An innovative model of supercritical nitrous oxide thermophysical properties for the recompression Brayton cycle

Supercritical nitrous oxide (S-N₂O) is an environmentally friendly gaseous medium with advantages including good stability, favorable nuclear properties, appropriate safety performance, and reasonable operational costs, making it suitable as a working fluid in thermal cycles. The significant impact of pressure and temperature on the physical properties of supercritical N₂O in a recompression Brayton cycle poses constraint on the cycle conditions, particularly in the vicinity of the critical point. To conduct more accurate research on the physical property characteristics of N₂O, an N₂O gas property calculation model (S-W-H) was developed by integrating the REFPROP software, the Span-Wanger (S-W) equation, and the Helmholtz free energy. Furthermore, calculations of N₂O physical property parameters were performed, resulting in precise N₂O physical property parameters. The thermal efficiency and exergy efficiency S-N₂O recompression Brayton cycle under basic operating conditions are 43.00% and 56.80%, respectively. Compared with the experimental values reported in existing literature, the error range for thermophysical properties is within 2%, whereas that for the Brayton cycle thermal efficiency is 2.02%.