Wednesday, 10 October 2012

Viscosity of oils

Information

This method uses an instrument known as a cup viscometer to measure the viscosity of a fluid.  A cup viscometer is essentially just a smooth sided cup with a hole in the bottom. A preliminary experiment may be required if you are making a cup viscometer to determine the correct volume of oil and hole size to use. You need to be able to use the same cup for all your oil samples and it should be set up such that the oil does not drain so quickly it is difficult to time, nor that it takes so long as to be impractical to complete multiple tests in a reasonable period of time.

Equipment

Clamp and stand
Cup viscometer
Bung for hole in viscometer
Collecting beaker
Measuring cylinder
Stopclock
Samples of different oils

Method

Set up the viscometer in the clamp and stand so that the beaker can be placed below it and you can see the oil flow.
Place a known volume of oil into the viscometer with the bung in the hole.
Place the collecting beaker under the hole.
Start a stopclock as you remove the bung and wait for the oil to drain.
When the oil has finished draining stop the clock and record the time.
Repeat twice more for this oil sample and repeat the whole process for each oil sample to be tested.

Sometimes very viscous oils will start to drip during the final parts of draining. If this is the case it is suggested that you time until each oil first starts to drip.

Try to ensure that the room temperature and thus oil temperature remains constant as the temperature of the oil affects the flow rate.