Mass and entropy transport in a suspension of rigid particles

Abstract

Mass and entropy transport in a suspension are analysed in the framework of irreversible thermodynamics. Our approach extends the one used by Einstein and Batchelor for the study of Brownian diffusion. We show that the well-known coupling (due to the Onsager symmetry relations) which occurs in a two-component mixture, also occurs in a two-phase suspension, as a consequence of the joint role played by the relative velocity in mass and entropy transport. Most noticeable results are i) if the suspended particles are rigid, surface tension cannot lead to any thermo-diffusion (Soret effect); ii) the general expression for the diffusion constant depends on the densities of the two phases; iii) in a rotating suspension, the Coriolis force acting on the relative motion is not the one commonly found in the literature and iv) diffusion by non-homogeneous velocity gradients (Faxen's diffusion) may become important whenever sedimentation is negligible En utilisant la thermodynamique des phenomenes irreversibles, on fait une analyse du transport de masse et d'entropie dans une suspension. La methode utilisee est une extension de celle appliquee par Einstein et Batchelor a l'etude de la diffusion brownienne