Optimization of a recompression supercritical nitrous oxide and helium Brayton cycle for space nuclear system

Long life, high energy density, high efficiency, and compact power system is necessary for space exploration to achieve a future goal. Recompression supercritical Brayton cycle has excellent potential for application of space nuclear power generation systems. However, it faces the choice of cycle working fluid which limits the cycle thermal efficiency and quality. In order to improve the thermal efficiency of the nuclear power system, a new composition of the working fluid, nitrous oxide and helium (N₂O–He) mixture is used in the system. Comprehensive studies and optimization are performed for the significant parameters, including the split ratio, pressure ratio, minimum operating temperature, maximum operating temperature, and minimum operating pressure. Optimum values have been obtained at which the maximum thermal efficiency and minimum Brayton rotating unit (BRU) mass of the cycle occur. Results show that the thermal efficiency improves with an increase in the split ratio, main compressor pressure ratio, and maximum operating temperature, and decreasing minimum operating temperature and minimum operating pressure. The proposed novel working fluid cycle has superior performance compared with N₂O (deviation of 5.1%) and CO₂ (deviation of 6.5%). The optimized thermal efficiency and BRU mass are calculated as 42.67% and 3584.80 kg at optimum conditions.