Apparent and Effective Viscosity of Non-Newtonian Liquids

We have said that for a Newtonian fluid the viscosity can be expressed as shear stress divided by shear rate  

When we consider non-Newtonian liquids, the viscosity is not constant, because of the influence of shear rate and time. So for non-Newtonian fluids we refer to their apparent viscosity (p ), or effective viscosity, and we have to specify the conditions of shear rate to which this applies. When we speak of time-dependent fluids, we must also specify the shear history or kinematic history, at the point that their apparent viscosity is quoted. As long as we keep these restrictions in mind for a non-Newtonian fluid, we can still think of the apparent viscosity as  

That is, the apparent viscosity of a non-Newtonian liquid can be expressed as the ratio of shear stress to shear rate at a specific point within the fluid, and perhaps even at a specific point in time, or within a specific shear-rate range, depending on the nature of the liquid. 

Effective viscosity is a term used to relate non-Newtonian behavior to that of some hypothetical equivalent Newtonian fluid, just as is apparent viscosity. However, the term effective viscosity really relates more to the behavior of the bulk of the fluid and is, as a concept, equal to the Newtonian viscosity that would give the same relationship.  

The units of measurements of apparent viscosity or effective viscosity are the same as those used for viscosity when we refer to a Newtonian fluid. We have mainly used Ib/ft s, which is the unit of viscosity in the fps system. 

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