![]() Dynamic viscosity is sometimes referred to as absolute viscosity, or just viscosity, while Kinematic viscosity is sometimes called the diffusivity of momentum. In a cgs unit system, dynamic viscosity is in a unit called ‘poise’, which is taken from the name of Jean Louis Marie Poiseuille, while Kinematic viscosity is expressed in ‘stokes’ (St) or centistokes (ctsk or cSt), which are named after George Gabriel Stokes.Ĥ. Dynamic viscosity is symbolized by either ‘µ’ or ‘n’, while Kinematic viscosity is mathematically symbolized by ‘v’.ģ. Dynamic viscosity is the quantitative expression of fluid’s resistance to flow, while Kinematic viscosity is the ratio of the fluid’s viscous force to the inertial force.Ģ. Therefore, it is used in dimensionless numbers, which compares the ratio of the diffusivities.ġ. Kinematic viscosity is sometimes called the diffusivity of momentum, due to the fact that it has the same unit when compared to the diffusivity of mass and diffusivity of heat. It should be noted that water (H2O) at 20 degrees centigrade is about 1 cSt. Kinematic viscosity is also expressed in stokes (St) or centistokes (ctsk or cSt), for cgs units. The first is dynamic viscosity, also known as absolute viscosity, which measures a fluid’s resistance to flow. Kinematic viscosity is mathematically defined as:įor SI units, it is expressed as m^2/s. Kinematic viscosity is symbolized by the Greek letter nu (v). Inertial force is characterized by fluid density (p). Kinematic viscosity, on the other hand, is a ratio of the viscous force to the inertial force. However, the most common expression is centipoise (cP), which is mainly used in ASTM standards. For cgs, dynamic viscosity is in a unit called ‘poise’, which is taken from the name of Jean Louis Marie Poiseuille. Its SI unit is in pascal-second (Pa.s) or N.m^-2.s. ![]() Chemists and physicists, on the other hand, normally use ‘n’ as a symbol. Fluid dynamicists, chemical engineers and mechanical engineers commonly consider the use of the Greek letter mu (µ) as the symbol to denote dynamic viscosity. In reality, they are two significantly different expressions.ĭynamic viscosity, which is also referred to as absolute viscosity, or just viscosity, is the quantitative expression of a fluid’s resistance to flow (shear). Many are confused between these two types of viscosity expression, and some even consider them to be one and the same. It can either be expressed as dynamic viscosity, or kinematic viscosity. There are two ways to report or measure a fluid’s viscosity. Viscosity can also be considered as a measure of the friction of fluids, as it also describes the internal resistance of the flow of fluid. On the other hand, honey is significantly ‘thick’, and is a fluid with a higher viscosity. Water is considered as ‘thin’, thus, the viscosity is lower. A great example of this, is the difference in the viscosities of water and honey. In common terms, viscosity is the thinness or thickness of the fluid. Viscosity expresses the fluid’s resistance against either tensional stress, or shear stress. The measure of that resistance is called viscosity. Sponsor this page to leave your contact info on this page.Every type of fluid possesses differing amounts of resistances against deformation. If you are a consultant, you may get yourself listed in CSP business directory (free) or You may also find an expert in CSP business directory below. If you have questions or need any help, please contact our sponsor. Under GHS, a hydrocarbon shall be classified as aspiration toxicity hazard category 1 if its kinematic viscosity is less than 20.5mm2/s (20 cSts) at 40 ☌. Usually, increased temperature reduces the viscosity of a liquid and makes it more hazardous. Liquids with lower viscosity are generally more hazardous because they can spread more quickly. Water at 20 ☌ has a kinematic viscosity of about 1 cSt. Fluent follows which viscosity dynamic or kinematic Old June 26, 2016, 11:18. Other units used include St and cSt.ġ cSt (centiStoke) = 1 mm2/s = 10^(?6)m2/s The SI unit of the kinematic viscosity is m2/s. The kinematic viscosity is the ratio between the dynamic viscosity and the density of a fluid. Kinematic Viscosity is a measure of the resistive flow of a fluid under the influence of gravity. You can often find it in the section 9 of a safety data sheet (SDS).ĭynamic Viscosity is a measure of a liquid’s resistance to its shearing flows, where adjacent layers move parallel to each other with different speeds. There are two types of viscosity: Dynamic viscosity and Kinematic viscosity. Viscosity is the measure of a liquid’s resistance to flow.
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