ORDINARY AND THERMAL DIFFUSIONS IN POLYATOMIC BINARY-FLUID MIXTURES

General formulas for the ordinary and Soret diffusion coefficients D-1 2 and D-T, and the thermal-diffusion ratio kr (or the thermal-diffusio n factor alpha(12)) of a binary and dilute fluid mixture consisting of nonspherical molecules have been obtained utilizing the classical tra nsport theory recently developed by us [G. S. Singh and B. Kumar, J. C hem. Phys. 104, 5604 (1996)]. The general results involve up to the in finite order of approximations but in the present work we have restric ted ourselves up to the second order only. We thus obtain general expr essions for the second approximation to both D-12 and D-T, and the fir st approximation to k(T) (or alpha(12)) in terms of different square b racket integrals. The velocity as well as angular velocity parts of th ese integrals for the fluid mixtures of hard biaxial ellipsoids have b een analytically performed with the help of the modified Hoffman proce dure. The expressions for [D-12]2, [D-T](2), and [k(T)](1) have thus u ltimately been obtained in terms of five four-dimensional quadratures over the orientational coordinates of like or unlike pairs of collidin g ellipsoidal molecules. (C) 1998 American Institute of Physics.