Kinetic Theory of Transient Condensation and Evaporation at a Plane Surface

The phenomenon of transient condensation onto, or evaporation from, a liquid sheet in contact with its pure vapor is treated from a kinetic theory viewpoint. The Maxwell moment method is used to formulate the detailed transient problem. A steady surface mass flux rate exists for times large in comparison with the collision time, that is, in the continuum regime, and explicit formulas are given for this limit. The complete gasdynamic field, however, is nonsteady for all times. The calculations are carried out utilizing four moments, and the effects of incorporating additional moments are negligible. Finally, the analysis is extended to incorporate imperfect mass and temperature accommodation. Examination of the transient solution and a matched asymptotic "quasisteady" solution shows that the gasdynamic field consists of a diffusion process near the liquid surface coupled through an expansion or compression wave to the constant far field state