Assessment of Metal Hydride Reactors as Thermal Management Enhancement of Hydrogen Fuel Cells in Electric Aircraft

Abstract

Electrified propulsion systems have the potential to reduce the environmental impact of aviation. Hydrogen fuel cells as primary energy supplier are a promising technology to power the electrically-driven propulsors. However, the thermal management of fuel cells is challenging due to their high amount of excess heat energy at a typically low temperature level. This work investigates the cooling potential of metal hydride (MH) reactors to enhance the thermal management system (TMS) of low temperature fuel cells. As a secondary function, the MH reactor can serve as an emergency hydrogen supply. There are two operation concepts of MH reactors considered in this study. In the first operation concept, the MH acts as a heat sink by absorbing some share of the heat of the fuel cell. This decreases the amount of heat to be removed by the TMS. In the second operation concept, the MH reactor operates as a heat pump to enlarge the temperature difference in the heat transfer fluid cycle. This improves the performance of the heat exchanger of the TMS to reject heat to the ambient air. For both operation modes, a sizing of an MH reactor and a heat exchanger is performed to estimate the impact on the TMS. While an exemplary general aviation aircraft serves as calculation example, the results are also applicable to commuter and regional aviation aircrafts. The study shows, that MH reactors have the potential to reduce the size of the heat exchanger significantly. In quasi-continuous heat pump operation, an MH reactor allows a reduction of the heat exchanger dimensions of up to 8 %. If the maximum heat rejection during take-off determines the heat exchanger size, a reduction of even 39% is reasonable when the MH reactor operates as a heat sink.