The sedimentation of suspensions of spheres

An experimental investigation of Hawksley's equation for the sedimentation of suspensions of spheres has shown close agreement with the theory, except that the derived value of Einstein's viscosity constant appears to vary with the size range, possibly exceeding 3.4 for equi-sized spheres. When spheres of the same density as the sedimentary fluid were added to the suspension, a slight decrease in settling rate was produced at total volume concentrations not exceeding about 10%. Above this figure, appreciable increases in settling rate were found and were attributed to hydrodynamic attractive-forces between the spheres leading to the development of vertical streams in the suspension.