(556f) Mixing of Yield Stress Fluids

Yield stress fluids are commonly encountered in several industries including paints, sealants and adhesives, food and personal products. Often the product is formulated so that it exhibits a yield stress to give properties that are desirable to the customer.

Agitation equipment must generate a shear stress that is greater than the fluid’s yield stress before it moves. If the stress is less than the yield stress stagnant regions will form in the vessel.

This presentation will review the definition of viscosity, how it is measured and how rheology data are analyzed to determine how to mathematically describe these fluid properties.

Then the issues associated with the measurement of yield stress will be addressed and the design of agitators, using the rheological model, will be discussed.

The presentation will end with two real examples of sizing agitators for processing yield stress fluids.