VAPOR FLOWS CAUSED BY EVAPORATION AND CONDENSATION ON 2 PARALLEL PLANE SURFACES - EFFECT OF THE PRESENCE OF A NONCONDENSABLE GAS

A vapor in a gap between two parallel plane surfaces of its condensed phase, on which evaporation or condensation may take place, is conside red in the case where another gas that neither evaporates nor condense s on the surfaces (say, a noncondensable gas) is also contained in the gap. The steady how of the vapor caused by evaporation on one surface and condensation on the other and the behavior of the noncondensable gas are investigated on the basis of kinetic theory. First, fundamenta l features of the how field are clarified for small values of the Knud sen number (associated with vapor-vapor collisions)by a systematic asy mptotic analysis of the Boltzmann equation. Then, the problem is analy zed numerically by means of the direct simulation Monte Carlo method, and the steady behavior of the vapor and of the noncondensable gas (e. g., the spatial distributions of the macroscopic quantities) is clarif ied for a wide range of the Knudsen number. In particular, it is shown that, in the Limit as the Knudsen number tends to zero (the continuum limit with respect to the vapor), there are two different types of th e limiting behavior depending on the amount of the noncondensable gas, and evaporation and condensation can take place only when the average density of the noncondensable gas vanishingly small in comparison wit h that of the vapor. (C) 1998 American Institute of Physics.