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```In the name of Allah, Most
Gracious, Most Compassionate
>> Viscosity
Group Members
Aqsan Naveed
Umer Zahid
Mohsin Mahmood
Aqsam Naveed
>>> Definition
Viscosity is an internal property of a fluid that
offers resistance to flow.
The resistance of a substance to flow. For
example, water has a lower viscosity than
molasses and flows more easily. Viscosity is
related to the concept of shear force
It can be understood as the effect of
different layers of the fluid exerting shearing
force on each other, or on other surfaces, as
they move against each other.
Types of “Viscosity ”
Dynamic (absolute) Viscosity
It is the tangential force per
unit area required to move one
horizontal plane with respect to
the other at unit velocity when
maintained a unit distance apart
by the fluid.
The shearing stress between
the layers of non turbulent fluid
moving in straight parallel lines
can be defined for a Newtonian
fluid
• The dynamic or absolute viscosity can be
expressed like
• τ = μ dc/dy
(1)
• where
• τ = shearing stress
• μ = dynamic viscosity
• Equation (1) is known as the Newtons
Law of Friction.
• In the SI system the dynamic viscosity units are N s/m2,
Pa s or kg/m s where
• 1 Pa s = 1 N s/m2 = 1 kg/m s
• The dynamic viscosity is also often expressed in the
metric CGS (centimeter-gram-second) system as
g/cm.s, dyne.s/cm2 or poise (p) where
• 1 poise = dyne s/cm2 = g/cm s = 1/10 Pa s
• For practical use the Poise is to large and it's usual
divided by 100 into the smaller unit called the centiPoise
(cP) where
• 1 p = 100 cP
• Water at 68.4oF (20.2oC) has an absolute viscosity of
one - 1 - centiPoise.
Kinematic Viscosity
• is the ratio of absolute or dynamic viscosity to density - a
quantity in which no force is involved. Kinematic viscosity
can be obtained by dividing the absolute viscosity of a
fluid with it's mass density
• ν=μ/ρ
(2)
• where
• ν = kinematic viscosity
• μ = absolute or dynamic viscosity
• ρ = density
• In the SI-system the theoretical unit is m2/s or commonly
used Stoke (St) where
• 1 St = 10-4 m2/s
• Since the Stoke is an unpractical large
unit, it is usual divided by 100 to give the
unit called Centistokes (cSt) where
• 1 St = 100 cSt
• 1 cSt = 10-6 m2/s
• Since the specific gravity of water at
68.4oF (20.2oC) is almost one (1), the
kinematic viscosity of water at 68.4oF is
for all practical purposes 1.0 cSt.
Viscosity and Reference
Temperatures
• The viscosity of a fluid is highly temperature
dependent and for either dynamic or kinematic
viscosity to be meaningful, the reference
temperature must be quoted. In ISO 8217 the
reference temperature for a residual fluid is
100oC. For a distillate fluid the reference
temperature is 40oC.
• For a liquid - the kinematic viscosity will
decrease with higher temperature
• For a gas - the kinematic viscosity will increase
with higher temperature
Comparison of
temperaturedependent
• viscosities
– Gas: oxygen
• Increase with temperature
• Liquid: aniline
– Decrease with temperature
Other Commonly used Viscosity
Units
• Saybolt Universal Seconds (or SUS, SSU)
• Saybolt Universal Seconds (or SUS) is used to measure
viscosity. The efflux time is Saybolt Universal Seconds
(SUS) required for 60 milliliters of a petroleum product to
flow through the calibrated orifice of a Saybolt Universal
viscometer, under carefully controlled temperature and
as prescribed by test method ASTM D 88. This method
has largely been replaced by the kinematic viscosity
method. Saybolt Universal Seconds is also called the
SSU number (Seconds Saybolt Universal) or SSF
number (Saybolt Seconds Furol).
• Kinematic viscosity versus dynamic or
absolute viscosity can be expressed as
• ν = 4.63 μ / SG
(3)
• where
• ν = kinematic vicosity (SSU)
• μ = dynamic or absolute viscosity (cP)
Degree Engler
• Degree Engler is used in Great Britain as a scale
to measure kinematic viscosity. Unlike the
Saybolt and Redwood scales, the Engler scale is
based on comparing a flow of the substance
being tested to the flow of another substance water. Viscosity in Engler degrees is the ratio of
the time of a flow of 200 cubic centimetres of the
fluid whose viscosity is being measured - to the
time of flow of 200 cubic centimeters of water at
the same temperature (usually 20oC but
sometimes 50oC or 100oC) in a standardized
Engler viscosity meter.
Example - Converting
between Kinematic and Absolute
Viscosity for Air
• Kinematic viscosity of air at 1 bar (105 Pa, N/m2) and 40oC is 16.97
cSt (16.97 10-6 m2/s).
• The density of air estimated with the Ideal Gas Law
• ρ =p/RT
• where
• ρ = density (kg/m3)
• p = absolute pressure (Pa, N/m2)
• R = individual gas constant (J/kg K)
• T = absolute temperature (K)
• ρ = (105 N/m2) / ((287 J/kg/K) (273 oC + 33 0C)
•
= 1.113 kg/m3
• Absolute viscosity can be expressed as
• μ = (1.113 kg/m3) (16.97 10-6 m2/s)
•
= 1.88 10-5 (kg/m s, Ns/m2, P)
Different types of Viscosity
Shear-thickening liquids -low viscosity
when stirred slowly, but viscosity increases
when mixed quickly
Shear thinning liquids -high viscosity
when mixed slowly, easier to mix quickly
Bingham liquids -at low stress behaves like
a solid, high stress behaves like a liquid
Granular materials -like Bingham, but do
not have a well-defined viscosity
Types of Fluid on Viscosity Basis
• Newtonian Fluids
• Non-Newtonian Fluids
Continue
Newtonian Fluids
• Fluids for which the shearing stress is linearly
related to the rate of shearing strain are
designated as Newtonian Fluids.
• Newtonian materials are referred to as true
liquids since their viscosity or consistency is not
affected by shear such as agitation or pumping
at a constant temperature. Fortunately most
common fluids, both liquids and gases, are
Newtonian. Water and oils are examples of
Newtonian liquids.
Shear-thinning or Pseudoplastic
Liquids
• Shear-thinning or pseudoplastic liquids
are those whose apparent viscosity
decreases with increasing shear rate.
Their structure is time-independent.
Pseudoplastic Liquids
Grease
Thixotropic Fluids
• Thixotropic liquids have a timedependent structure. The apparent
viscosity of a thixotropic liquid decreases
with increasing time, at a constant shear
rate.
• Ketchup and mayonnaise are examples of
thixotropic materials. They appear thick or
viscous but are possible to pump quite
easily.
Dilatant Fluids
• Shear Thickening Fluids or Dilatant
Fluids increase their viscosity with
agitation. Some of these liquids can
become almost solid within a pump or pipe
line. With agitation, cream becomes butter
and Candy compounds, clay slurries and
similar heavily filled liquids do the same
thing.
Dilatant Fluids
Starch in Water
Bingham Plastic Fluids
• Bingham Plastic Fluids have a yield
value which must be exceeded before it
will start to flow like a fluid. From that point
the viscosity will decrease with increase of
agitation. Toothpaste, mayonnaise and
tomato catsup are examples of such
products.
Bingham Plastic Fluids
Coal Tar
Viscosity and Specific Gravity of
some Common Liquids
Viscosity and Temperature
• Kinematic viscosity of liquids like water,
mercury, oils SAE 10 and oil no. 3 - and
gases like air, hydrogen and helium are
indicated below. Note that
• for liquids viscosity decreases with
temperature
• for gases viscosity increases with
temperature
Umer Zahid
Measurement of viscosity
• Measure flow in thepresence of agradient
of speed
• Poiseuille’s formulafor flow through
acylindrical tubesubject to apressure drop
P
Types of Viscometers
•
•
•
•
•
Redwood Viscometer
Engler Viscometer
Saybolt Viscometer
Ostwald viscometer
Falling-ball viscometer
Redwood
• A standard British-type
viscometer in which the
viscosity is determined by
the time, in seconds.
• Required for a certain
quantity of liquid to pass
out through the orifice
under given conditions
• It is used for determining
viscosities of petroleum
oils.
Working
• The inner cylinder is filled to the marker
level and the outer cylinder filled so as to
have sufficient height to give good heat
transfer.
• The first reading is taken by removing the
stopper from the orifice. The recorded
values were the water and test liquid
temperatures and the time to collect say
50cc of the liquid being recorded.
Conti……………..
• The collected 50cc of liquid must be put back
into the inner cylinder and the used cylinder
inverted to empty completely.
• The level of the sample is checked as, if more of
the liquid is needed it would be added. The
temperature is then raised and the agitator is
used again continuously. This is done until the
liquid is brought within 1 degree of the water
temperature. The same parameters were again
measured. This procedure is repeated for 5
samples in total (at least).
Engler Viscometer
• An instrument used in
the measurement of the
degree Engler, a
measure of viscosity; the
kinematic viscosity ν in
stokes for this instrument
is obtained from the
equation ν = 0.00147t 3.74/t, where t is the
efflux time in seconds.
Working
Saybolt viscometer
• It is Used to determine the
viscosity of petroleum products at
specified temperatures between
70 to 210 °F.
• Stainless steel made, the Saybolt
viscometer is supplied complete
with two interchangeable orifices
Furol and Universal, oil bath,
electric heater with digital
thermoregulator, stirrer, cooling
• Thermometers are not included
and must be ordered separately
Working
Ostwald viscometer
• Need a small-diameter
tube (capillary)
• Measure time of flow of a
specific volume through
the capillary
• Constant pressure drop
across the capillary
• Use Poiseuille’s equation
to calculate viscosity
• Must be calibrated with a
known material
Equation for measurement
Falling-ball viscometer
• Measure the terminal
velocity of a ball
falling in a fluid
• Use Stokes Law for
the viscous drag to
determine viscosity
Equations…
Latest digital viscometers
Continue
Features
• Continuous monitoring of viscosity, and
temperature
• Two 4-20mA outputs for remote recording
• Two analog outputs and RS485 communication
• Compact, explosion-proof systemt
• Automatic self-cleaning
• Readout in centipoises, cSt, or SSU
• Optional LCD display
Installation
Continue
Mohsin Mahmood
Viscosity Application
Oil and Gas
Drilling for oil and gas requires sensitive
viscosity instrumentation, especially at lowshear rates, to insure that production is
optimized.
Continue
• Field viscosity measurements on drilling
and fracturing fluids are required to predict
flow performance under the extremely low.
Industrial Application
• Viscosity
measurement is really
important for industry.
• For correct pump
selection careful
viscosity
measurements are
taken
Continue
• For the transport and storing facilities for fluids
i.e pipes, tanks
Why Measuring Viscosity is
Important For Many Industries
• Nearly all fluids (with the notable exception
of the liquid form of the helium isotopes
helium-3 and helium-4) have some degree
of resistance to flow, with the
measurement being used to determine the
degree of viscosity on a spectrum ranging
from no stress resistance (called an ideal
liquid) to total resistance.
Continue
• Since the temperature of a liquid and its
viscosity are correlated, a viscosimeter or
viscometer must be used in carefully
temperature controlled conditions to
produce accurate results.
Continue
• Even a small change in temperature can
have enough of an effect to negatively
impact the outcome of a quality control
test or production process.
Continue
• Therefore to maintain quality of product,
viscosity is measured step to step at
industries
Industrial Viscometer
Continue
Continue
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