Alexandria University
Faculty of engineering
Gas and petrochemical engineering program
GPE423:Petroleum refining engineering
Fall 2019
Viscometer
Name:
Mazen fathy
Moustafa emad
ID:
5079
5070
Contents
Introduction.....................................................................................................................................1
What is viscosity?.............................................................................................................................1
Importance of viscosity....................................................................................................................2
Main conscept of viscometer..........................................................................................................3
References.......................................................................................................................................5
Introduction
A viscometer (also called viscosimeter) is an instrument used to measure the
viscosity of Newtonian fluids. 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.
Viscometers only measure under one flow condition. 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.
What is viscosity?
Viscosity is a measure of a fluid's resistance to flow. It describes the internal
friction of a moving fluid. A fluid with large viscosity resists motion because its
molecular makeup gives it a lot of internal friction.
A fluid with low viscosity flows easily because its molecular makeup results in
very little friction when it is in motion. Gases also have viscosity, although it is a
little harder to notice it in ordinary circumstances
1
Importance of viscosity
Viscosity is the ability of a liquid to resist its flow, when subjected to some
force or shear or pressure or tension.
A liquid is said to be less viscous if it flows easily, eg. water. On the other
hand curd is comparatively more viscous than water and therefore it does
not show ease in its movement or flow.
here we can understand that importance of Viscosity is movement of flow.
2
The viscosity of an object depends on its temperature. Usually the viscosity
decreases as the temperature increases. If the temperature increases the
viscosity decreases.
Substances that flows fast means that they have a low viscosity.
Its important to quality control applications in the production of a wide variety of
products, including inks, paints, motor oils, foods, pharmaceuticals and cosmetics,
to name just a few.
Main conscept of viscometer
I. U-tube viscometers
These devices are also known as glass capillary viscometers or Ostwald
viscometers, named after Wilhelm Ostwald. Another version is the
Ubbelohde viscometer, which consists of a U-shaped glass tube held
vertically in a controlled temperature bath.
In one arm of the U is a vertical section of precise narrow bore (the
capillary). Above there is a bulb, with it is another bulb lower down on the
other arm. In use, liquid is drawn into the upper bulb by suction, then
allowed to flow down through the capillary into the lower bulb. Two marks
(one above and one below the upper bulb) indicate a known volume.
3
The time taken for the level of the liquid to pass between these marks is
proportional to the kinematic viscosity. The calibration can be done using a
fluid of known properties. Most commercial units are provided with a
conversion factor. The time required for the test liquid to flow through a
capillary of a known diameter of a certain factor between two marked points
is measured. By multiplying the time taken by the factor of the viscometer,
the kinematic viscosity is obtained.
II. Falling-sphere viscometers
Stokes' law is the basis of the falling-sphere viscometer, in which the fluid is
stationary in a vertical glass tube. A sphere of known size and density is
allowed to descend through the liquid. If correctly selected, it reaches
terminal velocity, which can be measured by the time it takes to pass two
marks on the tube.
Electronic sensing can be used for opaque fluids. Knowing the terminal
velocity, the size and density of the sphere, and the density of the liquid,
Stokes' law can be used to calculate the viscosity of the fluid. A series of
steel ball bearings of different diameter are normally used in the classic
experiment to improve the accuracy of the calculation.
4
The school experiment uses glycerol as the fluid, and the technique is used
industrially to check the viscosity of fluids used in processes. It includes
many different oils and polymer liquids .
References
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.
2. ^ W. P. Mason, M. Hill: Measurement of the viscosity and shear elasticity of
liquids by means of a torsionally vibrating crystal; Transactions of the ASME. In:
Journal of Lubricating Technology. Band 69, 1947, S. 359–370.
3. ^ Berthold Bode: Entwicklung eines Quarzviskosimeters für Messungen bei
hohen Drücken. Dissertation der TU Clausthal, 1984.
