Viscosity Calculation The Walther Equation—ASTM

7 Viscosity Calculation The Walther Equation—ASTM D341 

The viscosity of a sample at some temperature can be calculated using the Walther equation if viscosities in centistokes at two other temperatures are available (note this equation holds true only for centistokes measurements). This linear equation is 

This form of the equation has a viscosity scope of 2.0 to 2.0 x 107 and the scope can be expanded down to 0.21 cSt by use of additional coefficients. Details of the method are provided in ASTM D341.30 

For waxy samples, which may be either solid or contain wax crystals at 40°C, it is conventional to measure their viscosities at 65°C (or higher if required) and 100°C and calculate the viscosity at 40°C using ASTM D341 prior to calculating the VI. 

---