Thermal-hydraulic performance of pin-fin channels with tapering profile in high-effectiveness PCHE recuperators for space Brayton cryocoolers

The increasing demand for high-capacity reverse Brayton cryocoolers in space applications has highlighted micro pin-fin printed circuit heat exchangers (PCHEs) as promising recuperators. However, the photochemical etching process used in PCHE fabrication creates tapered pin-fin profiles that differ from idealized geometries. The effects of these profiles on heat transfer and flow performance remain poorly understood, creating challenges for recuperator design and optimization. Therefore, this study systematically investigates the thermal-hydraulic performance in etched pin-fin channels with cryogenic working fluids. The results demonstrate that the tapered etched profile significantly enhances heat transfer performance and deteriorates flow performance, with lifting the Nusselt number ( Nu ) and friction factor ( f ), up to 29.0 % and 48.4 % compared to idealized pin-fin geometries. The influence of geometric parameters on flow and heat transfer performance in etched pin-fin channels (pin-fin diameter of 0.3 mm) is also examined, including transverse pitch ( T = 1.1–2.0 mm), streamwise pitch ( S = 1.1–2.0 mm), and pin-fin height ( H = 0.1–0.4 mm). Both radial and streamwise local Nu distributions are analyzed across these configurations to elucidate the underlying impacts of these geometry parameters. Based on simulations with representative cryogenic fluids (nitrogen, neon, and helium), the Nu and f correlations for the etched pin-fin channel are proposed, covering common cryocooler usage with Prandtl numbers ranging from 0.67–0.92. These correlations improve the prediction deviations for pin-fin channels with etched profiles, achieving mean prediction deviations of 8.9 % and 13.0 % for Nu and f , respectively. The findings provide guidance for high-effectiveness PCHE design and optimization in space cryocoolers.