Water-Evaporation Supported Fuel-Cell Cooling Architectures for Aircraft

Kurzfassung

The thermal management-induced drag of conventional ram-air cooling systems for low-temperature fuel-cell propulsion can account for roughly 20\% to 25\% of total drag in fuel-cell aircraft concepts, while its mass and power impact at the overall aircraft level are far less significant. This drag penalty can severely reduce efficiency, especially when additional parallel power sources for takeoff such as gas turbine engines are undesirable. To address this, we propose augmenting low- and medium-temperature fuel-cell cooling with an auxiliary water-evaporation system. This mechanism is used only when needed, primarily during takeoff in hot ambient conditions, while the ram-air system can be downsized to meet cruise requirements. Water evaporation can achieve coefficients of performance of 50 to 100, while reducing the required mass flow by two orders of magnitude. It provides a heat-rejection energy density of approximately 670 Wh/kg, far exceeding that of state-of-the-art high-power-density batteries. Furthermore, the resulting vapor can be vented overboard, and the system is expected to outperform batteries in reliability, durability, and environmental impact. The paper introduces several architectures for integrating water-evaporation cooling into aircraft systems and discusses their respective advantages, limitations, and implications for overall aircraft performance. Initial results indicate that enabling evaporative cooling can significantly reduce the required ram-air channel size and drag, offering a promising pathway to more efficient fuel-cell-powered aircraft. In the EU project TheMa4HERA, aircraft-level design trades and scaled experimental validation for aviation applications of water evaporation are planned in 2026.