Abstract
The article deals with the energy and exergy performance analyses of supercritical carbon dioxide recompression Brayton cycle (S-CO2 RBC). This cycle is known to offer maximum efficiency when operating near the critical point of CO2, which is possible in low ambient temperature environment but not in warm or hot ambient conditions. CO2-C7H8 binary mixture is used to improve the thermodynamic performance of the cycle for warmer ambient conditions. The percentage of C7H8 in the mixture is selected according to cycle’s minimum temperature, which is assumed 50oC. When using CO2-C7H8 binary mixture, the analysis shows that the thermal efficiency of the cycle is improved by nearly14.5% and 8% for turbine inlet temperatures of 350oC and 400oC, respectively. Moreover, exergetic performance analysis reveals better performance of RBC with CO2-C7H8 binary mixture.
Highlights
Increasing demand of electrical power raises a global concern due to rapid depletion of fossil fuel
Energetic and exergetic analysis of recompression Brayton cycle operating with pure CO2 and CO2-C7H8 binary mixture are presented to compare the efficacy of the two working fluids for the regions with warm ambient temperatures
Thermal efficiencies and related parameters of the cycles were computed and shown in table 1. It is evident from the data, that the recompression Brayton cycle (RBC) with CO2-C7H8 binary mixture perform much better than RBC with CO2 with nearly 11% improvement in thermal efficiency
Summary
Increasing demand of electrical power raises a global concern due to rapid depletion of fossil fuel. Operating SCO2 BC in high ambient temperature regions poses a problem of cooling CO2 to it critical temperature, adversely affecting the thermal efficiency of the cycle This issue can be managed by raising the critical temperature using CO2 based binary mixture [7, 8]. Seungjoon et al performed preliminary study on the selection of additives for s-CO2 power cycles with R-123, R-134a, R-22, R-32, C7H8, and SF6 They concluded that the BC perform better thermodynamically when using CO2-R32 and CO2-C7H8 binary mixtures as working fluids instead of pure CO2 [11]. Energetic and exergetic analysis of recompression Brayton cycle operating with pure CO2 and CO2-C7H8 binary mixture are presented to compare the efficacy of the two working fluids for the regions with warm ambient temperatures. The deviation from the experimental data is apparent at higher concentration levels of C7H8 that are not considered in this study
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