To determine the kinematic viscosity and absolute viscosity of the given thick sample of oil (highly viscous) at various temperatures and to study the variations of viscosity with temperature by using Redwood viscometer No. 2.
Viscosity is the property of a liquid by virtue of which it offers resistance to its own flow. The viscosity of liquids decreases with increasing temperature. The rate at which the viscosity changes with temperature is known as viscosity index.
Redwood viscometer No. 2, two thermometers (0–100°C), a narrow-necked flask (50 cc), a stop watch.
It is a silver plated brass cylinder. The upper end of the cup is open. The bottom of the cylinder is fitted with an agate jet (with a diameter of 3.8 mm and a length of 15 mm). The jet is opened or closed by a valve rod, which is a small silver-plated brass ball fixed to a stout wire. The level to which the cylinder is to be filled with oil is indicated by a pointing wire fixed on the inner side of the cylinder. The lid of the cup is fitted with a thermometer, which indicates the temperature of the oil.
The oil cup is surrounded by a cylindrical copper bath containing water. It is provided with a tap for water outlet and an electric heating coil is fixed at the bottom. A thermometer fixed in the water jacket indicates the temperature of the water.
Outside the cylinder, there is a stirrer, carrying blades, for stirring the water in the bath for maintaining a uniform desired temperature. The stirrer is provided with a cylinder shield at the top to prevent the water from splashing into the oil cylinder.
The entire apparatus rests on the three keys provided at the bottom with levelling screws.
It is a specially shaped flask for receiving oil from the jet outlet. Its capacity is 50 ml up to the mark in its neck.
Kinematic viscosity of oil = centistokes (centipoise).
Here, t = time taken for collecting 50 cc of oil, A and B are viscometer constants. A = 0.26 and B = 171.5.
Density of oil at different temperatures = T − T r
Here, T = Density of oil at tested temperature
T r = Density of oil at room temperature
It is observed from the graphs that as the temperature increases, the Redwood seconds, kinematic viscosity and absolute viscosity decrease.
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