Modelling the Transient Behavior of Heat Exchangers in Aircraft Engine Preliminary Design

Abstract. Compact heat exchangers must be integrated into advanced aero-engine concepts; therefore, thorough analysis is needed in the preliminary phase. This work advances an early aero-engine heat-exchanger design tool by extending methods beyond stationary analyses to fully transient operation. Flight conditions change within seconds during maneuvers, so pressures, temperatures, and mass flows on both sides of a heat exchanger vary simultaneously. Steady analyses cannot capture response times, while many transient models treat only single-inlet disturbances or simple layouts. High-fidelity simulations are also too slow for broad design sweeps of the preliminary phase. The proposed tool retains the three-dimensional, cell-based framework and solves an unsteady wall energy balance with finite differences to represent thermal inertia. Between cells, fluid enthalpy information is propagated using the concept of residence time, allowing for arbitrary, coupled inlet ramps. Validation against a Modelica benchmark model shows close agreement for fluid temperatures. Runtime remains in minutes on modest hardware, enabling rapid exploration of the parameter space. A multipass counter-crossflow hydrogen conditioner is further evaluated for a Go-Around maneuver, revealing a lag between boundary changes and temperature propagation, as well as a nonlinear dependence of transient duration on ramp time.