It is generally acknowledged that using CO2-based binary mixtures as working fluids in supercritical recompression Brayton cycle for waste heat recovery is a promising technique. This study examines the performance of CO2-Kr (0.76/0.24) and CO2-Xe (0.56/0.44) mixtures, comparing them with pure CO2. Both thermodynamic and thermo-economic considerations are taken into account to establish optimal parameter settings. The findings suggest that the minimum system temperature should be around but not below the critical temperature of the working fluid. The system performs badly at lower pressures and shows nearly the same at higher pressures, with 25 MPa being the recommended value for the main compressor. When the system split ratio and the low temperature recuperator temperature difference are well matched, the heat exchangers exhibit an optimal temperature distribution. The exergy loss distributions of the exchangers in the CO2-Kr and CO2-Xe systems are likewise rather uniform when the input pressure of the main compressor is above the critical pressure of the fluid, typically between 0.2 MPa and 0.4 MPa, enhancing system efficiency. The corresponding temperature difference of the LTR should be within 5 °C above or below the critical temperature of the fluid. This advantageous feature is not immediately apparent in the pure SCO2 cycle.

中文翻译：

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三种二氧化碳基二元混合物在熔盐储能超临界布雷顿循环中的比较分析


人们普遍认为，在超临界再压缩布雷顿循环中使用基于二氧化碳的二元混合物作为工作流体进行废热回收是一种很有前途的技术。本研究检验了 CO2-Kr (0.76/0.24) 和 CO2-Xe (0.56/0.44) 混合物的性能，并将其与纯 CO2 进行比较。建立最佳参数设置时要考虑热力学和热经济因素。研究结果表明，最低系统温度应约为但不低于工作流体的临界温度。该系统在较低压力下表现不佳，而在较高压力下表现几乎相同，主压缩机的推荐值是 25 MPa。当系统分流比和低温换热器温差良好匹配时，换热器表现出最佳的温度分布。当主压缩机的输入压力高于流体的临界压力（通常在 0.2 MPa 至 0.4 MPa 之间）时，CO2-Kr 和 CO2-Xe 系统中交换器的火用损失分布同样相当均匀，从而提高了系统效率。 LTR相应的温差应在流体临界温度上下5°C以内。这一有利特征在纯 SCO2 循环中并不会立即显现出来。