This document discusses viscosity and provides instructions for measuring the viscosity of liquids using a Cannon-Fenske capillary viscometer. It defines viscosity as a fluid's resistance to flow and explains that viscosity decreases with increasing temperature for liquids and increases with temperature for gases. The procedure involves cleaning and filling the viscometer, submerging it in a temperature-controlled bath, measuring the efflux time for fluid to pass between marks, and using that time and the viscometer constant to calculate kinematic and dynamic viscosity.

1. DUHOK POLYTECHNIC UNIVERSITY
ZAKHO TECHNICAL INSTITUTE
PETROLEUM DEPARTMENT
OIL AND GAS TECHNOLOGY 2/ PRACTICAL
Practical Test No. 6
VISCOSITY

2. What is Viscosity
Most fluids offer some resistance to motion, and we call this resistance “viscosity.” Viscosity
arises when there is relative motion between layers of the fluid. More precisely, it measures
resistance to flow arising due to the internal friction between the fluid layers as they slip past one
another when fluid flows. Viscosity can also be thought of as a measure of a fluid’s thickness or
its resistance to objects passing through it.
A fluid with large viscosity resists motion because its strong intermolecular forces give it a lot of
internal friction, resisting the movement of layers past one another. On the contrary, a fluid with
low viscosity flows easily because its molecular makeup results in very little friction when it is
in motion. Gases also exhibit viscosity, but it is harder to notice in ordinary circumstances.
Viscosity Definition
The definition of viscosity is as follows:
Viscosity is a measure of a fluid’s resistance to flow.
The SI unit of viscosity is poiseiulle (PI). Its other units are newton-second per square metre
(
𝑁 𝑠
𝑚2) or pascal-second (Pa s.) The dimensional formula of viscosity is (
𝑀
𝐿 𝑇
)
The viscosity of liquids decreases rapidly with an increase in temperature, and the viscosity of
gases increases with an increase in temperature. Thus, upon heating, liquids flow more easily,
whereas gases flow more slowly. Also, viscosity does not change as the amount of matter
changes, therefore it is an intensive property.

3. Scope
This test method specifies a procedure for the determination of the kinematic viscosity of liquid
petroleum products. The dynamic viscosity can be obtained by multiplying the kinematic
viscosity, by the density of the liquid.
Significance and Use
Many petroleum products, and some non-petroleum materials, are used as lubricants, and the
correct operation of the equipment depends upon the appropriate viscosity of the liquid being
used. In addition, the viscosity of many petroleum fuels is important for the estimation of
optimum storage, handling, and operational conditions. Thus, the accurate determination of
viscosity is essential to many product specifications.
Apparatus
Following apparatus required for a Viscosity test:
1. Cannon-Fenske capillary Use glass capillary type viscometers, capable of being used to
determine kinematic viscosity within the limits of the precision given in the precision section.
2. Water bath —Use a liquid bath of sufficient depth such, that at no time during the
measurement of flow time, any portion of the sample in the viscometer is less than 20 mm below
the surface of the bath liquid or less than 20 mm above the bottom of the bath.
3. Thermometer or Temperature indicator– in the range from 0 to100°C
4. Time device: a suitable time device like a stopwatch, electric timer, or another spring-actuated
device.
5. Sample sufficient amount of sample.
6. Rubber-Tube and sucking rubber ball to suck liquid.

4. Typical representatives of glass capillaries
Established types of glass capillaries:
1. Ostwald capillary (named after Wilhelm Ostwald, 1853 – 1932, German chemist)
2. Ubbelohde capillary (named after Leo Ubbelohde, 1877 – 1964, German chemist)
3. Cannon-Fenske capillary (a modified Ostwald capillary, designed by Dr. Michael R.
Cannon, American scientist, inventor, and educator, and Merrell Robert Fenske, 1904 –
197
4. Houillon capillary (Standard ASTM D7279 describes measurement using this capillary
type)

5. Procedure
1. The viscometer should be cleaned with a suitable
solvent and dried in a stream of clean.
2. If a possibility of lint, dust, or other solid material
is present in the liquid sample, this may be removed by
filtering through sintered glass filter or fine mesh
screen. (NB: This may not be feasible with crude oils.)
3. To introduce sample into the viscometer, invert
viscometer, immerse tube “A” into liquid and apply
suction to “I”, which causes the sample to rise to
etched line “E”. Turn the viscometer to normal position
and wipe tube “A” clean.
4. Insert the viscometer into a holder and place in
constant temperature bath. Allow 10 minutes for
viscometer to reach equilibrium at 100°F (38°C) or 15
min at 210°F (98.89°C), or whatever amount of time is
required for temperature equilibration.
5. Vertical alignment may be accomplished in bath by
suspending a plumb bob in tube “I”.
6. Apply suction to tube “A” and bring sample into bulb “B” a short distance above mark
“C”.
7. The efflux time is measured by allowing the sample to flow freely through mark “C”,
measuring the time for the meniscus to pass from “C” to “E”.
8. To repeat efflux time measurement, repeat steps 7 and 8.
9. The kinematic viscosity is calculated by multiplying the efflux time by the viscometer
constant.
kinematic viscosity (cSt) = Time × viscometer constant
dynamic viscosity (cP) = kinematic viscosity (cSt) × density (g/cm3
)

6. Discussion
1- How does viscosity of liquids vary with pressure?
2- How does viscosity vary with temperature?
3- What factors affect viscosity?
4- What are the types of viscosity?
5- What is the use of Cannon-Fenske capillary viscometer?