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1
Do you still remember?
• Fluid
• Mechanics
• Fluid dynamics
• Fluid statics
• Stress – tensile, compressive, shear
• Shear force, shear strain
• Newton’s law of viscosity
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• Ability to resist deformation?
If
YES
let’s move on……….
Lecture 2 Week 1
Fluid Properties
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Viscosity & kinematic viscosity
Density, Specific volume, Specific weight, Specific gravity
Surface tension, Pressure

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Viscosity
Property that determines the amount of resistance to shear force.
Due primarily to interaction between fluid molecules
F
y
U
V
Fluid
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Fluid is filled between plate
To keep plate moving at constant velocity, U
a constant force, F must be applied
Viscosity
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y
AU
F
α
dy
dV
A
F
α
dy
dV
α
τ

3
Viscosity
dy
dV
μ
=
τ
Coefficient of
viscosity
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viscosity
(dynamic viscosity)
Viscosity
d
dV
μ
τ
=
Newton’s law of viscosity
Shear stress is linearly proportional to the velocity gradient
dy
=
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⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
dy
dV
μ = f (types of fluid, time and T)

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Types of fluids
Newtonian fluids
Fluids that obey Newton’s law of viscosity
Non-Newtonian fluids
Fluids that do not obey Newton’s law of viscosity
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Fluids that do not obey Newton s law of viscosity
μ
varies with
types of fluid
•
Newtonian fluids
•
τ
is
proportional
to dV/dy
•
All gases
•
All liquids having simple
chemical formula
– E.g: H
2
O, CH
3
OH, C
6
H
6
•
Most dilute solution of
simple molecules in water or
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simple molecules in water or
organic solvents
– Metal ion solution, sugar
in water

5
Newtonian fluids
Straight line through origin
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•
Non-Newtonian fluids
μ
varies with types of fluid
• Shear stress is
a
function
of
the velocity
gradient.
(viscosity is not a
constant)
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•
Bingham fluids
• Resist small shear stress.
• Flow easily under larger
μ
varies with types of fluid
shear stress
(Force must be given in
order to move the fluid)
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• Pseudoplastic
fluids
• Shear thinning fluids
μ
varies with types of fluid
•
viscosity decreases with
increasing rate of shear
stress
•
μ
o
as dV/dy
m
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A shear thinning fluid decreases in
viscosity with
increasing shear rate

7
•
Dilatant fluids
• Shear thickening fluids
μ
varies with types of fluid
•
μ
m
as dV/dy
m
• E.g. Starch suspension,
printing ink
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μ
varies with
time
Viscosity is time independent
All Newtonian fluids are
time independent
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Most of non-Newtonian fluids
are time dependent

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