From Molecular Mixtures to Suspensions of Particles

(Received 3 June 1994, accepted in final form 10 October 1994)

Abstract
Some extensions of the model of molecular mixtures have already appeared which aim at describing suspensions of particles with supramolecular sizes. These models present some deficiencies that can be traced partly to the assumed expressions for the momentum and energy fluxes, and partly to their discarding of a very important physical phenomenon: the flow-induced velocity fluctuations that exist in an otherwise laminar suspension. We here propose a new phenomenological description of suspensions. The approach is mainly macroscopic, but each flux or transport coefficient is carefully defined in terms of statistical averages. Among other topics, we analyse the thermal diffusion (Soret effect) in a suspension and emphasize the role of velocity fluctuations in the average motion of the particles.