Evaluating Shear Rates for Power Law Fluids in Mixer Viscometry

Established mixer viscometry methods, the viscosity matching and the slope methods, were evaluated for determining average shear rates when agitating time‐independent, non‐Newtonian fluids. Results indicate that the use of a constant value of the mixer proportionally constant, k ', is not valid for all ranges of fluid rheological properties, system geometry (impeller and cup) and impeller rotational speed. A small impeller‐to‐cup diameter ratio and impeller rotational speeds greater than .33 rev/s (20 rpm) provide the optimum operating parameters for evaluation of k '.