(142bu) Correlation Between Radial Filtration and Normal Stress Distribution in Highly Concentrated Suspensions Undergoing Constant-Force Squeeze Flow

Drastic changes in the normal stress distribution in highly concentrated suspensions of non-colloidal spheres in highly-viscous Newtonian fluids undergoing constant-force squeeze flow are explained in terms of the migration of the liquid phase away from the center of the sample. The normal stress is measured using pressure sensitive films, and the solid volume fraction is measured by taking samples from different locations in the sample, dissolving the liquid, and then drying and weighing the solids. Increases in the solid volume fraction near the center cause the normal stress to increase by an order of magnitude in that region and to sharply decrease beyond that.

Changes in the volume fraction of solids due the liquid phase filtration depend on the viscosity of the suspending fluid, the size of the particles, and the initial volume fraction of solids. Under some conditions, the volume fraction of solids remains essentially constant during the squeeze test indicating that liquid phase filtration does not take place to any significant degree; however, under other conditions, the volume fraction of solids increases throughout the sample as the squeezing proceeds and liquid is expelled in preference to the solids. In these latter cases the concentration increases are largest toward the center of the samples. Criteria for the occurrence of the liquid phase migration in suspensions undergoing squeeze flow are presented and discussed.