| Summary: | As one of the promising technologies to meet the increasing demand for electricity, supercritical CO<sub>2</sub> (S-CO<sub>2</sub>) Brayton cycle has the characteristics of high efficiency, economic structure, and compact turbomachinery. These characteristics are closely related to the thermodynamic properties of working fluid. When CO<sub>2</sub> is mixed with other gas, cycle parameters are determined by the constituent and the mass fraction of CO<sub>2</sub>. Therefore, in this contribution, a thermodynamic model is developed and validated for the recompression cycle. Seven types of CO<sub>2</sub>-based mixtures, namely CO<sub>2</sub>-Xe, CO<sub>2</sub>-Kr, CO<sub>2</sub>-O<sub>2</sub>, CO<sub>2</sub>-Ar, CO<sub>2</sub>-N<sub>2</sub>, CO<sub>2</sub>-Ne, and CO<sub>2</sub>-He, are employed. At different CO<sub>2</sub> mass fractions, cycle parameters are determined under a fixed compressor inlet temperature, based on the maximization of cycle efficiency. Cycle performance and recuperators’ parameters are comprehensively compared for different CO<sub>2</sub>-based mixtures. Furthermore, in order to investigate the effect of compressor inlet temperature, cycle parameters of CO<sub>2</sub>-N<sub>2</sub> are obtained under four different temperatures. From the obtained results, it can be concluded that, as the mass fraction of CO<sub>2</sub> increases, different mixtures show different variations of cycle performance and recuperators’ parameters. In generally, the performance order of mixtures coincides with the descending or ascending order of corresponding critical temperatures. Performance curves of these considered mixtures locate between the curves of CO<sub>2</sub>-Xe and CO<sub>2</sub>-He. Meanwhile, the curves of CO<sub>2</sub>-O<sub>2</sub> and CO<sub>2</sub>-N<sub>2</sub> are always closed to each other at high CO<sub>2</sub> mass fractions. In addition, with the increase of compressor inlet temperature, cycle performance decreases, and more heat transfer occurs in the recuperators.
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