Surface Tension Effects on Post-Nucleation Growth of Water Microdroplets in Supersaturated Gas Mixtures

Immediately after nucleation in a superheated gas mixture, the very small size of liquid droplets affects the condensation growth of the droplets in two ways: (1) The droplet size may be comparable to the mean free path of the gas molecules, resulting in noncontinuum transport effects, and (2) surface tension effects may strongly alter the conditions at the interface of the droplet. In the study reported here, a direct simulation Monte Carlo scheme was used to model the molecular transport during quasi-equilibrium condensation growth of water microdroplets in a supersaturated mixture of water vapor and a noncondensable gas. In the simulation, the boundary condition at the droplet surface is treated in a manner that allows us to model surface tension effects on transport. Results of calculations are presented for water vapor and argon mixtures for which some experimental data on droplet growth rates exists. The simulation results indicate that surface tension effects play a significant role in the determination of droplet growth rates during early stages of droplet growth. In particular, the results indicate that the droplet growth rate, droplet temperature, and the temperature slip at the interface pass through maxima as the droplet grows. These trends are a consequence of the shift in equilibrium vapor pressure due to surface tension effects at small droplet radii. [S0022-1481(00)02702-X]