3. Viscosity
• The device used for measurement of viscosity is known
as viscometer .
• The viscosity of a fluid is a measure of its resistance to gradual
deformation by shear stress or tensile stress.
• The units of viscosity is poise and centipoise .
• specific viscosity is the ratio of the viscosity of fluid to the
viscosity of water at 20 degree Celsius. Since the water has a
viscosity of 1 cp at 20 degree Celsius.
• Kinematic viscosity is defined as ratio of dynamic viscosity to
the density of the fluid.
4. Introduction
Definition
• A device used to measure the viscosity of a fluid. The saybolt
viscometer controls the heat of the fluid and the viscosity is the
time is takes the fluid to fill a container.
• Efflux cup viscometers are most commonly used for fieldwork
to measure the viscosity of oils, syrups, varnish, paints and
Bitumen emulsions.
• The saybolt viscometer, one of the efflux cup viscometers is
the standard instrument for testing petroleum products.
• The testing procedure is quite similar to the capillary-tube
viscometers
5. • Efflux time of a specified volume of fluid is measured through
fixed orifice at the bottom of a cup to represent the viscosity of
the fluid
• To obtain high accuracy the liquid holding vessel and orifice
are temperature controlled by immersing them in a
thermostatically controlled bath.
• There are three types of orifices available-Universal, Furol,
Asphalt.
• The furol and asphalt orifices, respectively, have an efflux time
of approximately, one-tenth and one-hundredth that of the
universal orifice.
6.
7. • The cup orifice combination should be selected to provide an
effllux time within the range of 20 to 100 seconds.
• Of these types, the universal orifice(saybolt universal
viscometer) is most commonly used and its efflux time is
designated as saybolt universal seconds(SUS).
• The universal viscometer measures the time required for 60 cc
of sample fluid to flow out through an orifice having
dimensions of 0.176 cm in diameter and 1.225 cm in length.
8. • Saybolt universal seconds (t) can be converted to kinematic
viscosity (v) by the following equations:
When t < 100 secs, v = 0.226t - 195/t Centistokes
When t >100 secs, v = 0.220t - 135/t Centistokes.
• The viscosity determinations should be conducted in a room
free from drafts and rapid changes in temperature the highest
degree of accuracy.
9. ADVANTAGES
• It has a digital meter to measure tempertature and so reading is
more accurate and precise.
• The coils wrap around the container uniformly so uniform
temprature can be obtained.
• Viscosity can be directly compared for two or more liquids.
10. Disadvantages
• The main disadvantage of the capillary tube viscometer is the
errors that arise due to the variation in the head loss and other
parameters.
• Efflux cup viscometer have some inherent inaccuracies
11. Application
• Efflux viscometer are most commonly used fieldwork
to measure the viscosity of oil , syrups, varnish,
paints.
• It is used for testing petroleum products.
