The speed of turning the probe can be adjusted in the rotational viscometer as it moves in the liquid. The dynamic viscosity is determined by measuring the torque or force A probe is present in the rotational viscometer, which is rotated in the liquid sample. The peculiarity of non-Newtonian fluids is that there is a change in the viscosity depending on the conditions to which they are exposed. Rotational viscometers are commonly used to measure the viscosity of non-Newtonian liquids. The most commonly used instrument to measure dynamic viscosity is a rotational viscometer. Measurement Methods for Dynamic and Kinematic Viscosity Dynamic Viscosity Measurements Whenever the fluid used is not subjected to physical forces other than gravitational force, kinematic viscosity is the best measurement. The changes in viscosity under different temperatures or environmental conditions are evaluated and are useful for the effectiveness of fluids such as gasoline, lubricating oil, and glycerine. In Newtonian fluids, the viscosity does not change with applied force or shear rate. When external forces are applied to the fluid, dynamic viscosity measurements are the best choice. As the speed of fluid movement varies with pump velocity and pressure, dynamic viscosity measurements are necessary for such fluid systems. The other important application requiring dynamic viscosity measurements is the design of pumping systems. In such a fluid application, dynamic viscosity should be measured. For such fluids, determining the internal resistance is important to calculate the force required to move the fluid. When a fluid changes its characteristics upon the application of force or pressure, it is a non-Newtonian fluid. The table below compares the dynamic viscosity and kinematic viscosity of liquid water from 0℃ to its normal boiling point.Ĭhoosing the Proper Measurement Dynamic Viscosity The viscosity of liquid water decreases with an increase in temperature. There are several engineering properties for water, including thermal expansion, isothermal compression, thermal conductivity, specific heat, specific entropy, specific enthalpy, saturation vapor pressure, dynamic viscosity, and kinematic viscosity. The Dynamic and Kinematic Viscosity of Water The table above compares the properties of dynamic viscosity vs. However, there is no way that the kinematic viscosity of two different fluids can be the same due to the differences in their density. The dynamic viscosity of two different fluids can be the same. The kinematic viscosity gives the inherent resistance of the fluid to flow when there is no external force applied to it except gravity. When the resistance to flow is measured under the weight of gravity, then the viscosity is called kinematic viscosity. The dynamic viscosity measures the resistance offered by the fluid to the flow when an external force is applied. The dynamic viscosity divided by the density of the fluid gives kinematic viscosity. The absolute or dynamic viscosity is the ratio of shear stress to shear strain. In this article, we will compare the dynamic vs. kinematic viscosity, it is important to note that no two fluids can have the same kinematic viscosity, but they can have the same dynamic viscosity. The viscosity of fluids can be expressed in terms of either dynamic viscosity or kinematic viscosity. Fluids differ in the internal resistance that is exerted, causing differences in viscosity as well. In fluids, the resistance to flow or to deform is known as viscosity. In fluids, the resistance to flow or to deform is known as viscosity Whenever a fluid is not subjected to physical forces other than gravitational force, kinematic viscosity is the right measurement. When external forces are applied to a fluid, dynamic viscosity measurements are the best choice. No two fluids can have the same kinematic viscosity, but they can have the same dynamic viscosity.
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