Design and optimal thermal efficiency contrastive analysis on closed Brayton cycle systems with different fluids of fluoride-salt-cooled high-temperature advanced reactor

To match the advantages of Fluoride-Salt-cooled high-Temperature Advanced Reactor, the closed Brayton cycle system was considered as the energy conversion system, and the thermodynamic analysis, conjugate gradient optimization, and exergy analysis were performed. The pinch point constraint method based on simultaneous equations was proposed to improve the calculation efficiency and ensure the unity of comparison standards, and the exergy analysis was used to quantify and optimize the exergy losses for the equipment. The thermodynamic characteristics of the power cycle systems with various fluids were analyzed, including far-critical fluids: air, nitrogen, helium, and argon, and near-critical fluids: carbon dioxide, sulfur hexafluoride, propane, and xenon. The results of the thermodynamic analysis show that for near-critical fluids, the efficiency of the SF6 cycle is the highest reaching 46.6% without considering the chemical reactions, while for far-critical fluids: air and N2, the thermal efficiencies are 45.6% and 45.5% respectively. The thermal efficiency of the far-critical fluid cycle is more sensitive to turbine efficiency, meaning enough thermal efficiency can be achieved without too high adiabatic efficiency of the compressor and isentropic efficiency of the turbine. However, far-critical fluid cycles do not have this characteristic. The results of the exergy analysis show the CO₂ cycle has the highest potential to improve thermal efficiency, which has the highest improvement from 43.48% to 49.31% with the recompression process. The method and conclusion of this paper can provide references for the design and optimization of the Brayton power cycle system.