A Multiscale Approach for the Thermo-Hydraulic and Structural Performance Prediction of Compact Cross Flow Heat Exchangers

The design of compact heat exchangers (HXs) for hydrogen fuel cell and battery-electric aircraft presents unprecedented challenges in terms of thermal management and structural integration. This study introduces an open-source multiscale–multiphysics framework for predicting the thermo-hydraulic and structural performance of cross-flow HXs based on repeated unit cells. The framework combines detailed microscale conjugate heat transfer simulations with macroscale modelling through two complementary reduced-order strategies: upscaling and homogenisation. The reduced-order models are benchmarked against fullscale, high fidelity simulations. Results demonstrate good agreement of both the upscaled and homogenised models with full-scale CFD simulations, particularly deviations below 4 % for fluid temperatures, with the upscaled model performing consistently better.