Settling and Interactions of Spheres in Non-Newtonian Fluids

Abstract Settling of particles in both Newtonian and non-Newtonian fluids has been the subject of a number of studies. In Newtonian fluids, the settling process is well understood. The process is less well understood in non-Newtonian fluids. Multiple particle settling in non-Newtonian fluids has not received a great deal of attention, but it is important in a number of industrial processes. In this study, we have examined the behavior of multiple spheres falling in non-Newtonian fluids. For two spheres of different diameters dropped sequentially, we find that the spheres will aggregate and fall together under certain well defined conditions. Both the diameter of the spheres and the rheological properties of the fluid determine settling behavior. Data will be presented for settling of multiple particles (up to five). Interactions between more than two particles settling together are complex. Our experiments indicate that the relationship between settling velocity and the number of the spheres follows some regular pattern. Theoretical work describing the mechanism and conditions under which the two particles with different sizes will settle together in non-Newtonian fluids is also discussed in this paper.