enabling the desorption of hydrogen into the gas flow. The total energy efficiency was approximately 6.2% when 64% of hydrogen in MgH2 was desorbed. A numerical simulation was conducted for the heat transfer and hydrogen desorption, and the obtained results were consistent with the experimental results. According to the simulation, the low energy efficiency was attributed to the small heat capacity ratio of MgH2 to the reactor (0.082) and considerable radiative heat loss (53%). The simulation was used to predict energy efficiency improvements, and the efficiency was considered to increase to 12% upon increasing the heat capacity ratio from 0.082 to 1.4, and further to 21% upon doubling the Ar flow rate, which enhanced the convective heat transfer from the heater to MgH2.