Nonequilibrium condensation of CO₂ in flue gas inside Laval nozzles

A mathematical model for predicting nonequilibrium condensation in high-pressure supersonic flows was established based on phase transition kinetics theory. The nonequilibrium condensation of CO₂ in Laval nozzle was predicted for flue gas (mainly composed of N₂ and CO₂) after desulphurization, denitrification and dehumidification, and the influence of initial saturation on flow behavior and nonequilibrium condensation was elucidated. The results showed that the thermodynamic system entered a nonequilibrium state downstream of Laval nozzle throat, a condensation shock phenomenon occurred at x=0.09 m, and the nucleation rate rapidly increased from 0 to 6.33×10²² m⁻³·s⁻¹. After that, metastable molecules aggregated on the surface of condensation nuclei, leading to droplet growth, and the droplet growth rate increased from 0 to 0.04 m/s in a short time. When the initial saturation increased from 0.11 to 0.19, the drop radius of CO₂ increased from 3.72×10⁻⁸ m to 1.74×10⁻⁷ m, an increase of 2.67 times, and the liquid mass fraction of CO₂ increased from 0.044 to 0.081, an increase of 84.1%. Therefore, the initial saturation should be appropriately increased to obtain a larger liquid mass fraction and droplet radius, thus achieving a better carbon capture effect.