Viscometer checks viscosity in ranges of: Measurement with a viscometer - by testing the torque (resistance force) required to maintain a constant rotational speed. Kinematic measurement: By measuring the flow time in glass piping at a certain temperature. There are several methods for measuring viscosity: Viscosity measurements are very useful in the food, cosmetics, oils and fuels industry and more.It is important for manufacturers that the flow of material remains the same.Manufacturers test the viscosity of the raw materials and their products during production and of course of the final product. In which industries is viscosity measured? They measure the torque required to rotate a disk or bob in a fluid at a known speed. Rotational viscometers use the idea that the torque required to turn an object in a fluid is a function of the viscosity of that fluid. Water at 20☌ has a viscosity of 1.0020 cP. It is more commonly expressed, particularly in ASTM standards, as centipoise (cP). The cgs physical unit for dynamic viscosity is the poise. s, while a typical motor oil could have a viscosity of about 0.250 Pa.The SI physical unit of dynamic viscosity is the pascal-second (Pa The dynamic (shear) viscosity of a fluid expresses its resistance to shearing flows, where adjacent layers move parallel to each other with different speeds A liquid whose viscosity is less than that of water is sometimes known as a mobile liquid, while a substance with a viscosity substantially greater than water is called a viscous liquid. For liquids, it corresponds to the informal notion of 'thickness'. In the Couette flow, a fluid is trapped between two infinitely large plates, one fixed and one in parallel motion at constant speed u can be important is the calculation of energy loss in sound and shock waves, described by Stokes' law of sound attenuation, since these phenomena involve rapid expansions and compressions.The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. Although it applies to general flows, it is easy to visualize and define in a simple shearing flow, such as a planar Couette flow. Viscosity is the material property which relates the viscous stresses in a material to the rate of change of a deformation (the strain rate). For instance, in a fluid such as water the stresses which arise from shearing the fluid do not depend on the distance the fluid has been sheared rather, they depend on how quickly the shearing occurs. In other materials, stresses are present which can be attributed to the rate of change of the deformation over time. Stresses which can be attributed to the deformation of a material from some rest state are called elastic stresses. For instance, if the material were a simple spring, the answer would be given by Hooke's law, which says that the force experienced by a spring is proportional to the distance displaced from equilibrium. In materials science and engineering, one is often interested in understanding the forces or stresses involved in the deformation of a material. In a general parallel flow, the shear stress is proportional to the gradient of the velocity. A fluid that has zero viscosity is called ideal or inviscid. Zero viscosity (no resistance to shear stress) is observed only at very low temperatures in superfluids otherwise, the second law of thermodynamics requires all fluids to have positive viscosity. For example, the viscosity of a Newtonian fluid does not vary significantly with the rate of deformation. However, the dependence on some of these properties is negligible in certain cases. In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. 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. The viscosity of a fluid is a measure of its resistance to deformation at a given rate.

Viscosity of water in pa s