Mixing and Viscosity Determinations with Helical Ribbon Impeller

L. Slemenik Perše and M. Žumer

Abstract
Fluids with complex rheological properties often exhibit shear dependence and/or time dependence. Due to high viscosity and complex rheological behavior, mixing of such fluids is usually performed in the laminar flow regime. The object of this work was to study the mixing of highly viscous and rheologically complex fluids with single-flight helical ribbon impeller. Highly viscous motor oils were used as Newtonian fluids, while two different types of non-Newtonian fluids were used. Carboxymethyl cellulose represented well-known shear thinning non-Newtonian fluid, and welan solutions represented rheologically complex and more structured non-Newtonian fluid. Torque was measured at different impeller speeds in order to obtain power curves and to calculate viscosity of different non-Newtonian fluids as a function of impeller speed. The results of the mixing study of different highly viscous fluids showed that the torque depended on the impeller speed and the rheological properties of the fluid. Shear rate constant Ks was determined for non-Newtonian fluids with different rheological properties and it was shown that Ks depends on fluids properties. The comparison between mixing experiments and rheological measurements showed that the shear-dependent viscosity could be determined during the mixing process by measuring the torque on the impeller.

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Keywords
Mixing, rheology, carboxymethyl cellulose, welan, helical ribbon impeller