Effect of shock wave on nucleation and droplet growth of CO₂ in flue gas in supersonic separators

To reduce carbon emissions caused by fossil fuel combustion, this work evaluates a potential carbon capture method. Based on heat transfer theory, aerodynamics and condensation dynamics, a mathematical model is proposed to depict the nonequilibrium condensation of CO₂ in flue gas (N₂–CO₂). The interaction between shock wave and non-equilibrium condensation is clarified. The results show that when the shock wave enters nucleation area, the nucleation process is rapidly terminated and droplet growth process disappears. After the shock wave, the supersaturation decreases rapidly from 2.26 to 0.19, the gas changes from supersaturated state to unsaturated state, and the system returns to the thermodynamic equilibrium state. When the shock wave appears in the droplet growth area, there is a complete nucleation process. The gas molecules in front of the shock wave form stable droplets and release latent heat, leading to the fluctuation of temperature and pressure. After the shock wave, the droplet growth environment is destroyed, resulting in droplet radius and liquid content drop to 0. Increasing CO₂ content can not only reduce the impact of shock wave on flows, but also strengthen the heat and mass transfer, and obtain larger droplet radius and higher liquid content.