Anything over 25cP will have a significant effect on the performance of a centrifugal pumps. Viscosity will have significant effects on flow rates and pressure capabilities of centrifugal pumps as well shaft torque and available power, the efficiency will obviously be lower. When shear is applied to non-Newtonian fluids, the viscosity of the fluid changes (e.g. Non-Newtonian fluids are the opposite of Newtonian fluids. In simple terms, a Newtonian fluid’s viscosity remains constant, no matter the amount of shear applied for a constant temperature (e.g. Kinematic viscosity is used to measure Newtonian liquids, dynamic viscosity for non-Newtonian liquids. Therefore, we say that steel has a greater density than ice. They may be the same size, but the steel cube weighs more than the ice cube. Think about an 1cm3 ice cube and a 1cm3 cube of steel. The formula for the conversion is:ĭensity is the ratio of the mass (or weight) of the sample divided by the volume of the sample. Density actually provides a way to convert between a kinematic and a dynamic viscosity measurement. What’s the difference between dynamic and kinematic viscosity?Ī basic difference between the dynamic and kinematic viscosity measurements is density. The unit of measure of kinematic viscosity is Centistokes (cSt). So kinematic viscosity is the measure of a fluid’s inherent resistance to flow when no external force, except gravity, is acting on it. The other way is to measure the resistive flow of a fluid under the weight of gravity. This is dynamic viscosity and the unit of measure for dynamic viscosity is Centipoise (cP) One way is to measure a fluid’s resistance to flow when an external force is applied. To achieve a viscosity of 800 cSt as shown in the example, 68% of 1000 cSt and 32% of 500 cSt fluids are blended.When people talk about understanding viscosity, they are talking about one of two things: dynamic (also known as absolute) viscosity or kinematic viscosity. When fluids covering a wider range are blended, the chart will only approximate the finished viscosity. This method is reasonably accurate in predicting blend viscosity when the two fluids differ in viscosity by no more than one magnitude (one power of ten). From this point, follow down to the horizontal scale to read the percent of the higher viscosity fluid to use in the blend.Locate the point where the line indicating the desired blend viscosity intersects the constructed line.Connect these two points with a straight line.Locate the higher viscosity on the right hand scale. Locate the lower viscosity on the left hand scale.For high accuracy, measure the actual viscosity of the blending fluids. Decide upon the viscosity grades to be blended.This chart provides a means for determining the proper blend ratio. To correct for density in converting from centistokes to centipoises, multiply specific gravity by centistokes.Īny standard viscosity grade of polydimethylsiloxane can be blended together with another viscosity grade of the same fluid to produce an intermediate viscosity. It assumes that the density of liquids is 1 so that stokes and poises are the same and that viscosity is independent of shear rate, i.e., the fluid is Newtonian. Note: The precision of conversion in this table is limited by two factors. Viscosities at 25 ☌ unless otherwise stated
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