
If you are modeling a problem that involves heat transfer, you can define the viscosity as a function of temperature . Five types of functions are available:
(8.42)  
(8.43) 

The power law described here is different from the nonNewtonian power law described in Section
8.4.5.

For one of the first three, select piecewiselinear, piecewisepolynomial, polynomial in the Viscosity dropdown list and then enter the data pairs ( ), ranges and coefficients, or coefficients that describe these functions Section 8.2. For Sutherland's law or the power law, choose sutherland or powerlaw respectively in the dropdown list and enter the parameters.
Sutherland Viscosity Law
Sutherland's viscosity law resulted from a kinetic theory by Sutherland (1893) using an idealized intermolecularforce potential. The formula is specified using two or three coefficients.
Sutherland's law with two coefficients has the form
where,
=  the viscosity in kg/ms  
=  the static temperature in K  
and  =  the coefficients 
=  the mass fraction of species  
=  the molecular weight of species  
=  the Operating Pressure 
For air at moderate temperatures and pressures, kg/msK , and K.
Sutherland's law with three coefficients has the form
where,
=  the viscosity in kg/ms  
=  the static temperature in K  
=  reference value in kg/ms  
=  reference temperature in K  
=  an effective temperature in K (Sutherland constant) 
For air at moderate temperatures and pressures, kg/ms, = 273.11 K, and = 110.56 K.
Inputs for Sutherland's Law
To use Sutherland's law, choose sutherland in the dropdown list to the right of Viscosity. The Sutherland Law panel will open, and you can enter the coefficients as follows:

Use SI units if you choose the twocoefficient method.

PowerLaw Viscosity Law
Another common approximation for the viscosity of dilute gases is the powerlaw form. For dilute gases at moderate temperatures, this form is considered to be slightly less accurate than Sutherland's law.
A powerlaw viscosity law with two coefficients has the form
where is the viscosity in kg/ms, is the static temperature in K, and is a dimensional coefficient. For air at moderate temperatures and pressures, , and .
A powerlaw viscosity law with three coefficients has the form
where is the viscosity in kg/ms, is the static temperature in K, is a reference value in K, is a reference value in kg/ms. For air at moderate temperatures and pressures, kg/ms, K, and .

The nonNewtonian power law for viscosity is described in Section
8.4.5.

Inputs for the Power Law
To use the power law, choose powerlaw in the dropdown list to the right of Viscosity. The Power Law panel will open, and you can enter the coefficients as follows:

Note that you must use SI units if you choose the twocoefficient method.
