Supercritical Carbon Dioxide Shock Behaviour Near the Critical Point
Published in In the proceedings of Volume 12: Supercritical CO2, 2023
Abstract:
This paper aims to provide an understanding of sCO2 inviscid adiabatic normal shock behaviour near the critical point and to develop an explicit tool for faster prediction of the shock relations that can aid the supercritical turbomachinery design process. An iterative algorithm was developed to compute shockwave behaviours for non-ideal fluids. Three important shock behaviour parameters were investigated: post-shock Mach number, shock strength, and polytropic efficiency. A comparative study was carried out between air (ideal gas assumption), ideal gas CO2 (ideal gas assumption), and non-ideal fluid CO2 (Span-Wagner equation of state). The distinct differences show the inadequacy of the perfect gas shock relations when predicting sCO2 shock behaviour near the critical point. The results of non-ideal fluid calculations show a general trend of stronger shock strengths and higher polytropic efficiencies towards lower pre-shock entropy conditions. This is also distinctive near the critical point due to the reduced speed of sound. Finally, explicit expressions for these parameters were retrieved using symbolic regression. The fitted models have significant improvements compared to the prediction from perfect gas shock relations with a 5-20% point reduction in relative errors. This study also shows the potential for machine learning to be applied in non-ideal fluids effects modelling and the methodology developed in this paper can be easily introduced to other working fluids in their ranges of interest.
Recommended citation:
Jinhong Wang, Teng Cao, Ricardo Martinez-Botas, "Supercritical Carbon Dioxide Shock Behaviour Near the Critical Point." In the proceedings of Volume 12: Supercritical CO2, 2023.