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Investigation on the temperature sensitivity of the S-CO2 Brayton cycle efficiency

Wang, Lin, Pan, Liang-ming, Wang, Junfeng, Chen, Deqi, Huang, Yanping, Hu, Lian
Energy 2019 v.178 pp. 739-750
heat exchangers, temperature, thermodynamics
With the development of compact heat exchangers in the past few decades, S-CO2 recompression Brayton cycle has attracted much attention. However, the cycle efficiency of the traditional S-CO2 recompression Brayton cycle is sensitive to the compressor inlet temperature, which limits the application of the cycle. According to the property of S-CO2, rapid property change appears in different temperature region under different pressure conditions in pseudocritical area. This feature can be used to reduce recompressing compressor work. To take the advantage of this feature, a modified recompression Brayton cycle based on S-CO2 recompression Brayton cycle is proposed to decrease the temperature sensitivity of recompression Brayton cycle efficiency. Different minimum pressure and different flow split ratio conditions are investigated under various minimum temperature ranges. In this paper, the temperature sensitivity of the cycle efficiency is investigated by an in-house cycle analysis code in the minimum temperature range of 32–50 °C and the minimum pressure range of 7.6–9.0 MPa. First and second law of thermodynamics are used to analyze the performance of the two kinds of Brayton cycle. Results show that the modified recompression Brayton cycle has better temperature sensitivity while having comparable cycle efficiency as the recompression Brayton cycle. Moreover, high compressor inlet pressure and small flow split ratio can decrease the temperature sensitivity of cycle efficiency.