Notes on the boundary conditions for fluid-dynamic equations on the interface of a gas and its condensed phase

The Boltzmann equation was used to study the boundary conditions of fluid-dynamic equations at the interface of a gas and its condensed phase. The study was based on the conservation laws and the H-theorem. Numerical results proved that the solution of half-space supersonic condensation problem existed only in a limited range of parameters of the problem and this was supported by the bound on the supersonic condensing boundary. The results were applied to the boundary value problem of evaporation and condensation and the direction of flow on which boundary evaporation occurred was also discussed.