Experimental and numerical investigation of a high-effectiveness cryogenic PCHE for space 80 K Brayton cryocooler

Growing space cooling demand has made reverse Brayton cryocooler a promising technology, requiring higher effectiveness and lighter weight recuperative heat exchangers. This study proposes a novel cryogenic printed circuit heat exchanger (PCHE) design for an 80 K space Brayton cryocooler, with both high thermal performance and compactness. Unlike conventional PCHEs, the proposed cryogenic PCHE features high-density micro-fins (114 cm^-2) and a thin wall (wall thickness of 0.1 mm), achieving a compactness of 4548 m²·m^-3, 82 % higher than conventional designs. A counter-flow heat transfer model is developed, incorporating axial heat conduction effects typically overlooked in PCHE design models. Through systematic optimization, the cryogenic PCHE achieves a heat duty of 2.2 kW for gas neon between 80 K and 313 K, with compact core dimensions of 460 mm × 86 mm × 82 mm. Experimental testing demonstrated the exceptional performance of the cryogenic PCHE, achieving a heat transfer effectiveness of 97.3 %, surpassing conventional PCHEs, with only a 7.6 kPa total pressure drop. Compared to conventional plate-fin heat exchangers (PFHE) used in ground Brayton cryocoolers, the cryogenic PCHE shows superior performance. This design achieves a performance evaluation criterion of 1.8, while reducing 80 % volume requirements at equivalent thermal effectiveness. Additionally, the analysis reveals a 1.2 % effectiveness deterioration due to axial conduction, which leads to an 87.4 % overestimation of the cryocooler's cooling capacity, highlighting its significance in high-effectiveness cryogenic heat exchanger design.