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BASIC CONCEPTS

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Understand the basic concepts of Fluid Mechanics.

Recognize the various types of fluid flow problemsencountered in practice.

Model engineering problems and solve them in a

systematic manner.

OBJECTIVES

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Mechanics: The oldest physical science that deals with both

stationary and moving bodies under the influence of forces.

Statics: The branch of mechanics that deals with bodies at rest.

Dynamics: The branch that deals with bodies in motion.

Fluid mechanics: The science that deals with the behavior offluids at rest (fluid statics) or in motion (fluid dynamics), and theinteraction of fluids with solids or other fluids at theboundaries.

Fluid dynamics: Fluid mechanics is also referred to as fluiddynamics by considering fluids at rest as a special case ofmotion with zero velocity.

BASICS

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Hydrodynamics: The study of the motion of fluids that can beapproximated as incompressible (such as liquids, especially water,and gases at low speeds).

Hydraulics: A subcategory of hydrodynamics, which deals withliquid flows in pipes and open channels.

Gas dynamics: Deals with the flow of fluids that undergo significantdensity changes, such as the flow of gases through nozzles at highspeeds.

Aerodynamics: Deals with the flow of gases (especially air) overbodies such as aircraft, rockets, and automobiles at high or lowspeeds.

Meteorology, oceanography, and hydrology: Deal with naturallyoccurring flows.

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Acceleration 1m/s2 = 100cm/s2

Area 1m2 =104 cm2

Density 1 g/cm3 =1kg/L =1000kg/m3

Energy 1kJ =1000J=1000Nm =1 Kpa.m3

1kj/kg =1000m2/s2

1 kWh=3600kj

Force 1N =1 kg.m/s2 = 10 5 dyne1kgf = 9.80665N

Length 1m =100cm =1000mm= 10 6 m 1 km =1000m

Mass 1kg =1000g 1 ton = 1000kg

Power 1W = 1 J/s 1 KW = 1000w =1kj/s 1 HP = 745.7w

CONVERSION FACTORS

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Pressure 1 Pa = 1 N/m2

1KPa = 1000 Pa = 1/ 1000 Mpa

1 atm = 101.325 kpa =1.01325 bar =

760mm of Hg = 1.03323 kgf/cm2

1 mm Hg = 0.1333kPA

Specific volume 1 m3/kg =1000L/kg=1000cm3/g

Viscosity (dynamic) 1 kg/m.s =1 N .s/m2= 1 Pa.s =10 poise

Kinematic viscosity 1 m2/s = 10 4 cm2/s 1 stoke =1cm2/s

Volume = 1 m3 = 1000 L = 10 6 cm3

Volume flow rate = 1 m3/s = 60,000 L/min = 10 6 cm3/s

CONVERSION FACTORS

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STANDARD ACCELERATION OF GRAVITY

G = 9.80665M/S2

STANDARD ATMOSPHERIC PRESSURE

P (ATM) = 1ATM=101.325KPA

=1.01325BAR=760MM

OF HG =10.3323 M OF WATER

UNIVERSAL GAS CONSTANT

RU = 8.31447KJ/MOL .K = 8.31447KN.M/KMOL.K

CONVERSION FACTORS

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Fluid:A substance in the liquid orgas phase.

A solid can resist an applied shear

stress by deforming.

A fluid deforms continuously under

the influence of a shear stress, no

matter how small.

In solids, stress is proportional to

strain, but in fluids, stress is

proportional to strain rate.

When a constant shear force is

applied, a solid eventually stops

deforming at some fixed strain

angle, whereas a fluid never stopsdeforming and approaches a

constant rateof strain.

Deformation of a rubber blockplaced between two parallel platesunder the influence of a shear force.The shear stress shown is that onthe rubberan equal but oppositeshear stress acts on the upper plate.

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Stress:Force per unit area.

Normal stress:The normal

component of a force acting on asurface per unit area.

Shear stress:The tangentialcomponent of a force acting on a

surface per unit area.

Pressure:The normal stress in afluid at rest.

Zero shear stress:A fluid at restis at a state of zero shear stress.

When the walls are removed or a

liquid container is tilted, a sheardevelops as the liquid moves to re-

establish a horizontal free surface.

The normal stress and shear stressat the surface of a fluid element.For fluids at rest, the shear stress iszero and pressure is the only

normal stress.

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In a liquid, groups of moleculescan move relative to each other,

but the volume remains relatively

constant because of the strong

cohesive forces between themolecules. As a result, a liquid

takes the shape of the container it

is in, and it forms a free surface in

a larger container in a gravitational

field.A gas expands until it encountersthe walls of the container and fills

the entire available space. This is

because the gas molecules are

widely spaced, and the cohesive

forces between them are very

small. Unlike liquids, a gas in an

open container cannot form a free

surface.

Unlike a liquid, a gas does not forma free surface, and it expands to fillthe entire available space.

A li i A f

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Application Areas ofFluid Mechanics

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