Relative viscosity of suspensions of rigid spheres in Newtonian liquids

From viscosity measurements on suspensions of spheres from the literature, the relation between relative viscosity and volume concentration was derived up to 0.5. This relation should be valid at room temperature for rigid smooth spheres, well dispersed without more than loose and random contacts, well wetted, without slip, in aNewtonian low viscous medium of about the same specific gravity, which spheres do not swell nor are electrical charged, whose diameter may vary between e. g. 0,3 and 400μ and whose particle size distribution may be moderately polydisperse. The relation ofηr andc is valid for all rates of shear up toc=0.25 and for sizeable shear rates above that concentration. For higher concentrations the viscosity figures are more uncertain, especially at very low shear rates. The viscosity behaviour abovec=0.5 is still largely unknown. There is still much need for more accurate experimental work on sphere suspensions of varying concentrations at varying rates of shear. There seem to be several critical concentrations, where the flow behaviour shows changes, e. g. atc=0.02–0.07–0.15–0.20 a 0.25–0. 45 −cmax.