DSMC MODELING OF INTERFACE CURVATURE EFFECTS ON NEAR-INTERFACE TRANSPORT

This paper summarizes results of an investigation of surface tension and interface curvature effects on transport near the interface of droplet embryos formed by nucleation in a supersaturated gas mixture. Immediately after nucleation, 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 non-continuum transport effects, and (2) surface tension and interface curvature effects may strongly alter the transport at the interface of the droplet. In the study reported here, a direct simulation Monte Carlo (DSMC) 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 non-condensable gas. The simulation method used in this study is similar to that used by Carey et al. [1], incorporating modifications to account for condensation and to allow determination of the initially unknown temperature at the droplet surface. In the simulation, the boundary condition at the droplet surface is treated in a manner that models the combined effects of interfacial tension and interface curvature on transport. Results of the calculations are compared with growth rates inferred from the data of Peters and Paikert [2]. The simulation results indicate that surface tension and curvature effects play significant roles 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.