Kinematic viscosity of oil

Analyzing the parameters of industrial oil, one often sees reference to “kinematic viscosity of oil”, which raises a question about the difference between viscosity and its kinematic value. Let’s try to understand.

Kinematic viscosity is calculated as the ratio of dynamic viscosity to density. The physical meaning of kinematic viscosity can be shown by the following experiment. Let’s put two equal volumes of liquid into two identical fluid meters, and create equal conditions for leaking. In the event one fluid flows out in 200 seconds, and the other in 400 seconds, it shows that the kinematic viscosity of the 2nd fluid is twice that of the first.

Ease and accuracy of calculating kinematic viscosity  has led it to become an essential parameter in quality control of lubricants.

Also, another important parameter used in this area is viscosity stability, which is the change of viscosity under the influence of operating conditions. The operating conditions for industrial oils are soot pollution, thermal oxidation, shear deformation etc.

Here are the numerical values of the kinematic viscosity of the main types of oils, for comparison:

  • Transformer oil – 24.1 cSt at 70 ° C;
  • Hardening oil  100-120 cSt;
  • Hydraulic oil – from 4.6 to 150 cSt at 40 ° C;
  • Turbine oil – from 20 to 59 cSt at 50 ° C.

These values are approximate. The specific value of kinematic viscosity of oil depends on the manufacturer.