fluid mechanics

1. Fluid Statics: Pressure intensity and
pressure head: pressure and specific weight
relationship, absolute and gauge pressure
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FLUID MECHANICS

2. Fluid Statics
C Fluid Statics: It is the branch of fluid mechanics that deals
with the behavior/response of fluid when they are at rest.
C Pressure, (average pressure intensity):It is the normal force
exerted per unit area. It is denoted by P and is givenby;
C Units
C N/m2 (called Pascal)
C lb/ft2 or lb/in2 (calledpsi)
P 
force

F
area A
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3. Pressure vs Water depth/height
C Consider a strip or column of a cylindrical fluid,
C h= height or depth of strip of fluid
C γ= specific weight of fluid
C dA=cross-sectional area of strip
C dV=volume of strip
C dW=weight of strip
C Pressure at base of strip=dF/dA=dW/dA
C
C
P= γdV/dA
P= γdA.h/dA
P=γh
h
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4. Pressure vs Water depth/height
C P=γh
C P α h
C For h=0,P=0
C For h=h,P=γh
h
Pressure distribution
diagram/pressure profile
C As you know atmospheric pressure reduces, as we move to
higher elevations. Is it because of h, as h reduces, P also reduces.
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5. Absolute and Gauge Pressure
C Atmospheric pressure
C Gauge pressure
C Vacuum/negative pressure
C Absolute pressure
C Atmospheric pressure: Pressure exerted byatmosphere
C Gauge pressure: Pressure more than atmosphericpressure
C Vacuum/negative pressure: Pressure less than atmospheric pressure
C Absolute pressure: Pressure measure relative to absolutezero
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Pabs Patm Pvac
 Pg
Pabs Patm

6. Atmospheric Pressure
C It is defined as weight of air per unit
surface area of earth.
C Standard atmospheric pressure at
mean-sea-level is
=101.3KN/m2
=1.013bar
=14.7psi
=760mm of Hg
=33.9ft of water
=10.3m of water
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7. Measurement of Atmospheric Pressure
C Barometer: It is device used
to measure the atmospheric
pressure at any point on the
earth.
C Types of barometer
Liquid barometer
C It measures the pressure with
help of column of liquid
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8. Liquid Barometer
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C Generally,mercury is preferred liquid because its vapour pressure is
minimum.Moreover, its specific gravity is very high so that size
(height) of barometer required is small.
C However, for other liquid vapour pressure must be considered in
estimation.
C The barometer using mercury is called mercury barometer and
while using water is called water barometer.
C Size of barometer tube should be more than ½ inches (or 13mm)
to avoid capillarity.