System-component combined design and comprehensive evaluation of closed-air Brayton cycle

A microreactor power system possesses characteristics such as efficiency, compactness, and high adaptability to the environment. This paper proposes a microreactor thermoelectric conversion system based on a closed-air Brayton cycle, where the basic parameters of the cycle parameters and components are designed. Herein, the system-component combined design method is applied, which combines the cycle thermodynamic model with the component design method to iteratively correct the cycle thermodynamic calculations and component design results. A system power density index, i.e., the net output power per unit system volume, is proposed to comprehensively evaluate the efficiency and compactness of the system. This study investigates the impact of cycle pressure ratio, compressor inlet temperature, cooler exhaust temperature, and recuperator effectiveness on the thermodynamic performance index (cycle efficiency, system power density, and components exergy destruction rate). It is observed that the system power density increases initially and decreases subsequently within a certain range of the design parameters. Finally, a genetic algorithm tool is employed to optimize the cycle parameters using system power density and cycle efficiency as optimization objectives. The optimization results demonstrate that the maximum system power density is 402.34 kW/m³ and the corresponding cycle efficiency and system volume are 24.86% and 3.09 m³, respectively. When the system total volume is limited under 5 m³, the maximum cycle efficiency is 31.09% and the corresponding power density is 310.9 kW/m³.