Numerical study on CO₂ non-equilibrium condensation considering shock waves for the potential of flue gas decarbonization

This work proposes a CFD model based on spontaneous condensation theory and evaluates the potential of non-equilibrium phase transition principle for flue gas decarbonization in supersonic separators. The effects of inlet supercooling degree and convergent curve on non-equilibrium condensation behavior of CO₂ and shock wave are discussed in detail. Based on the gas equation of state, the influence of thermodynamic model on flow behavior and non-equilibrium condensation process is quantified. The results show that increased inlet supercooling prolongs droplet growth process and increases liquid fraction in the separator. When the inlet supercooling increases by 10 K, the liquid fraction increases by 38.5%. Using Translation of Witoszynski curve and Witoszynski curve to design the converging part of the separator can simultaneously obtain larger droplet size and higher liquid fraction, which is conducive to the liquefaction and separation of CO₂. The ideal gas model overestimates the expansion level of flue gas and underestimates the liquid produced by spontaneous condensation, with errors of 4.03% and 28.5%, respectively.