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Chapter 1-Part 1

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FLUID MECHANICS
chapter 1
Introduction
1.1 Definition of fluid
1.2 Type of fluid
1.3 Fluid properties
Topic Outcomes
• Describe the basic concepts of fluid
mechanics and recognize the various
types of fluid flow problems encountered
in practice
What is a Fluid
?
• A fluid is a substance in the gaseous or liquid
form
• Distinction between solid and fluid?
– Solid: can resist an applied shear by
deforming. Stress is proportional to strain
– Fluid: deforms continuously under applied
shear. Stress is proportional to strain rate
Solid
F
  
A
Deformation of a rubber block
placed between two parallel
plates under the influence of a
shear force.
What is a fluid ?
Stress: Force per unit area.
Normal stress: The normal
component of a force acting on a
surface per unit area.
Shear stress: The tangential
component of a force acting on a
surface per unit area.
Pressure: The normal stress in a
fluid at rest.
Zero shear stress: A fluid at rest is
at a state of zero shear stress.
What is a fluid ?
• A liquid takes the shape of
the container it is in and
forms a free surface in the
presence of gravity
• A gas expands until it
encounters the walls of the
container and fills the entire
available space. Gases
cannot form a free surface
• Gas and vapor are often
used as synonymous words
Intermolecular bonds are strongest in solids and weakest in gases.
Solid: The molecules in a solid are arranged in a pattern that is repeated
throughout.
Liquid: In liquids, molecules can rotate and translate freely.
Gas: In the gas phase, the molecules are far apart from each other, and
molecular ordering is nonexistent.
solid
liquid
gas
On a microscopic scale, pressure is determined
by the interaction of individual gas molecules.
However, we can measure the pressure on a
macroscopic scale with a pressure gage.
Liquid and Gas
• Although liquids and gasses behave in much the
same way and share many similar characteristics,
they also possess distinct characteristics of their
own. Specifically
• -Liquid
• A liquid is difficult to compress and often regarded
as being incompressible.
• A given mass of liquid occupies a given volume
and will occupy the container it is in and form a
free surface (if the container is of a larger
volume).
Liquid and Gas
• Gas
• A gas has no fixed volume, it changes
volume to expand to fill the containing
vessel. It will completely fill the vessel so
no free surface is formed.
• A gas is easily to compress and usually
treated as such - it changes volume with
pressure.
Application Areas of Fluid Mechanics
Fluid dynamics is used extensively
in the design of artificial hearts.
Shown here is the Penn State
Electric Total Artificial Heart.
9
10
11
1–2 ■ A BRIEF HISTORY
OF FLUID MECHANICS
Segment of Pergamon pipeline. Each clay
pipe section was 13 to 18 cm in diameter.
A mine hoist powered by
a reversible water wheel.
12
Osborne Reynolds’ original apparatus for demonstrating the
onset of turbulence in pipes, being operated by John Lienhard
at the University of Manchester in 1975.
13
The Wright brothers take flight at Kitty Hawk.
Old and new wind turbine
technologies north of Woodward,
OK. The modern turbines have 1.6
MW capacities.
14
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