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For kinematic viscosity, the SI unit is m^2/s. In engineering, the unit is usually Stoke or centiStoke, with 1 Stoke = 0.0001 m^2/s, and 1 centiStoke = 0.01 Stoke. For liquid, the dynamic viscosity is usually in the range of 0.001 to 1 Pascal-second, or 1 to 1000 centiPoise. The density is usually on the order of 1000 kg/m^3, i.e. that of water.
Kinematic viscosity has units of square feet per second (ft 2 /s) in both the BG and EE systems. Nonstandard units include the reyn (lbf·s/in 2), a British unit of dynamic viscosity. [30] In the automotive industry the viscosity index is used to describe the change of viscosity with temperature.
The poise (symbol P; / p ɔɪ z, p w ɑː z /) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units (CGS). [1] It is named after Jean Léonard Marie Poiseuille (see Hagen–Poiseuille equation). The centipoise (1 cP = 0.01 P) is more commonly used than the poise itself.
By definition, 1 reyn = 1 lb f s in −2.. It follows that the relation between the reyn and the poise is approximately . 1 reyn = 6.89476 × 10 4 P.. In SI units, viscosity is expressed in newton-seconds per square meter, or equivalently in pascal-seconds.
ρ is the density of the fluid (SI units: kg/m 3) u is the flow speed (m/s) L is a characteristic length (m) μ is the dynamic viscosity of the fluid (Pa·s or N·s/m 2 or kg/(m·s)) ν is the kinematic viscosity of the fluid (m 2 /s). The Brezina equation
The poiseuille (symbol Pl) has been proposed as a derived SI unit of dynamic viscosity, [1] named after the French physicist Jean Léonard Marie Poiseuille (1797–1869).. In practice the unit has never been widely accepted and most international standards bodies do not include the poiseuille in their list of units.
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where (in SI units): is the frictional force – known as Stokes' drag – acting on the interface between the fluid and the particle (newtons, kg m s −2); μ (some authors use the symbol η) is the dynamic viscosity (Pascal-seconds, kg m −1 s −1); R is the radius of the spherical object (meters);