Dynamic viscosity is the coefficient of viscosity as defined in Newton’s law of viscosity. Non-Newtonian fluids do not follow Newton’s law of viscosity and hence their viscosity varies and is dependent on the shear rate. Newtonian fluids obey Newton’s law of viscosity. In another way, it can be stated that the ratio of shear stress to shear rate in a fluid is a constant, and is defined as the coefficient of viscosity. For a given temperature and pressure, Newton’s viscosity law states that the shear stress between two adjacent layers in a fluid is proportional to the velocity gradients between those layers. The relationship between the shear stress and the shear rate of fluid under mechanical stress is established by Newton’s law of viscosity. The following table states the viscosity of some popular substances. Temperature (☌) Kinematic Viscosity (m 2/s X 10 -6) 10 1.3059 20 1.004 30 0.801 50 0.553 70 0.413 90 0.326 100 0.294 Table 2: Kinematic Viscosity of water with respect to temperature Viscosity of Some Common Substances Table 2 below provides the kinematic viscosity of water. The kinematic viscosity of water can easily be obtained by dividing the above dynamic viscosity values by the water density. The following table provides the dynamic viscosity of water with respect to various temperatures. As for liquids, the viscosity decreases with an increase in temperature, the same is true for water. The viscosity of water at 20 0 C is 1 centipoise or 1 cP. Suspended Particles: Suspended materials increases viscosity.Multiphase flow: The viscosity of multiphase flow is affected by the volume of each phase.Liquids being incompressible does not have much impact. Pressure: With an increase in pressure, the viscosity of gases usually increases.Flow Conditions: For laminar flow, the viscosity of liquid remains constant while for turbulent flow viscosity changes.On the contrary, the viscosity of gases increases with an increase in temperature.
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