Correlation of dense fluid self-diffusion, shear viscosity, and thermal conductivity coefficients

Abstract

A general procedure has been developed for simultaneously fitting any two of the self-diffusion coefficient, the viscosity (as the fluidity), and the thermal conductivity (as its reciprocal) as Dymond reduced coefficients, (D*,η*,λ*), to a simple function of the volume and the temperature for dense fluids. For example,D*=ζ₁+ζ₂ V _r/(1+ζ₃,/V _r), whereV _r=V[1-ζ₁(T−T _r)-ζ₂(T−T _r)²].T _r is any convenient temperature, here 273.15 K. AsV _r is common to the two properties, only eight coefficients, ζ_j and ζ_k are required. Such reduced transport-coefficient curves are geometrically similar for members of groups of closely related compounds. The procedure has been extended to give “family” curves for such groups by fitting a pair of transport properties for three substances from the group in a single regression. Overall, fewer coefficients are required than for other schemes in the literature, and the fitting functions used are simpler. The curves so constructed can be used for the correlation of data obtained from different sources, as well as interpolation and, to a limited extent, extrapolation. A comparison is made for a number of compotmd groups between simultaneous fits of the pairs (D−η ), (D−λ), and (η−λ)