Thermal–Hydraulic Performance Comparison of Printed Circuit Heat Exchangers with Identical-Size and Hybrid-Size Unit Channels

The supercritical carbon dioxide Brayton cycle has been identified as being applicable in a wide variety of applications, and printed circuit heat exchangers (PCHEs) are widely used in these applications due to their good compactness and high thermal efficiency. A PCHE with hybrid-size unit channels has been proposed and found capable of improving the heat transfer performance, but most results were obtained at non-consistent total volume and mass flow rate. Therefore, given the space constraints of heat exchangers in supercritical CO 2 Brayton cycles, this study investigates the application of standard-size and hybrid-size unit channel configurations under different hot-to-cold fluid thermal resistance ratios while maintaining a fixed total volume and consistent total mass flow rate. The results demonstrate that the hybrid-size unit channel configuration fails to enhance heat transfer. The heat transfer rate per volume exhibits a marginal 5.2% reduction at smaller thermal resistance ratios and a drastic 28.9% degradation at larger thermal resistance ratios. The hybrid-size channel configuration significantly improves the pressure drop per unit length on the hot side, achieving maximum reductions of 80.3% and 79.7% under the two thermal resistance ratios, respectively. The enhancement magnitude on the hot side outweighs the increased pressure drop on the cold side. Simultaneously, the ratio of average heat transfer rate to total pumping power exhibits significant differences between the two channel configurations under varying thermal resistance ratios. Under scenarios with substantial thermal resistance disparities, the hybrid-size unit channel configuration achieves a maximum 356.2% improvement in the ratio compared to the identical-size unit channel configuration, whereas balanced thermal resistance ratios lead to a degradation in overall performance.