Kinematic viscosity/ momentum diffusivity:
- It is defined as the ratio of dynamic viscosity to the density of the fluid.
ν = μ / ρ
where
ν = kinematic viscosity (m2/s)
μ = absolute or dynamic viscosity (N s/m2)
ρ = density (kg/m3)
In the SI-system the theoretical unit of kinematic viscosity is m2/s - or the commonly used Stoke (St) where
- 1 St (Stokes) = 10-4 m2/s = 1 cm2/s
Stoke comes from the CGS (Centimetre Gram Second) unit system.
Since the Stoke is a large unit it is often divided by 100 into the smaller unit centiStoke (cSt) - where
- 1 St = 100 cSt
- 1 cSt (centiStoke) = 10-6 m2/s = 1 mm2/s
- 1 m2/s = 106 centiStokes
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