Effect of the thermal insulation layer on non-equilibrium condensation in the nozzle for carbon capture

A non-equilibrium phase transition model, grounded in the classical theory of droplet nucleation and growth, is constructed for the prediction of condensation phenomena in supersonic flows by coupling transport equations with source terms. The study investigates the influence of nozzle insulation on the spontaneous condensation of CO₂. Results show that the maximum supercooling in the non-insulated model is 6.3% higher than in the insulated model, which leads to earlier nucleation of gas in the non-insulated model. To investigate the impact of the condensation model on the gas expansion, a comparison is conducted between a single-phase flow model and a condensation flow model. The results indicate that the single-phase flow model neglects the latent heat released during condensation, leading to an overestimation of the flue gas expansion capacity inside the nozzle. The maximum deviation of the Mach number between the two models reaches 13%. Increasing inlet saturation from 0.172 to 0.222 results in a forward shift of the Wilson point and a decrease in the maximum nucleation rate from 1.3 × 10²² m^-3s^-1 to 5.2 × 10²¹ m^-3s^-1. However, the increase in saturation favors gas liquefaction, leading to a 34% increase in the maximum liquid fraction, from 0.065 to 0.087.