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 s ize of liquid droplets affects the condensation growth of the droplets in t wo ways: (1) The droplet size may be comparable to the mean free path of th e gas molecules, resulting in noncontinuum transport effects, and (2) surfa ce tension effects may strongly alter the conditions at the interface of th e droplet. In the study reported here, a direct simulation Monte Carlo sche me was used to model the molecular transport during quasi-equilibrium conde nsation growth of water microdroplets in a supersaturated mixture of water vapor and a noncondensable gas. In the simulation, the boundary condition a t the droplet surface is treated in a manner that allows us to model surfac e tension effects on transport. Results of calculations are presented for w ater vapor and argon mixtures for which some experimental data on droplet g rowth rates exists. The simulation results indicate that surface tension ef fects 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 ar e a consequence of the shift in equilibrium vapor pressure due to surface t ension effects at small droplet radii.