Half-space problem for gas flows with evaporation or condensation on a planar interface with a general boundary condition

Abstract

The half-space problem for steady gas flows with evaporation or condensation is studied for the case where the gas–condensed phase interaction law, i.e., the kinetic boundary condition at the interface between the gas and its condensed phase, is extended to a wide class. It is shown that the half-space problem can be formulated in the form independent of the detail of the generalized kinetic boundary condition concerned. Making use of this fact, we show that the steady solution of the Boltzmann equation with the generalized kinetic boundary condition can be obtained from the steady solution for the complete condensation condition. The conversion formula between the both solutions is derived and the universal functions prescribing the state of the gas at infinity, which are independent of the detail of the kinetic boundary condition, are obtained for the cases of subsonic evaporation and subsonic condensation on the basis of the Boltzmann–Krook–Welander equation.