Importance Of Viscosity Of Lubricating Oil

EXPERIMENT NO. 8

AIM: Determination of Viscosity of Lubricating oil at different temperatures by Redwood Viscometer No.1 or 2

THEORY:

Viscosity is one of the most important properties of lubricating oil. The formation of a constant fluid film of a lubricating between the moving surface under particular condition of load, speed and lubricant supply is depend upon the viscosity of lubricating oil. If the viscosity of the oil is too low the fluid lubricant film cannot be maintained between the moving surfaces as results of which excessive wear may takes place. On the other hand if the viscosity of lubricating oil is too high excessive friction due to the shearing of oil itself would result. Hence it is essential to have knowledge of the viscosity of lubricating oil.

Viscosity is a measure of the internal resistance to motion of a fluid and is mainly due to the forces of cohesion between the fluids molecules.

Absolute viscosity may be defined as the tangential force per unit area required to maintained unit velocity gradient between two parallel planes in the fluid at unit distance apart. It is denoted by eta (η). Its unit in CGS system is poise and centipoises.

The ratio of absolute viscosity to density for any fluid is known as its absolute kinematics viscosity. It denoted by (u). And its units are stokes & centistokes.

Kinematics

Engle Viscometer in Europe & Say bolt viscometer in the USA. In these viscometers, a fixed volume of the liquid is allowed to flow through a capillary tube of specified dimension under given set of condition the time of flow is measured at particular temperature. The viscosity of the oil so determined in the time unit is sometimes called as relative viscosity. The kinematics viscosity of the oil is calculated centistokes from the time taken by the oil to flow through the standard orifice of the instrument with help of the following