Rheological Behavior of Flocculated and Dispersed Aqueous Kaolin Suspensions in Pipe Flow

Abstract

The flow behavior of both highly flocculated and dispersed kaolin suspensions has been studied using a capillary tube viscometer and two horizontal pipeline test loops. These facilities enabled wall shear rates to be varied from 30 to 11,000 sec−1. Experiments were carried out in which volumetric solids concentrations ranged from 8.6 to 23.4% for the flocculated suspensions, and from 23.4 to 38.7% for the dispersed suspensions. Over the shear rate range 30–1000 sec−1, the rheograms for laminar flow of the flocculated suspensions followed the Ostwald‐de Waele power law model, while for the higher shear rate range 2000–11,000 sec−1, the Bingham plastic model fitted slightly better. Since the high shear rate range was obtained using the capillary tube viscometer, it was concluded that great care must be exercised when scaling up from capillary tube data to pipeline installations, in which the wall shear rate rarely exceeds 500 sec−1. The dispersed kaolin suspensions were essentially Newtonian, but at the highest solids concentration a measurable degree of shear‐thickening behavior was observed. Results for turbulent flow of the flocculated material are in good agreement with those obtained for similar systems by Kemblowski and Kolodziejski (1973), who have already shown that Dodge and Metzner's equation (1959) for the friction factor of a power law material is not applicable.