Integrated optimization of refrigerant distribution control and air-side geometry for compact two-row multi-pass microchannel evaporators in electric vehicles

With the transition toward electric vehicles, the demand for efficient thermal management has increased. Microchannel evaporators for vehicle air conditioning must deliver high cooling capacity within a limited packaging space, but refrigerant maldistribution in two-row, multi-pass configurations reduces the effective utilization of the heat-transfer area. Previous studies have examined refrigerant-distribution measures and air-side geometries separately, whereas refrigerant-distribution control has rarely been treated as an optimization variable or designed together with the air-side geometry. This study therefore addresses how refrigerant-distribution control and air-side geometry can be optimized jointly to improve the heat transfer rate per frontal area while balancing pressure-drop penalties. A segment-wise ε-NTU model coupled with a pressure-balance refrigerant-distribution model was developed and validated against ten prototype evaporators. The pass arrangement and the baffle-bypass position and area ratios were formulated as design variables together with the fin and louver geometry, and XGBoost surrogate models trained on a two-stage design of experiments were coupled with NSGA-III and TOPSIS to derive an optimal design. Compared with the baseline, the optimized design increased the heat transfer rate per frontal area by 21.4% while reducing the frontal area by 20.5%; the refrigerant maldistribution index and the air-side pressure drop decreased by 56.9% and 7.4%, respectively, while the refrigerant pressure drop increased by 6.5% but remained within the constraint. The optimized design maintained lower refrigerant maldistribution over air flow rates of 300–500 m 3 ·h −1 . These results show that jointly optimizing refrigerant-distribution control and air-side geometry enables compact, high-performance evaporators for packaging-constrained electric vehicles.