The resistance to movement is defined as viscosity. Viscosity is the most important quality of lubricating oils in lubrication, and it is also highly important in greases, which is frequently overlooked. Highly viscous oils (for example, grease) are employed in heavy machinery. Thin oils with low viscosity (for example, lubricating oil used in clocks) are utilized in light machinery. Knowing the coefficient of viscosity and how it varies with temperature allows us to select the best lubricant for each machine.The coefficient of viscosity of organic liquids is used to calculate their molecular weights.Some applications of its knowledge are discussed as under: Knowledge of the viscosity of various liquids and gases has been put to use in daily life. By multiplying the time measured by the factor of the viscometer, the kinematic viscosity is obtained. The time taken by the test liquid to flow between two points is measured. Most commercial units are provided with a conversion factor. The time taken for the liquid to pass between these marks is proportional to the kinematic viscosity. Two marks (one above and one below the upper bulb) indicate a known volume. In use, the upper bulb draws the liquid by suction, and then the liquid is made to flow down through the capillary into the lower bulb. Above, is a bulb, and with it is another bulb lower down on the other arm, as shown in the image. In one arm of the U is the capillary, a vertical section of a precise narrow bore. U-tube viscometers are generally called Glass Capillary Viscometers or Ostwald Viscometers.Ī viscometer consists of two reservoir bulbs and a capillary tube. This method doesn’t provide an accurate idea of the viscosity for accurate measurement U-Tube Viscometer is used. The slower the metal ball falls, the greater the viscosity of the liquid. Viscosity of any liquid is measured by dropping a metal ball through the liquid and measuring the time of the fall of the metal ball. on applying shear, the viscosity of non-Newtonian fluids changes, depending on the fluid.Įxamples: Ketchup, Quicksand, Silly Putty, etc. Non-Newtonian fluids are the opposite of Newtonian fluids i.e. There is a linear relationship between viscosity and shear stress in the case of Newtonian Fluid.Įxamples: Water, Alcohol, Petroleum, and others. Newtonian FluidsĪny fluid whose viscosity remains constant when the amount of shear is applied at a constant temperature is called Newtonian fluid. So on this basis we have two types of liquid that are, The viscosity of any liquid is directly influenced by the change in pressure and temperature in the liquid. The table given below lists some fluids and their coefficient of viscosity at different temperatures:
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