11/23/2023 1 Comment Kinematic viscosity of water at 10 c![]() The kinematic viscosity in cSt at 40☌ is the basis for the ISO 3448 kinematic viscosity grading system, making it the international standard. Several engineering units are used to express viscosity, but the most common by far are centistoke (cSt) for kinematic viscosity and the centipoise (cP) for dynamic (absolute) viscosity. Typically, viscosity is reported at 40☌ and/or 100☌ or both if the viscosity index is required. The temperature must be defined to interpret the viscosity reading. Likewise, reporting viscosity for trending purposes without a reference to temperature is nonsensical. Viscosity is not a dimensional measurement, so calling highly viscous oil thick and less viscous oil thin is misleading. Sometimes, viscosity is erroneously referred to as thickness (or weight). Generally speaking, viscosity is a fluid’s resistance to flow (shear stress) at a given temperature. Given the importance of viscosity analysis coupled with the increasing popularity of onsite oil analysis instruments used to screen and supplement offsite laboratory oil analysis, it is essential that oil analysts understand the difference between dynamic and kinematic viscosity measurements. ![]() By contrast, most onsite viscometers measure dynamic viscosity, but are programmed to estimate and report kinematic viscosity, so that the viscosity measurements reported reflect kinematic numbers reported by most labs and lube oil suppliers. Most used oil analysis laboratories measure and report kinematic viscosity. The two are easily confused, but are significantly different. Viscosity can be measured and reported as dynamic (absolute) viscosity or as kinematic viscosity. However, there is more to viscosity than meets the eye. Likewise, there is no property more critical to effective component lubrication than base oil viscosity. Of all the tests employed for used oil analysis, none provides better test repeatability or consistency than viscosity. Viscosity reporting is only valid when the temperature at which the test was conducted also is reported - for example 23 cSt at 40 degrees C. This value is converted to standard units such as centistokes (cSt) or square millimeters per second. It is determined by measuring the time in seconds, required for a fixed volume of fluid to flow a known distance by gravity through a capillary within a calibrated viscometer at a closely controlled temperature. The conversion of conventional measures into cSt is inaccurate, particularly within the 1 to 9.5 cSt range (see DIN 1342, viscosity of NEWTONian liquids).Kinematic viscosity is a measure of a fluid's internal resistance to flow under gravitational forces. If values higher than 1000 cSt are required, the data given from 60 cSt can be multiplied accordingly by 10, 100, 1000 etc. The table can also alternatively be used to assign corresponding values to one another. The former units are no longer approved and can be converted to m²/s using Fig. To ensure correct usage, the Stokes units and the units still currently in general use must be converted into the SI unit m 2/s. These are: degrees Engler (✮) in Germany, Saybolt seconds (S˝) in USA and Redwood seconds (R˝) in Britain. The conventional units of viscosity are unsuitable as a basis for calculation, but are still used in commerce. The Stokes unit ceased to be officially valid in 1978. The hundredth part thereof is a Centi stokes (cSt). The unit used here is m 2/s and is called – in honour of the Irish physicist STOKES – a Stokes (St). However, most measurements are still made in centistokes, e.g. Thus water at 20 ✬ has a kinematic viscosity ν = 1,002 ![]() Kinematic viscosity (ν) designates the quotient of the dynamic viscosity of the fluid handled and its density.
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