Experimental and numerical study of a magnesium hydride tank

A small-scale experimental magnesium hydride tank was designed and tested to illustrate the feasibility of hydrogen storage in magnesium hydride. A prototype of the tank was filled with 123 g of previously ball-milled and doped MgH2. About 80 nl of hydrogen can be reversibly stored at a pressure less than 1 MPa. However, owing to the fact that the heat of a reaction limits the absorption and desorption processes, these latter are slowed down. To have a better understanding of the heat and mass transfers in the tank, a numerical model was developed using the Fluent software. The numerical simulations of hydrogen sorption are found to be in good agreement with the experimental results. During desorption, as an example, the reaction occurs locally and progresses from the tank walls towards the core.Low thermal conductivity of MgH2 powder and slow heat evacuation (or supply) are identified to be responsible for the increase in the tank (un)loading duration.A second configuration of the tank was tested with a heat exchanger and a new compacted material, composed of MgH2 and expanded natural graphite (ENG), to increase thermal conductivity. Due to a better controlled heat transfer in the tank, this system can absorb 100 nl H2 in only 25 min.