Properties of Nitrous Oxide and Helium mixtures for space nuclear recompression Brayton cycle

Space nuclear reactors are the research foundation of space nuclear power and nuclear propulsion. Thermoelectric conversion efficiency and mass of high-power nuclear reactors have always been essential factors that restrict aerospace design. Supercritical nitrous oxide (S-N₂O) Brayton cycle is becoming hot research due to its high-power conversion efficiency, low energy loss, compact and simple system structure, making it widely used in space nuclear reactor application. The recompression cycle is proposed to improve the thermal efficiency of the S-N₂O cycle and effectively weaken the “pinch point” phenomenon that may occur in the regenerators. The thermodynamic of the S-N₂O Brayton cycle has been studied but has little research on the nitrous oxide (N₂O) and helium (He) mixtures as the working medium for the Brayton cycle. In this paper, physical properties were studied on the mixture of supercritical nitrous oxide and helium (S-N₂O+He) as the working medium of the space power system based on a recompression Brayton cycle. Consider the thermodynamic properties of the mixture at seven different temperature nodes, analyze the variation trend of compressibility factor, specific heat, specific heat ratio, thermal conductivity, and dynamic viscosity with temperature, respectively. Finally, determined the mixing ratio of the working medium at the maximum thermoelectric conversion efficiency of the cycle and estimated the mass and specific mass of the Brayton rotating unit.