The inelastic contributions to transport collision integrals in the infinite-order sudden approximation

Abstract

The transport collision integrals of the Wang Chang and Uhlenbeck kinetic theory of polyatomic gases have been evaluated for an anisotropic intermolecular pair potential model for the He-CO₂ interaction. The calculations have made use of the infinite-order sudden approximation to evaluate the state-to-state differential cross-sections, but otherwise involve no approximations.

The results indicate that some earlier approximate methods for the evaluation of the collision integrals are quantiatively correct, although they are given a new interpretation. In particular, the simplifications introduced by Mason and Monchick are shown to yield essentially the same collision integral for viscosity as the more exact treatment. On the other hand, several long established procedures for treating the transport properties of polyatomic gases and gas mixtures are shown to be significantly in error. Specifically the diffusion coefficient for internal energy is some 10 per cent higher than the diffusion coefficient for mass, and the latter itself quite different from that obtained on the basis of the treatment of Monchick and Mason.