Thermodynamic optimization of closed air Brayton cycle and air-ORC combined cycle

In order to improve the flexibility and adaptability of small mobile nuclear power systems, air is considered as an optional working fluid of nuclear Brayton cycle system. It can avoid the shortage of working fluid under extreme conditions, and ensure the system operation with tight working fluid supply. In this study, simple regenerative cycle (SRC), intercooling regenerative cycle (IRC) and corresponding air-ORC combined cycle (SRCC and IRCC) are proposed and modeled. Thermodynamic analysis of key parameters is conducted. Genetic algorithm (GA) is applied for multi-parameter optimization to achieve the maximum cycle efficiency. With the increase of pressure ratio (PR), the efficiency of SRC increases firstly and then decreases. Pressure ratio corresponding to the maximum cycle efficiency increases gradually with turbine inlet temperature. The efficiency of IRC is slightly lower than that of SRC in low pressure ratio region, but IRC maintains a higher efficiency in high pressure ratio region. For SRCC, isobutane has the best performance among three selected organic working fluids. The multi-parameter optimization result indicates that the IRCC has lower cycle efficiency comparing with SRCC, and SRCC shows the optimal performance among the four configurations.