Viscous resuspension in a bidensity suspension

Experiments were performed in a narrow gap Couette device to study the viscous resuspension process in a bidensity suspension consisting of two types of spherical particles, both having the same size, one of which was heavy, while the other had the same density as that of the suspending fluid. The resuspension height of an initially settled bed of heavy particles was measured over a ten-fold range of applied shear rates, using an imaging technique which was developed to study the particle migration process in concentrate bidisperse suspensions. It was found that, at a given shear rate, the resuspension height of the heavy particles increased with an increase in the concentration of the neutrally buoyant spheres. The experimental results were then compared with the predictions of a bidensity model based on the particle migration theory of previous work, and good agreement was found between the two. (C) 1999 Elsevier Science Ltd. All rights reserved.