Investigation on the thermodynamic performance and machinery mass in the N2O-based mixtures recompression Brayton cycle for a nuclear-powered spacecraft

Abstract

As a reliable energy system with a long service life, nuclear energy can produce massive power for spacecraft in deep space exploration. Due to the compact layout and excellent performance, the supercritical recompression Brayton cycle has received extensive attention and has become a hot research topic in thermoelectric conversion technology. The critical properties of the working medium are a constraint on the cycle performance. Adding additional gas into a pure S-N2O working medium can effectively change the properties of the critical point and improve the cycle performance. However, there is no standard for selecting appropriate binary mixture components to determine which additive gas can improve cycle efficiency. In this work, several gases are chosen as the potential N2O-based mixtures (N2O-O2, N2O-He, N2O-Kr, N2O-Ar, N2O-H2S, N2O-CO, N2O-SO2, N2O-CH4, N2O-C2H6, N2O-C3H8, N2O-C4H8, N2O-C4H10, N2O-C5H10, N2O-C5H12, N2O-C6H6) as the working medium in the system. The detailed sensitivity analysis reveals the influence of essential parameters (the split ratio, pressure ratio, selection minimum operating temperature, maximum operating temperature, and minimum operating pressure) on the thermodynamic efficiency and Brayton machinery unit mass. According to the analysis results, the thermal efficiency improves with an increase in the split ratio, pressure ratio, and maximum operating temperature and decreases in the selection minimum operating temperature and minimum operating pressure for all mixtures. The exergy efficiency also showed a similar variation trend. However, the influence of the maximum working temperature on it is different from that of the thermal efficiency, which decreases with the increase of the maximum working temperature. The cycles operated close to the critical area can provide better cycle performance, and N2O-He has the best thermal performance among all proposed N2O-based mixtures, which can be used as a potential choice as the working medium for future nuclear-powered spacecraft.