| This thesis describes the experimental and theoretical investigation of three different problems, two of which involve the flow of concentrated suspensions undergoing shear and the third relates to rimming flows of viscous particle-free liquids within a partially filled rotating horizontal cylinder. The first deals with the viscous resuspension of heavy particles in a varying shear flow field, where the particles, although heavier than the suspending fluid, are resuspended due to the action of shear induced migration. Here, under fully developed flow conditions, we measured the resuspension height, the cup-mixing particle concentration and the velocity profiles across the pipe's cross section. These results were then compared to those computed using a theoretical model based on the theory of shear induced migration (Leighton & Acrivos [1]), as done by Zhang & Acrivos ([2]). Although qualitatively in agreement, quantitative differences were found between the experimental results and the model predictions. The second problem deals with a curious and as yet unexplained phenomenon of particle segregation into regions of high and low concentration in a neutrally buoyant suspension undergoing shear in the presence of a free surface. Here experiments were performed in two different geometries, viz. a partially filled horizontal Couette device and a partially filled rotating horizontal cylinder. Although it seems likely that the particle segregation phenomenon observed in both the geometries is initiated by particle concentration fluctuations which, in turn, lead to fluctuations in the effective viscosity of the suspension, we have been unable to provide a quantitative explanation for this observation. Finally, the particle segregation experiments motivated us to investigate theoretically the flow of a viscous particle-free liquid in a partially filled rotating horizontal cylinder. We found that, under creeping flow conditions, the addition of the hydrostatic pressure term to the standard lubrication equation leads to film thickness profiles which, over a broad range of parameters, are in close agreement with those obtained experimentally, as well as via the solution to the full Stokes equations. |
