利用跨接比容平移SRK方程计算CO2/H2O复合工质pvT(x)性质的研究OA

[Objective]Using a CO2/H2O mixture as the composite working fluid,the supercritical carbon dioxide(S-CO2)semi-closed Brayton cycle can achieve efficient carbon capture and power generation while maintaining operational flexibility.Accurate descriptions of the thermophysical properties of CO2/H2O mixtures are essential for cycle analysis,component design,and system performance optimization.Therefore,it is necessary to develop an equation of state capable of reliably describing the thermophysical properties of CO2/H2O mixtures over the operating range relevant to the S-CO2 semi-closed Brayton cycle.[Methods]In this study,the Kiselev crossover method was adopted to establish crossover volume-translation Soave-Redlich-Kwong(CVTSRK)equations of state,for pure CO2 and pure H2O.The accuracy of the proposed pure-fluid CVTSRK equations was verified through calculations of saturated properties and single-phase pvT properties.On this basis,a CVTSRK equation of state applicable to CO2/H2O mixtures was further established by combining component-based mixing rules with symbolic regression.The proposed equation was applied to single-phase pvTx property calculations for CO2/H2O mixtures,and its correlation accuracy,predictive capability,applicability,and computational performance were evaluated across the temperature-pressure and composition ranges relevant to the S-CO2 semi-closed Brayton cycle.[Results]The results indicate that the proposed CVTSRK equation of state can accurately describe the single-phase pvT(x)properties of pure CO2,pure H2O,and CO2/H2O mixtures from subcritical to supercritical conditions.For the experimental density data of pure CO2 and pure H2O,the average absolute relative deviations between the calculated densities and the experimental data are 0.91%and 1.73%,respectively.For CO2/H2O mixtures,the average absolute relative deviation between the calculated densities and the experimental data is 0.86%.For the data excluded from model fitting,the prediction deviation is only 0.40%,indicating the favorable predictive capability of the proposed equation.Moreover,the equation requires only a few fitting parameters and can be readily integrated into engineering calculation programs.Within the parameter range involved in the S-CO2 semi-closed Brayton cycle,namely temperatures of 298～2 000 K,pressures up to 30 MPa,and CO2 mole fractions of 0.75～1.00,the constructed CVTSRK equation of state exhibits satisfactory applicability and stable computational performance.[Conclusion]The proposed CVTSRK equation of state maintains high accuracy over the range covered by experimental data and provides stable and reliable extrapolative predictions under high-temperature conditions.It also shows reliable performance in data-sparse regions and provides a thermophysical property basis for component design and performance analysis of key processes in S-CO2 semi-closed Brayton cycles,including compression,expansion,and recuperation.Furthermore,the proposed equation can support further studies on cycle mechanisms,system configurations,and performance optimization,and provide a basis for scientific research and engineering applications.