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Fuel as Alternative Heat Sink for Future Aircraft

Bauhaus Luftfahrt investigates fuel as an alternative heat sink to manage future aircraft’s cooling needs. With the introduction of partial electric propulsion systems, cooling requirements are likely to increase by up to an order of magnitude compared to today’s aircraft. For hybrid concepts, fuel poses an excellent alternative as heat sink compared to traditionally used ram air. It has a higher thermal conductivity, heat capacity, and density. It is stored in wing-integrated tanks, which enables the wings to act as heat exchangers with ambient air, without the addition of a drag increment to the aircraft system. Furthermore, the cooling system mass can be reduced due to shorter transmission distances and more compact components.

In a first case study, the Bauhaus Luftfahrt quad fan – a short-range, year-2035+, parallel discrete hybrid-electric aircraft concept with a maximum heat load of 120 kW – was investigated. The first developed model is stationary, but multiple operating points were considered. A fuel flow absorbs all emitted waste heat from the electric propulsion system and circulates underneath the wing skin to enhance heat transfer to ambient. The system is able to remove the entire waste heat during all operating conditions, except for the taxi case. During flight, the conservatively designed system has the capacity to absorb temporary peak loads. The study showed that fuel is a viable alternative heat sink for aircraft with large waste heat loads. The developed model can be refined to further investigate and optimise performance in challenging conditions, such as the taxi case.

  • Thermodynamic model of wing-integrated fuel heat exchanger: Waste heat (Qin) is transferred to cold fuel from the tank. The hot fuel then circulates underneath the wing surface to enhance heat transfer to ambient (Qout).Thermodynamic model of wing-integrated fuel heat exchanger: Waste heat (Qin) is transferred to cold fuel from the tank. The hot fuel then circulates underneath the wing surface to enhance heat transfer to ambient (Qout).
  • Fuel cooling system performance: Actual heat transfer to required heat transfer ratio (Q/Qreq) over fuel flow (wf) for different maximum fuel temperatures at different operation points.Fuel cooling system performance: Actual heat transfer to required heat transfer ratio (Q/Qreq) over fuel flow (wf) for different maximum fuel temperatures at different operation points.