Mass-Transfer Coefficients in Dense Binary Mixtures

A modified elementary kinetic theory of gases is generalized to arbitrary densities of mixtures (from the gaseous to the solid state). Derived expressions for the mass-transfer coefficients are based on the lattice gas model, which is applicable to all the three aggregation states. For a rarefied gas, the expression for the mutual diffusion coefficient that is derived in terms of the modified theory is consistent with that obtained in terms of the rigorous kinetic theory of gases. The migration of particles is described in terms of transition state theory. The theory takes into account the role of thermal fluctuations in surmounting the activation barrier in dense phases. The label diffusion coefficient, pressure diffusion coefficient, thermal diffusion coefficient, and forced diffusion coefficient are discussed.