Viscometer

A viscometer (also called viscosimeter) is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a rheometer can be considered as a special type of viscometer.^[1] Viscometers can measure only constant viscosity, that is, viscosity that does not change with flow conditions.

In general, either the fluid remains stationary and an object moves through it, or the object is stationary and the fluid moves past it. The drag caused by relative motion of the fluid and a surface is a measure of the viscosity. The flow conditions must have a sufficiently small value of Reynolds number for there to be laminar flow.

At 20 °C, the dynamic viscosity (kinematic viscosity × density) of water is 1.0038 mPa·s and its kinematic viscosity (product of flow time × factor) is 1.0022 mm²/s. These values are used for calibrating certain types of viscometers.

^ Barnes, H. A.; Hutton, J. F.; Walters, K. (1989). An introduction to rheology (5. impr. ed.). Amsterdam: Elsevier. p. 12. ISBN 978-0-444-87140-4.

[1] Barnes, H. A.; Hutton, J. F.; Walters, K. (1989). An introduction to rheology (5. impr. ed.). Amsterdam: Elsevier. p. 12. ISBN 978-0-444-87140-4.

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