Effects of Shear‐thinning Behavior on Mixer Viscometry Techniques3

Brookfield RVTD and HBTD viscometers equipped with a flag impeller, having an impeller‐to‐cup diameter ratio of 0.55, and non‐Newtonian fluids 1.0% guar gum and 1.5, 2.0 and 2.5% carboxymethylcellulose were used to collect torque versus rotational speed 0.5–10.5 rad/s (0.5–100 rpm) data. Power Law consistency coefficient and shear thinning index were quantified using a Haake concentric cylinder viscometer. The proportionality constant which relates mixer shaft speed to effective shear rate (k1) was very sensitive to the shear thinning index at low values of rotational velocity. Results indicate that it is not practical to use one constant value for k1 when measuring properties of shear thinning fluids at low values of N or when using impeller‐to‐cup ratios significantly less than 1.0.