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Friday, 1 December 2017


We were discussing the basic definition and significance of fluid mechanics and various properties of fluid in our previous post. 

Now we will understand here the term “Kinematic Viscosity” of fluid with the help of this post.

Kinematic Viscosity

Before going to discuss the term Kinematic Viscosity, we must remind here the basic definition of viscosity or dynamic viscosity.

Viscosity or dynamic viscosity is basically defined as the resistance provided to a layer of fluid when it will move over another layer of fluid. For complete information about the fluid viscosity, please find the respective post “Basic definition of viscosity”.

Kinematic viscosity of fluid is basically defined as the ratio of dynamic viscosity to the density of fluid.

Kinematic viscosity = Dynamic viscosity / Density of viscosity
ν = μ/ρ

Unit of kinematic viscosity

Unit of kinematic viscosity in S.I system will be m2/s
Unit of kinematic viscosity in C.G.S system will be stokes or cm2/s
Unit of kinematic viscosity in F.P.S system will be inch2/s
1 Stokes = 10-4 m2/s

Viscosity sensitivity to temperature will be expressed in the terms of viscosity index and this is a dimensionless number. Viscosity index will be provided in the range of 0 to 100 to indicate the temperature sensitivity for given fluid.

Viscosity index 100 indicates the least temperature sensitive oil and Viscosity index 0 indicates the most temperature sensitive oil. Viscosity index could be increased above 100 with addition of some additives.

Let us see here the dynamic viscosity and kinematic viscosity for water and air at standard atmospheric pressure with the help of following table.

We will now discuss the types of fluids in the category of fluid mechanics in our next post.
Do you have suggestions? Please write in comment box.


Fluid mechanics by Y. Nakayama and R F Boucher
Image Courtesy: Google

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