Question

How to calculate an average viscosity. Give equation for it.

Answer 1

Suppose we have a mixture of two liquids where the kinematic viscosity of one liquid A is ​​ν​a and that of another liquid B is vb, then the average kinematic viscosity of this mixture of liquids is given by the equation:

This equation was proposed by Gambill and is known as Gambill Method.

Another way of calculating the average viscosity of a mixture of liquids is determined by using Refutas equation:
In this method the Viscosity Blending Number (VBN) of each component is calculated using the following formula:

Where vi is the kinematic viscosity of component i.
After calculating this, the VBN of the mixture is calculated for which we have to calculate the average viscosity:

where xi is the mass fraction of component i.
Using the value of VBN of mixture, we can determine the average viscosity of that mixture using the following correlation:

If instead of mass fraction, volume fraction is given, then we use the following formula to determine VBN of each component:

where vi is the kinematic viscosity of component i.
Then VBN of the mixture is given by:

where Vi is the volume fraction of component i.
Therefore the average viscosity of the mixture is given by:

Here exp stands for exponential constant and has the value of 2.718

These are the formulae/ correlation used to determine the average viscosity.