Study of heat transfer and kinetics parameters influencing the design of heat exchangers for hydrogen storage in high-pressure metal hydrides

This paper discusses the challenges of using hydrogen fuel cells to power light-duty vehicles. Storing sufficient amounts of hydrogen to cover adequate travel distances before refueling is one of the more pressing challenges, and different materials have been recommended to enhance storage capacity. This study concerns one class of storage materials called high-pressure metal hydrides (HPMHs). The most important component of a hydrogen storage system utilizing HPMHs is the heat exchanger, which, aside from storing the HPMH, must providing sufficient cooling during the hydrogen refueling to achieve the required short fill time of less than 5 min. Discussed in this paper are practical heat exchanger design guidelines for storage systems employing materials with high rates of heat generation during refueling. Most important among those is the maximum distance between the HPMH powder and the cooling surface, which, for Ti1.1CrMn, must be kept below 10 mm to achieve a fill time of 5 min. A new parameter called non-dimensional conductance (NDC) is developed, which serves as a characteristic parameter to estimate the effects of various parameters on the reaction rate. Overall, it is shown that the hydrogen fill time is sensitive mostly to the effective thermal conductivity of the HPMH and the coolant’s temperature, followed by the contact resistance between the powder and cooling surface.