THE SETTLING OF SPHERES IN CLAY SUSPENSIONS

This paper describes the results obtained for a failing ball experiment in opaque aqueous bentonite suspensions. The flow behaviour of the bentonite suspensions has been effectively described by a Bingham flow model which incorporates a yield stress and a plastic viscosity and by a power-law model in terms of an apparent viscosity and a shear rate. A modified particle Reynolds number, based on this power-law model, is formulated for the comparison with the classic drag coefficient correlation derived from the Bingham model and shows the general applicability of the drag coefficient correlation method for non-Newtonian fluids. Both correlations are also compared with the predictions of a finite element method solution based upon a Bingham response. The limitations of the correlation method have been quantitatively addressed to the falling of spheres under dynamic, or incomplete gelatinous, conditions. The wall effect and the influence of the ball surface roughness on the falling sphere characteristics for the same fluid are also described.