Viscosity is temperature dependent, generally the warmer a liquid the less viscous it is whereas the warmer a gas the higher the viscosity. To convert Kinematic viscosity in SSU to centiStokesĬentiStokes = 0.226 x SSU - (195/SSU) for SSU values less than 100, andĬentiStokes = 0.22 x SSU - (135/SSU) for SSU values greater than 100 Kinematic vicosity (SSU) = 4.63 x dynamic viscosity (cP) / SG This practice establishes the official equations relating SUS and SFS to the SI kinematic viscosity units, mm 2/s. The kinematic viscosity of a fluid can be calculated from its dynamic viscosity by dividing it by the fluid's density e.g.ĬentiPoises (cP) = centiStokes (cSt) / DensityĪ rough conversion of Redwood Seconds to centistokes is given by the formula:Ĭentistokes (cSt) = 0.260t - (0.0188/t), where t is the time in Redwood SecondsĪSTM D2161 - 05e1 Standard Practice for Conversion of Kinematic Viscosity to Saybolt Universal Viscosity or to Saybolt Furol Viscosity. Imperial units are square foot per second. In practice the centiStoke is used since the Stoke is a large unit. The metric units of kinematic viscosity are square centimetre per second, called a Stoke (called after Irish scientist George Gabriel Stokes). Most pipe friction charts and pump correction charts used by engineers refer to kinematic viscosity. Again, the larger the molecules, the greater resistance, the higher the kinematic viscosity. Kinematic viscosity on the other hand is a measure of a fluid's resistance to flow and shear under the forces of gravity. Imperial units are either slugs per foot-second, or the equivalent pound-seconds per square foot. In practice the centiPoise is used since the Poise is a large unit. The metric unit for dynamic viscosity is dyne-second per square centimetre (or sometimes the numerically equivalent gram per centimetre-second is used) called a Poise (named after French physician and physiologist Jean Louis Marie Poiseuille). The larger the molecules, the higher the internal resistance and consequently the higher the dynamic viscosity. This internal friction is caused by the resistance of the fluid's molecules moving relative to each other. It is more commonly measured in centistokes (cSt).The dynamic viscosity (sometimes called absolute viscosity) of a fluid can be defined as the resistance to flow and shear under the forces of internal friction. Kinematic viscosity has SI units of m 2 s -1. It is more commonly measured in centipose (cP). Units of Measurementĭynamic viscosity has SI units of Pa s. Kinematic viscosity measures this in terms of density, whereas dynamic viscosity does not. Difference Between Dynamic and Kinematic Viscosity Involvement of Densityīoth dynamic and kinematic viscosities measure how difficult it is for a fluid to flow. When the viscosity of a substance is quoted, the temperature should be specified. Note that since viscosity depends on temperature (the viscosity decreases as temperature increases in liquids, while the viscosity decreases when the temperature of a gas increases). However, the more commonly-used unit for measuring kinematic viscosity is the centistoke (cSt). The SI unit of kinematic viscosity is m 2 s -1. Kinematic viscosity ( ) of a fluid is the ratio of the fluid’s dynamic viscosity to its density : Non-Newtonian fluids cannot be described with one value for viscosity. Note that the above equation is only valid for so-called Newtonian fluids. In this sense viscosity is a measurement of how difficult it is to make a fluid flow. is a constant of proportionality, and it is known as the dynamic viscosity of the fluid. Where is the area of the layer and is the distance between the layers. The force required to move a layer of fluid in this way is related to the velocity at which the fluid layer will move by the equation: A force needs to be applied to a layer of fluid in order to make it flow at a constant speed relative to any other layer. Whenever a fluid flows against a surface, the different layers of fluid exert frictional forces between each other, causing them to flow at different speeds. The main difference between dynamic and kinematic viscosity is that dynamic viscosity is a measurement of how difficult it is for a fluid to flow whereas kinematic viscosity is the dynamic viscosity of a fluid divided by its density. Usually, two types of viscosity are quoted: dynamic and kinematic viscosity. Viscosity is very important to any process that depends on a flow of fluid. Main Difference – Dynamic vs. Kinematic Viscosity
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