A viscometer is an instrument which is used to measure the viscosity of a fluid. Viscosity is nothing but the liquid’s resistance to the flow. They work by comparing the fluid flow to a stationary object. Viscometers are used when the viscosity of a fluid does not change with flow conditions. In case the viscosity changes with flow conditions, a rheometer can be used for measurement.
There are different kinds of viscometers available like,
- U-tube viscometers, also called glass capillary viscometers or Ostwald viscometers. There are used to measure viscosity of a sample, when the density of the fluid is known. The time taken for a known volume of the liquid to flow through the capillary, under the influence of gravity, is recorded. Before using this instrument to measure the viscosity of an unknown sample, it must be calibrated using a sample of known viscosity. In case of opaque samples, visualization is tough and hence it is difficult to determine when the sample passed the marked points. Hence reverse-flow type viscometers are used which wet only the timing section during measurement.
- Falling sphere viscometer: This type of viscometer measures the time a ball/ sphere takes to fall through a sample filled tube, due to gravity.
- Rotational viscometer: Also known as a Brookfield viscometer, make use of a torsion spring to measure the torque required to rotate the spindle in the sample.
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