Thermal-hydraulic performance of a composite-channel printed circuit heat exchanger precooler for supercritical CO2-based mixtures

Printed circuit heat exchanger (PCHE) precoolers operating with CO 2 -based mixtures and water exhibit asymmetric thermal-hydraulic requirements on the hot and cold sides. However, conventional PCHE precoolers often employ identical channel geometries on both sides, and the side-specific allocation of flow-enhancement structures remains insufficiently clarified. This study investigates the side-specific allocation of airfoil-fin enhancement between the hot and cold sides through a two-stage three-dimensional numerical analysis of a composite-channel PCHE precooler. In the first stage, straight and airfoil-fin channels were combined into four hot-side/cold-side configurations. Pure CO 2 , CO 2 /propane, and CO 2 /R32 mixtures with a 20 wt% additive fraction were considered under different water-side mass flow rates. The results showed that the A-S configuration maintained a relatively low hydraulic penalty while providing additional heat-transfer enhancement across all investigated working fluids and flow conditions, and was therefore identified as a robust compromise. Among the two additives, R32 exhibited a more favorable thermal-hydraulic performance than propane and was selected for the subsequent composition-dependent analysis. In the second stage, the effects of R32 mass fraction were investigated in the selected A-S configuration. Increasing the R32 mass fraction caused a more pronounced downstream decline in the local hot-side Nusselt number at higher water-side mass flow rates, while progressively reducing the hot-side pressure drop. These results provide guidance for side-specific channel allocation and working-fluid selection in compact PCHE precoolers for supercritical CO 2 -based mixture power cycles.