Effect of polydispersity on hydrodynamic diffusion coefficient in sedimentation process

Abstract

In sedimentation of non-colloidal particles three effects-hindered settling, polydispersity, and hydrodynamic diffusion-play important roles in determining the behavior of the interface region. In order to estimate the diffusion coeffcient for hydrodynamic interaction, the volume fraction of the particles is measured by using NMR-CT, and the mass conservation equation is employed as the model equation, in which only the hindered settling and the hydrodynamic diffusion are taken ito account. The polydispersity effect is eliminated by the extrapolation of the apparent diffusion coefficients to zero time. The diffusion coefficient at time zero, which is purely due to hydrodynamic interaction, increases with increasing bulk volume fraction of particles until it shows maximum at the bulk volume fraction 0.05, and decreases rapidly with the bulk volume fraction up to 0.2.