Fluid flow (liquid) concept with viscosity.pdf

Viscous flow in fluid mechanics

1. 1
Fluid Dynamics
–
V
iscosity
Dave Foster Dave Foster Department of Chemical Engineering Department of Chemical Engineering University of Rochester University of Rochester Email: Email:
dafoster dafoster
@@
cheche
..
rochester rochester
..
eduedu

2. 2
Chemical Engineering What do Chemical Engineers Do? „„
Manufacturing Manufacturing
„„
Research Research
Chemical
Biotech
Medical
Pharmaceutical

3. 3
OK, first a little background „„
Fluid Mechanics is the study
of fluids either in
Fluid Mechanics is the study
of fluids either in
motion (Fluid Dynamics) or at rest (Fluid Statics) motion (Fluid Dynamics) or at rest (Fluid Statics)
„„
Fluids are either gas or liquid Fluids are either gas or liquid
„„
Solids are NOT fluids Solids are NOT fluids
„„
Properties of the fluid are things like density, Properties of the fluid are things like density, pressure, temperature, and pressure, temperature, and
VISCOSITY VISCOSITY
!!

4. 4
Fluid –
a
definition
„„
A substance that deforms continuously under A substance that deforms continuously under the action of shear stress the action of shear stress
‹‹
Gas or Liquid Gas or Liquid
‹‹
Solids can resist a shear stress, a fluid can Solids can resist a shear stress, a fluid can
’’
tt

5. 5
Applications of Fluid Mechanics „„
Explains Explains
blood flow
in capillaries of a few in capillaries of a few
microns in diameter to
crude oil flow crude oil flow
through an 800 mile long, 4 ft diameter pipe through an 800 mile long, 4 ft diameter pipe
„„
Explains why Explains why
airplane
ss
are streamlined are streamlined
with smooth surfaces with smooth surfaces
„„
Explains why Explains why
golf balls
are made will are made will
dimpled surfaces for most efficient travel dimpled surfaces for most efficient travel

6. 6
Effect of Dimples on Golf Balls
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
100
200
300
400
V
e
l
o
c
i
ty (F
e
e
t p
e
r
S
e
c
o
n
d
)
Drag (Pounds of Force)
Dr
a
g
f
o
r
Sphe
r
e
D
r
ag f
o
r
G
o
l
f
Bal
l

7. 7
A List of Some Applications „„
Coating Coating
„„
Breathing Breathing
„„
Blood flow/pipe flow Blood flow/pipe flow
„„
Swimming Swimming
„„
Pumps (traditional and Pumps (traditional and your heart) your heart)
„„
FansFans
„„
Turbines Turbines
„„
Airplanes & Rockets Airplanes & Rockets
„„
Missiles Missiles
„„
Ships Ships
„„
Kidney dialysis machines Kidney dialysis machines
„„
Heart Heart
--
Lung bypass Lung bypass
machines machines
„„
Membrane Membrane
oxygenators oxygenators
„„
Engines Engines
„„
And lots more! And lots more!

8. 8
For everything “FLUID”
-
„„
Flow is key Flow is key
‹‹
How fast How fast
‹‹
What direction What direction
‹‹
How changing with time (differential How changing with time (differential equations) equations)
„„
Flow properties deal with things like the Flow properties deal with things like the velocity, changes in temperature, velocity, changes in temperature, concentration. concentration.

9. 9
Isaac Newton „„
Key player in much of basic science Key player in much of basic science
„„
Three Three
““
LawsLaws
””
1.1.
A body will remain at rest or in motion A body will remain at rest or in motion unless acted upon by an external force unless acted upon by an external force
2.2.
ΣΣ
F = m a F = m a
3.3.
For every action there is an equal and For every action there is an equal and opposite reaction opposite reaction

10. 10
Newton’s Law of Viscosity:
dydv
µ
τ
=
Shear stress
viscosity
Shear Strain

11. 11
Viscosity –
W
hat is it?
„„
A property of a fluid to resist the rate of A property of a fluid to resist the rate of deformation deformation
––
a quantitative measure of a fluid a quantitative measure of a fluid
’’
s s
resistance to flow (water vs. syrup) resistance to flow (water vs. syrup)
„„
Takes place when a fluid is acted upon by a shear Takes place when a fluid is acted upon by a shear stress stress
„„
Simply stated, it Simply stated, it
’’
s how s how
““
thick thick
””
a fluid is a fluid is
‹‹
We easily move through air We easily move through air
‹‹
ItIt
’’
s more difficult to move through water which s more difficult to move through water which
is 50X higher in viscosity than air is 50X higher in viscosity than air

12. 12
A couple common examples: Air < Water < Paint < Pancake Syrup < Tooth Paste Air < Water < Paint < Pancake Syrup < Tooth Paste
Least Viscous
Most Viscous

13. 13
Units
(yep –
units, very important)
„„
If we talk about how deep a If we talk about how deep a swimming pool is and I tell you swimming pool is and I tell you that it that it
’’
s s
““
1010
””
, would you dive in? , would you dive in?
„„
Not if it Not if it
’’
s 10 inches s 10 inches
„„
But you might if it was 10 feet But you might if it was 10 feet
Units are key in all of science, never Units are key in all of science, never accept a number without a unit if it accept a number without a unit if it
’’
s s
supposed to have one supposed to have one

14. 14
Units of Viscosity „„
Poise (the most common units used to Poise (the most common units used to describe viscosity, but not the only one) describe viscosity, but not the only one)
„„
Named after the French physician Named after the French physician
––
Jean Louis Poiseuille (1799 Jean Louis Poiseuille (1799
--
1869) 1869)
„„
OneOne
--
hundredth of a Poise is a centipoise or hundredth of a Poise is a centipoise or
““
cPcP
””

15. 15
Viscosity of Some “Common”
Materials
(all are in units of Centi-Poise)
Hydrogen Hydrogen
0.0088 0.0088
Carbon Dioxide Carbon Dioxide
0.015 0.015
Air Air
0.018 0.018
Blood Blood
0.400.40
Gasoline Gasoline
0.290.29
Water Water
1.01.0
Mercury Mercury
1.51.5
Corn Oil Corn Oil
7272
SAE 30 oil SAE 30 oil
290290
Heinz Ketchup Heinz Ketchup
50,000 50,000

16. 16
Changing a Material’s Viscosity „„
Easiest ways: Easiest ways:
‹‹
Change the Temperature Change the Temperature
––
Heat it Up ! Heat it Up !

Strong Effect Strong Effect
‹‹
Change the Pressure Change the Pressure
––
not as easy not as easy
……

Weak Effect: Decrease pressure, viscosity Weak Effect: Decrease pressure, viscosity decreases decreases

17. 17
In a perfect world: „„
Fluids obey Newton Fluids obey Newton
’’
s Law of Viscosity s Law of Viscosity
Straight line passing through the origin
dydv
µ
=
τ
Slope = viscosity
τ
(Format: y = m x + b)
dv/dy

18. 18
Newtonian Fluids „„
Fluids that obey Newton Fluids that obey Newton
’’
s Law of Viscosity s Law of Viscosity
„„
Linear relationship between shear stress and Linear relationship between shear stress and shear strain shear strain
„„
Some Examples of Newtonian Fluids: Some Examples of Newtonian Fluids:
‹‹
Water Water
‹‹
Simple Alcohols Simple Alcohols
‹‹
Simple Organic Solvents Simple Organic Solvents

19. 19
Everything Else is a
Non-Newtonian Fluid

20. 20
Non-Newtonian Fluids „„
Examples: Honey, toothpaste, paint, blood, Examples: Honey, toothpaste, paint, blood, ketchup, syrup, many polymers ketchup, syrup, many polymers
The list goes on and on The list goes on and on
………………

21. 21
Non-Newtonian Fluids
Newtonian
Dilatant –shear-thickening- fluid increases resistance
with
Increasing applied stress (ex. Rarely encountered, Cornstarch + water, Silly putty)
Pseudoplastic –
s
hear-thinni
ng-
Fluid decreases resistance with increasing stress. (ex: hai
r
gel)
τ
dv/dy

22. 22
Why do we care? „„
The primary parameter correlating the The primary parameter correlating the viscous behavior of Newtonian Fluids is the viscous behavior of Newtonian Fluids is the dimensionless Reynolds Number: dimensionless Reynolds Number:
viscosity
distance
*
velocity
Re
=

23. 23
Why do we care? „„
The first thing a fluids researcher should do The first thing a fluids researcher should do is estimate the Reynolds Number range of is estimate the Reynolds Number range of flow under study. flow under study.
‹‹
Low Re = laminar flow Low Re = laminar flow
(no change with time) (no change with time)
‹‹
High Re = turbulent flow High Re = turbulent flow
(changes with time) (changes with time)

24. 24
Reynolds Number and Viscosity
Viscosity Re Viscosity Re Viscosity Re Viscosity Re
viscosity
distance
*
velocity
Re
=

25. 25
How can we use Viscosity (and Fluid Dynamics)? „„
Flow measurements in human body Flow measurements in human body
‹‹
Heart valve flow volumes Heart valve flow volumes
„„
Coating technologies Coating technologies
‹‹
Lots of applications Lots of applications
„„
Moving fluids from one place to another Moving fluids from one place to another
‹‹
Blood flow in your body Blood flow in your body
‹‹
Chemicals in pipes Chemicals in pipes
„„
Moving objects through fluids Moving objects through fluids

26. 26
Thanks !! Thanks !!
Any Questions ? Any Questions ?