Measurement of the kinematic viscosity
Measurement of the viscosity of the kinematic of fluids
If Newtonian liquids are tested with capillary viscometers, the viscosity is expressed in units of kinematic viscosity. Gravity is used as the force driving the liquid through the capillary. The density of the sample is an additional parameter.
Kinematic viscosity and dynamic viscosity are related by the following formula:
ν=η/ρ (m²/s) with
ν = viscosité cinématique en m²/s,
η = viscosité dynamique en Pa.s
and
ρ = masse volumique en kg/m3
Kinematic viscosity was previously expressed in “stokes” [St] or “centistokes” [cSt].
1 cSt = 1 mm²/s = 10-6 m²/s knowing that 1St = 100 cSt
For a liquid of density close to 1000kg/m3 (density = 1), we can make the following approximation: 1cSt = 1cP (see dynamic viscosity).
Note: The values “Ford Cup seconds”, “Engler Degrees”, “Saybolt or Redwood seconds” are only relative viscosity values which, for non-Newtonian liquids, cannot be converted into absolute viscosity values η or ν.
