Mixing of Viscous, Non-Newtonian Fluids

Many viscous fluids processed in industry exhibit non-Newtonian rheology. These industries include paints, personal products such as shampoo and detergents and food products such as ketchup and mayonnaise. All at some stage in their production require mixing. Most of these fluids are shear-thinning which means that the apparent viscosity of the fluid will be low near the impeller, where velocity gradients are high, and high near the vessel wall where velocity gradients are low. This presentation will discuss how to select the impeller type that is appropriate for a particular operating regime (Reynolds number). Then correlations for estimating blend times in Newtonian fluids will be discussed and how they can be modified to take account of non-Newtonian fluid behavior. There is a class of fluids which exhibit a yield stress, meaning that a minimum level of shear must be applied before the fluid will move. Examples include toothpaste and high solids loading slurries. The rules used to size mixing equipment for these fluids will be discussed.