Viscosity Measurements in the Presence of Wall Slip in Capillary, Couette, And Parallei-Disk Geometries

Abstract

Summary: Measurements of viscosities for slurries, cements, gels, foams, and emulsions are often confounded by the presence of slip at solid boundaries. Slip arises from thin regions of low-viscosity fluid at the boundary that result in large velocity gradients near the solid surface. Unless the measurements are corrected for slip, the calculated viscosities will be smaller than the true fluid viscosities. We review available techniques for determining wall slip velocities and viscosities in standard geometries. The earlier techniques of Mooney for capillaries and Couette geometries are presented. In addition, new analyses are presented for Couette and parallel-disk geometries. The new Couette analysis requires only two measurements rather than the three required in Mooney's analysis. Examples showing the application of these techniques are given for the capillary, Couette, and parallel-plate geometries. Experimental techniques to eliminate wall slip by use of rough surfaces are described.