High performance reactor of a metal hydride based cooling system for air-conditioning of fuel cell electric vehicles

Abstract

Refueling fuel cell electric vehicles (FCEVs) needs energy for the compressor at the refueling station that is afterwards stored inside the high-pressure tank on board of the vehicle. On the one side, the State of the Art does not allow to recover this energy which results in a negative impact on the efficiency chain of a FECV. On the other side, air-conditioning systems in vehicles consume significant amounts of energy, further reducing the limited driving range and increasing the operation costs. This problem can be addressed by the open metal hydride cooling system (MHCS) arranged between the pressure tank and fuel cell, that converts the available potential energy into a heat pump effect. The challenges of the MHCS is its thermal performance referred to the amount of metal hydride (MH) that is required. This study presents a reactor design that significantly increases the specific cooling power of previous MHCS. The new reactor features MH-graphite composites and micro fluid channels for heat transport enhancement as well as an additive-manufactured lightweight structure of aluminum to reduce sensible losses. Experimental characterization at a pressure ratio of 7, a cold side temperature of 20 °C and hot side temperature of 30 °C show a specific cooling power of 522 W kg_MH⁻¹, that is nearly twice as high as the best value reported in the literature. Furthermore, not only cooling efficiencies above 60 % could be maintained on higher specific power, but also the performance at an elevated temperature lift of 20 K is improved in comparison to previous systems. The experimentally proven high performance verifies the good heat and mass transport properties with a low structural heat capacity at the same time. This significantly improved reactor allows to meet the demanding requirements in terms of weight, space and cost for the applications in the mobile application such as a FCEV.