Elemental diffusion and heat transfer coefficients for neutral mixtures under LTE

The phenomena of elemental diffusion is described in detail expressing the elemental fluxes as an explicit function, at constant pressure, of temperature and elemental composition gradients. This study is inspired by the definition of Murphy for elemental combined and thermal diffusion coefficients for mixtures of homonuclear molecules and it is extended to more general mixtures containing hetero-nuclear species. As a direct consequence, the formulation of Butler and Brokaw, for the diffusive transport of species enthalpy, has been generalized introducing both a correction term to the thermal reactive conductivity and the new concept of elemental heat transfer coefficients. These new transport properties are presented both for air and carbon dioxide neutral mixtures suited for Earth and Mars entry applications.