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where U is the oil's kinematic viscosity at 40 °C (104 °F), Y is the oil's kinematic viscosity at 100 °C (212 °F), and L and H are the viscosities at 40 °C for two hypothetical oils of VI 0 and 100 respectively, having the same viscosity at 100 °C as the oil whose VI we are trying to determine.
The proportionality factor is the dynamic viscosity of the fluid, often simply referred to as the viscosity. It is denoted by the Greek letter mu ( μ ). The dynamic viscosity has the dimensions ( m a s s / l e n g t h ) / t i m e {\displaystyle \mathrm {(mass/length)/time} } , therefore resulting in the SI units and the derived units :
Consequently, if a liquid has dynamic viscosity of n centiPoise, and its density is not too different from that of water, then its kinematic viscosity is around n centiStokes. For gas, the dynamic viscosity is usually in the range of 10 to 20 microPascal-seconds, or 0.01 to 0.02 centiPoise. The density is usually on the order of 0.5 to 5 kg/m^3.
One can convert efflux time to kinematic viscosity by using an equation for each cup specification number, where t is the efflux time and ν is the kinematic viscosity in centistokes. Zahn Cup #1: ν = 1.1( t − 29)
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
The criteria were reformulated in 1967 to use kinematic viscosity in centiStokes and the cold-cranking simulator. The 15W grade was added December 1975. [11] [19] In 1980, 0W and 25W grades were added, and a low-temperature pumpability test. Grade 60 was re-added in 1987. HTHS viscosity was added in 1992. [19] Grade 16 was added in 2013.
This measured kinematic viscosity is generally expressed in seconds of flow time which can be converted into centistokes (cSt) using a viscosity calculator. [ 2 ] Flow cups are manufactured using high grade aluminium alloy with stainless steel orifices (where indicated), flow cups are available with a range of UKAS / ISO 17025 certified ...
The grades include single grades, such as SAE 30, and also multi-grades such as SAE 15W-30. A multi-grade consists of a winter grade specifying the viscosity at cold temperatures and a non-winter grade specifying the viscosity at operating temperatures. An engine oil using a polymeric viscosity index improver (VII) must be classified as multi ...