Condensation Droplet Growth in Rarefied Gases

摘要

An analysis is made of thermal and diffusion effects on the droplet growth phenomena in a supersaturated vapor and inert carrier gas (see also AD-646 669). Two cases are considered: 1) constant fluid conditions, and 2) changing fluid conditions due to condensation effects. The analysis is so formulated as to describe the continuous growth process as the droplet size increases from microscopic (free-molecular) to 'rarefied', even to macroscopic (continuum). Equations for the conservation of mass and energy are derived by application of the 'Langmuir model' in the rarefied ('slip') regime and two correlation parameters for the mass transfer and the energy transfer are introduced for analyzing this regime. Analytic solutions are obtained for the droplet growth with time by expressing the saturation vapor pressure as a linear function of temperature. The results indicate that the choice of these slip-regime parameters influence the droplet growth only when the ratio of the droplet size to the mean free path is of order one. However, when the droplet size is very small or very large compared to the mean free path, the values chosen for these parameters have a negligible effect on the droplet growth. (Author)