Kinetic theory study of steady condensation of a polyatomic gas

The steady one-dimensional flow of a monatomic vapor condensing onto a planar surface kept at constant and uniform temperature has been the subject of a number of investigations based on the kinetic theory of gases. It has been shown that, depending on the upstream value of the Mach number normal to the surface, a steady solution exists only when the problem parameters lie on a surface in the parameters spaces upstream subsonic flow, or when the problem parameters lie in a proper subregion of the whole parameters space upstream supersonic flow. Similar detailed studies do not exist for a polyatomic vapor, in spite of their potential relevance for many applications. The present paper aims at describing the effects of internal degrees of freedom on the relationships which determine the existence of steady one-dimensional condensation flows. The study is based on the numerical solution of the Boltzmann equation for a gas with rotational degrees of freedom. Inelastic collision are described by the Borgnakke-Larsen model. A few cases also have been computed by a finite difference discretization of Holway’s model kinetic equation. The role of boundary conditions is also briefly discussed.