Capillary Diameter Effects on the Apparent Viscosity of the Suspension of Clay Flocs

A flow model consisting of a clear annulus of the suspending layer surrounding a core of the suspension has been proposed for the flow of colloidal suspensions through a capillary tube. In the present study, on the basis of this model, we derived apparent viscosity equations by considering the effects of the slip along the wall of tube and the floc breakup due to shear stress for a coagulated region. The validity of the derived equation was confirmed as follows. For the dispersed region, the derived equation was applied to the experimental data measured by previous authors, in which the apparent viscosity of suspensions of rigid spheres decreased with decreasing capillary diameter. For the coagulated region, the equation was applied to the experimental results obtained by the measurement of apparent viscosity of a montmorillonite suspension. The apparent viscosity decreased with increasing capillary diameter in a region of low electrolyte concentration (0.3, 0.45mol/L NaCl). On the other hand, viscosity decreased with decreasing diameter in a region of high electrolyte concentration (0.8, 1.0mol/L NaCl).