The supercritical carbon dioxide (S-CO2) Brayton power cycle has been receiving worldwide attention due to the high thermal efficiency and compact system configuration. Because of the incompressible liquid like characteristic (e.g. high density, low compressibility) of the CO2 near the critical point (30.98 °C, 7.38MPa), an S-CO2 Brayton cycle can achieve high efficiency by reducing compression work. In order to utilize the S-CO2 power conversion technology in various applications, such as distributed power generation and marine propulsion, air-cooled waste heat removal system is necessary. However, the critical temperature of CO2 (30.98 °C) is an intrinsic limitation on the system minimum temperature. Because of the small difference with atmospheric temperature, a large amount of cooling air flow or a very large heat exchanger is required to reach the target minimum temperature. In this paper, to improve the system efficiency and ease the problem of air-cooled waste heat removal system, the mixture of supercritical CO2 with other fluids has been studied. Also, the preliminary performance test results of CO2 mixture with pre-existing experimental facility are evaluated.

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