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HYDRAULICS: CWR 3201
SPRING 2012
LECTURE 1
INTRODUCTION & PROPERTIESOF FLUID
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FLUID PROPERTIES
-Definition: Fluid has certain characteristics by which itsphysical properties are described.
-These properties expressed in terms of length, mass, force,
time temperature.
-The traditional system of unit in US is ft-lb-s system.
-SI system: kg-m-s system.
-This course will use both SI & traditional units
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BASIC UNITS
SI Unit:
-Mass: kg, Length: m, Time: s
-Force: Newton= 1kg x 1m/s2
-Temperature: Kelvin K= 273+ oC
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BASIC UNITS
SI Unit:
-Work or Energy: Joule (J)= N.m (Force x Distance)
-Power: Watt= Joule/s
-Prefixes: -G (giga) = 109 c (centi) = 10-2
-M (mega) = 106 m (milli) = 10-3
-K (kilo) = 103 (micro) = 10-6
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BASIC UNITS
FPS System / US Customary Units:
-FPS (Foot-Pound-Second)
-Mass: lbm
, Length: ft, Time: s
Also,
-Mass: slug (14.59 kg),
-Force: lbf= 1slug x 1ft/s2
-Conversion: 1 slug = 14.59 kg x (1 lbm / 0.453 kg) = 32.2 lbm
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Properties Involving Mass or WeightMass Density ():
Mass per unit volume.
Mass density of water = 1000 kg/m3 or 62.4 lbm/ft3
Specific Weight ():
Gravitational force per unit volume
Specific weight of water is 9.8 kN/m3
Specific Gravity (S):
Ratio of specific weight of a fluid to the specific weight of water.
V
m
g
Water
Fluid
Water
FluidS
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EQUATION OF STATE & DENSITY OF GASESIdeal Gas Law:
p= Absolute Press.; V= Volume, n= Number of moles,Ru=Universal gas constant, T= Absolute temperature
Eqn may be rewritten as
M= molecular wt. of the gas. The product of number of molesand molecular wt. is the mass of the gas.
Ru/M= R, is the gas constant
TnRpV u
TM
R
V
nMp u
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EQUATION OF STATE & DENSITY OF GASESSo the Equation of State becomes
Or mass density of gas
* Problem (Handout)
RTp
RT
p
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VISCOSITY
-Viscosity (also called dynamic or absolute viscosity):-Measure offluids resistance to deformation under shear stress.
-Shear stress proportional to time rate of strain
-Unit: Poise= 0.1 N.s/m2
-Viscosity of water @ 20oC is 1 CP (10-2 poise)
* Problem (Handout)
dydV
2
2
/./)/(
/
/msN
msm
mN
dydV
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VISCOSITY-Kinematic Viscosity
smmkg
msN/
/
/. 23
2
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NEWTONIAN VS. NON-NEWTONIAN FLUIDS
Newtonian FluidShear stress is directly proportional to rate of strain
Non-Newtonian Fluid
Shear stress is NOT directly proportional to rate of strain
-Shear-thinning fluids: decreases with
-Shear thickening Fluids: gypsum in water
-Bingham plastic: Acts like solid
dy
dV/ dy
dV
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SURFACE TENSION
-Property by which a liquid at a material interface exerts a force per unitlength along the surface
- Due to Molecular attraction
-Produces a surface that acts like a stretched membrane.
-The tension that acts on the plane of surface is calculated by:
F = L L=Length over-which the surface tension acts
-Capillary action shows the effect of surface tension
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PRESSURE
Pressure:
- Ratio of normal force to area at the point.
- Scalar quantity: Only magnitude
Units:
- SI: N/m2 (Pascal)- Traditional unit: psi, psf
- Engineers frequently states the pressure as height of column of liquid (ft,inch, m)
- Example: 50 psi= 127 ft of water column or just 127
dA
dF
A
FLimp normalnormalA
||
0
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ABSOLUTE PRESSURE, GAGE PRESSURE,
VACUUM PRESSURE
Absolute Pressure:
- Pressure measured relative to zero pressure
- Pressure in perfect vacuum is called zero pressure
- Absolute pressure is referenced to regions such as outer space (region is
devoid of gas)
Gage Pressure:
-Pressure measured relative to prevailing to atmospheric pressure
-e.g.: Gage pressure 50 kPa recorded at a place, where atmospheric press.=
100 kPa then that pressure can be expressed as
p= 50 kPa gage or p= 150 kPa abs
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ABSOLUTE PRESSURE, GAGE PRESSURE,
VACUUM PRESSUREVacuum Pressure:
-Difference between atmospheric press. & actual press.
-When press. is less than atmospheric, press. can be described as vacuum
press.
Standard Atmospheric Pressure at sea level
1 atm = 101.3 kPa = 14.7 psi = 33.9water = 760 mm Hg = 2116 psf
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ABSOLUTE PRESSURE, GAGE PRESSURE,
VACUUM PRESSURE
Relationship
Example
gageatmabs PPP
vacuumatmabs
PPP
gagevacuum PP
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PRESSURE MEASUREMENT
Five scientific instruments:
- Barometer
- Bourdon-Tube Gage
- Piezometer
- Manometer
- Pressure Transducer
Today
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PRESSURE MEASUREMENT
Barometer- Measure atmospheric pressure.
- Mercury barometer
-What is atm. press (kPa) when h=760 mm (SHg= 13.6)
- Aneroid barometer: Works mechanically
hphp HgvHgatm
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PRESSURE MEASUREMENT
Bourdon-Tube Gage
Measures pressure by sensing deflection of a coiled tube.
Performed lab experiment