![]() For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Includes over 250 free problems with complete detailed solutions.The viscosity of a fluid is a measure of its resistance to deformation at a given rate. Practice Homework and Test problems now available in the 'Eng Fluids' mobile app The CGS system is cm 2/s and this is referred as a stoke (St). The SI unit for the kinematic viscosity is m 2/s. The kinematic viscosity is the ratio of absolute viscosity and density. For example, crude oil is often heated to a higher temperature to reduce the viscosity for transport. ![]() For liquids, the viscosity decreases with temperature, whereas for gases, the viscosity increases with temperature. However, viscosity depends greatly on temperature. Viscosity is not a strong function of pressure, hence the effects of pressure on viscosity can be neglected. Note that only Newtonianįluids will be considered in the future discussion non-NewtonianĮffects are beyond the scope of this eBook. Like a fluid once this yield stress is exceeded. Withstand a finite shear stress without any motion, however it moves The larger theĪpplied shear rate trying to mix water with corn starch, more resistanceĪnother non-Newtonian fluid is Bingham plastic, The less resistance that (viscosity) is encountered.įluids are quicksand and a water-corn starch mixture. Whenīrushing paint on a wall, note that the larger the applied shear rate, An example of a shear thinning fluid is latex paint. Rate, whereas for shear thickening fluids, the apparent viscosity increases The apparent viscosity is the same as the viscosity and is not a functionįor shear thinning fluids, the apparent viscosity decreases with shear The shear stress versus the rate of shear strain. Viscosity is introduced and it represents the slope (not constant) of Non-Newtonian fluids are shear thinning fluids, shear thickeningįluids and Bingham plastic. Note that the shear stress can also be determined by dividing the shearįor non-Newtonian fluids, the shear stress is not a linearįunction of the rate of shear strain. Is also expressed in the CGS system as dyne-s/cm 2 and The absolute viscosity, dynamic viscosity or simply the viscosity. The proportionality constant (μ) is called The above equation is referred to as Newton's law of viscosity. Rate of shear strain in a linear fashion. ![]() Most common fluids, such as water, air and oil, areĬalled Newtonian fluids in which the shear stress is related to the Strain) in this case is a constant (du/dy = U/h). Note that the velocity gradient (also known as the rate of shear Of the fluid motion between the plates is assumed to be linear and is The fluid is stuck to the bottom plate, u = 0). ![]() Plate moves with the plate velocity U and no-slip condition is applied If the top plate is movedĪt a velocity U while the bottom plate is fixed, the fluid Two parallel plates, as shown in the figure. To illustrate the concept of viscosity, consider a fluid between Viscosity is a fluid property that measures the resistance eCourses.ou.edu will close.Īnother important fluid property will be introduced in New eBook website Please update bookmarks. ![]()
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