Approximate Theory of Transport in Simple Dense Fluid Mixtures

The theory of transport proposed by Rice and Kirkwood is extended to the case of multicomponent systems. As in the previous case, the intermolecular force contributions to the shear and bulk viscosities and the thermal conductance are displayed as functions of the diffusion coefficient and the thermodynamic properties of the mixture. The self-diffusion coefficient is related to the intermolecular forces and molecular distribution function, thereby completing the molecular basis of the computation. Formulas are also given for the thermal diffusion factor and the heat of transport. The reader is referred to Eqs. (91), (104), (106), and (109). The theory presented predicts a form of volume fraction mixing. For example, the shear viscosity becomes η=(ν1*/ν)2η1*+(ν2*/ν)2η2*+2(ν1*ν2*/ν2)η12*,with v1* and v2* the volume of N1 molecules of component one and of N2 molecules of component two, respectively, at the same temperature and pressure as the mixture. The quantities η1*, η2*, η12* are composition dependent so that the predicted mixing law is not pure volume fraction mixing except in the case of an ideal solution. The theory is compared with experimental measurements of the viscosity of benzene—carbon tetrachloride mixtures, and good agreement is found. The agreement between theory and experiment is discussed with reference to the mechanism of irreversibility.

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