The viscosity of the oil can either increase or decrease. If this happens the oil should be changed. If the viscosity of the oil deviates greatly from the initial values of the fresh oil, this is an indication that accelerated oil aging has occurred. A fluid may be made up of molecules that vary in size, shape, and cohesiveness or a single type of molecule. Absolute Viscosity: Diffusivity of momentum: Represents: The viscous force of the fluid: Inertia as well as viscous force. This viscosity is the ratio of dynamic viscosity to density. Not only does oil change its viscosity due to temperature influences and pressure, but the environmental influences during operation can also have a lasting effect on the flow properties. the quality or state of being viscous ( thick and sticky and not flowing easily): The viscosity of the fluid in the system can be modified. Viscosity is a measure of a fluidвЂ™s internal friction (resistance to flow) when one layer of fluid is forced to move in over another layer. Dynamic Viscosity: Kinematic Viscosity: Definition: Dynamic viscosity is the measurement of the fluidвЂ™s internal resistance to flow. In addition, the viscosity index of oils can be artificially increased by adding high-performance additives (VI improvers). In the meantime, the scale has reached values of up to 400, due in part to modern production processes for temperature-stable synthetic oils. The viscosity index started at 0 (very temperature-dependent oils) and went up to 100 (oils with low temperature dependence). When the viscosity index was developed in 1928, the scale was based on the mineral oil types known at the time. Their lubricating properties become unstable at high or low temperatures. The oils with a low viscosity index can be influenced more strongly by the temperature. The oil retains its lubricating properties in a wider temperature range. Oil with a high viscosity index is less temperature dependent. To a certain extent, the viscosity index is also an indication of the quality of an oil and serves the comparability of different oil types. The viscosity behaviour at 40 вЊ and 100 вЊ is measured. It refers to the kinematic viscosity of an oil. If we define the magnitude of the strain rate tensor,, so that it will be the argument for the viscosity function, one of the invariants is zero for shear flows and another is zero for incompressible flow 1, leaving the second invariant as the choice for an argument of the function, ( ). The viscosity index (VI) is the behaviour of the lubricant as a function of temperature.

Viscosity definition