Relaxation Effects in the Transport Properties of a Gas of Rough Spheres

Abstract

The rough-sphere model is investigated in some detail from the point of view of the formal kinetic theory of polyatomic molecules developed by Wang Chang and Uhlenbeck, and by Taxman. The purpose is to clarify the sources of some discrepancies between the known results for the transport properties of a rough-sphere gas and the results recently obtained by Mason and Monchick in an approximate treatment of the formal kinetic theory, in which the corrections for inelastic collisions are given in terms of relaxation times. It is found that the deviations of the transport coefficients of rough spheres from those of smooth spheres can be understood in first approximation as the result of two effects: an enhancement of the backward and sideward scattering of rough spheres over that for smooth spheres, and an apparent resonant exchange of internal energy when two rough spheres collide. Since these effects are, for the most part, peculiar to rough spheres, it is concluded that the deviations found between the rough-sphere model and the approximate theory are not to be expected for real molecules.