2 SIMPLE APPROXIMATIONS TO THE THERMAL-DIFFUSION FACTOR AND THEIR APPLICATIONS TO FLAME STUDIES

It is shown that formulas developed previously for the thermal diffusion factor imply a close relation between it and the translational and internal heat conductivities, lambda //i//t//r//a//n//s and lambda //i//i//n//t, of each species in a multicomponent mixture. This suggests a phenomenological relationship that is more difficult to calculate than the translational heat conductivity of a multicomponent mixture. The calculation in fact uses the same set of inputs and collision integrals that enter the calculation of lambda //i//t//r//a//n//s and seems to be as accurate as the first Chapman-Cowling approximation of alpha //i//j. Further approximations lead to a 'back-of-the-envelope' approximation for the high-temperature limit. Coupled with the binary trace approximation, this allows extremely fast estimates of thermal diffusion fluxes.