The extension viscosity model describes the dependence of the viscosity on the shear rate, temperature, pressure, and extension rate in 3D flow. The extension viscosity coefficients are determined by using the shear viscosity model and experimental pressure measurements in convergent flow.
The extension viscosity model is given by the following equation:
where:
-
-
is the unified viscosity (Pa.sec.) -
is the shear viscosity (Pa.sec.) -
is the temperature (K) -
is the pressure (Pa) -
is the shear rate (1/sec.) -
is the extension rate (1/sec.) -
and 
and are data-fitted coefficients
The coefficient reflects the importance of extension stresses. The extension stress makes no contribution to the viscosity when the value of is zero. Valid ranges for are: Min=0, Max=1e7, Typical=10.
The coefficient reflects the extension rate of the transition to strong extension stresses. Valid ranges for are: Min=0, Max=1e7, Typical=500.