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The power law exponent is obtained from Equation 1.37
Using the values for A0, A v and so on
n = 3.196
1.3.7.4 Carreau's Viscosity Equation [11]
As shown in Figure 1.14 [12], the Carreau equation provides the best fit for the viscosity
function, reproducing the asymptotic form of the plot at high and low shear rates correctly.
The equation is expressed as
(1.38)
where A, B, C are resin-dependent constants. By introducing the shift factor aT into
Equation 1.38, the temperature-invariant form of the Carreau equation can be given as
(1.39)
For a number of resins the shift factor can be calculated as a function of temperature
from the following equation with good approximation [9,10]
(1.40)
where T1 ( 0 C) is the temperature at which the viscosity is given and T2 ( 0 C) the temperature
at which the viscosity is calculated.
The standard temperature TST is given by [9]
TST=Tg +50 0 C (1.41)
Viscosity 7?
Vo=*
Shear rate f
/=1/B
Slope: -C
Figure 1.14 Determination of Carreau-parameters from a viscosity function [12]