A Mixer Viscometry Approach to Use Vane Tools as Steady Shear Rheological Attachments

Abstract

A mixer viscometry procedure, coined the Matching Stress Method, was developed to use four-bladed vanes devices in applications requiring steady shear measurements. Based on the concept that vane tools shear fluids in a cylindrical pattern defined by their geometry, this technique determined a mixer viscometry constant to predict average shear rates for vanes. Three cylindrical bobs and three, four-bladed vanes were used to investigate the impact of attachment geometry on the mixer viscometry constant. Two Newtonian fluid standards and three carboxy-methyl-cellulose (CMC) solutions were used to examine fluids with varying rheological properties. Four cups of varying dimensions contained the sample fluids and provided a system of fluid gaps for comparison. A Bohlin VOR Rheometer collected torque and angular velocity data for vane and bob attachments. For the bob devices, torque and angular velocity measurements were converted into shear stress and shear rate rheograms. Torque responses collected using the vanes were converted into shear stress measurements, and the proposed method matched the vane rheograms with each bob of identical height, diameter, and corresponding system geometry. Variation of system geometry and flow properties revealed the mixer constant depended on fluid gap size when below a cup-to-vane diameter ratio of 2.1 and a flow behavior index of 0.86. This procedure enables vane tools to be used in steady shear applications, not limiting their employment to single point, yield stress determination.

Keywords

• vanes
• steady shear rheology
• mixer viscometry