Scenario-adapted design of hybrid working fluids: A thermo-hydraulic study in airfoil-fin PCHEs for terrestrial power generation and space exploration

In nuclear energy systems, the closed Brayton cycle serves as a key solution for efficient thermal-to-power conversion, with applications spanning terrestrial power generation and space exploration. Critical to these systems are printed circuit heat exchangers (PCHEs), valued for their high compactness, excellent heat transfer, and resistance to extreme conditions. However, comparative studies on CO2-based and helium-based mixtures in airfoil-fin PCHEs remain limited, particularly regarding their performance under different critical temperatures for terrestrial use and various He-Xe molecular weights and other candidate mixtures in space. To fill this gap, numerical simulations are conducted to examine selected mixtures in airfoil-fin PCHEs. For space exploration, the thermal-hydraulic performance of He-Xe blends (15 and 40 g/mol) and a He-CO2 mixture (20 g/mol) is investigated; for terrestrial power generation, CO2-Xe and CO2-H2S mixtures (critical temperatures 30 °C and 35 °C) are evaluated against supercritical carbon dioxide (sCO2). Results indicate that in space exploration, He-CO2 offers the best overall performance, with a performance evaluation criterion (PEC) 29–44% higher than that of He-Xe (40 g/mol) and 9–15% higher than that of He-Xe (15 g/mol). For terrestrial power generation, CO2-H2S improves PEC by 1–1.2% through enhanced heat transfer, while CO2-Xe achieves a 0.74% increase via reduced flow resistance. This work provides guidance for selecting suitable mixtures in airfoil-fin PCHEs for closed Brayton cycles across both domains.