Radiators in fuel cell powered aircraft: the effect of heat rejection on drag

• A thermodynamic approach and analysis to size a ducted fan and radiator. • Analysis of a ducted radiator at cruise for a hydrogen fuel cell powered aircraft. • Reductions in power consumption, mass, and drag with stack temperature. Proton Exchange Membrane Fuel Cell (PEMFC) powered propulsion is anticipated to play a leading role in decarbonising aviation. Megawatts of heat generated by PEMFCs must be transferred to atmosphere via cooling systems, and the drag incurred by these systems can be offset by heat dissipation to the airstream via ducted radiators, a phenomenon termed the ‘Meredith effect’. This phenomenon is relatively unexplored for ducted radiators on aircraft. This paper therefore presents thermodynamic analysis that provides unprecedented insight into the fundamental physics of the problem and demonstrates that it is feasible to develop fan-fed ducted radiators with low drag for 1 MW PEMFC propulsion systems at stack temperatures of 80 to 200 °C. Parameters relevant to ducted radiators were analysed for several flight-representative cases to investigate their effect on specific thrust, and radiator exit temperature and frontal area. This detailed study enabled the duct and inlet fan assembly to be sized for zero internal drag. A multi-objective Genetic Algorithm was subsequently used to develop optimised radiators for this duct for 80 °C, 120 °C and 200 °C stack temperatures. The results demonstrated that increasing stack temperature from 80 to 200 °C had several favourable effects: the radiator frontal area reduced by ∼55 %, the radiator core mass decreased from ∼8 kg to ∼3.6 kg, the fan assembly efficiency improved by ∼7 %, and the predicted external drag reduced by ∼36 %. The approach and findings from this study provide important information for the design and realisation of PEMFC powered aircraft propulsion systems.