Apparent viscosity

Apparent viscosity has the SI derived unit Pa·s (Pascal-second), but the centipoise is frequently used in practice: (1 mPa·s = 1 cP).

An apparent viscosity that is reported without the shear rate or information about the instrument and settings (e.g. speed and spindle type for a rotational viscometer) is meaningless.

Multiple measurements of apparent viscosity at different, well-defined shear rates, can give useful information about the non-Newtonian behaviour of a fluid, and allow it to be modeled.

In many non-Newtonian fluids, the shear stress due to viscosity,

has the same sign as du/dy, this is often written as where the term gives the apparent viscosity.

The apparent viscosity of a fluid depends on the shear rate at which it is measured. The apparent viscosity of a dilatant fluid is higher when measured at a higher shear rate ( η 4 is higher than η 3 ), while the apparent viscosity of a Bingham plastic is lower ( η 2 is lower than η 1 ).