Homogeneous Condensation Mechanism of Water Vapor in Swirling Flow: A Molecular Simulation Perspective

Supersonic separation technology is a natural gas treatment technology with easy processing, low investment, low energy consumption, no need to add chemicals, and environmental protection. However, supersonic separation technology is immature. Furthermore, the accuracy of existing nucleation theories for the droplet nucleation process in the supersonic nozzle remains unclear, because they do not consider the effect of swirling motion. The nucleation and condensation processes of water vapor were investigated via molecular dynamics (MD) simulations in this study, and the effects of cooling temperature, axial velocity, and tangential velocity on swirling flow condensation characteristics were analyzed kinetically and thermodynamically at the microscopic level. It is found that at lower cooling temperatures and higher axial velocities, the induction phase of the water vapor condensation process is shortened, the nucleation rate increases, and nucleation occurs more easily. When the axial velocity increases from 200 to 400 m/s, the nucleation rate increases about twice. When the cooling temperature increased from 313 to 353 K, the nucleation rate decreased by 57.7%. However, changes in tangentials have little effect on water vapor swirling flow condensation characteristics.