The following methods are used by CHEMCAD for the calculation of vapor viscosity. The DIPPRmethod is the default.
1. DIPPR Library equation
2. Chapman-Enskog (for low pressure gases)
a. Neufield method for collision integral
b. Brokaw method for collision integral
3. Method of Thodos
Note that the default method for a simulation can be changed. Go to the thermophysical menu and select transport properties to change the default method.
For low pressure gas, the Chapman-Enskog relation is used: