PROPERTY OF PRESSURE z (m) Pressure the same in all directions P= gz Pressure always perpendicular...
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Transcript of PROPERTY OF PRESSURE z (m) Pressure the same in all directions P= gz Pressure always perpendicular...
PROPERTY OF PROPERTY OF PRESSUREPRESSUREz (m)
Pressure the same inall directions P=gz
Pressure always perpendicular to a surface.
A B
Pressure the same at A and B.
ABSOLUTE- ,GAGE PRESSURE
Vacuum: 0 N/m2 (Pa)Atmospheric pressure (Patm): 1.013 . 105 N/m2
(Pa)Gage pressure (Pgage): Pressure reading at gageAbsolute Pressure (Pabs): Pabs=Patm+Pgage
Patm=101 kPa
Ex Pabs=151 kPa Pabs=51 kPa
Pabs=151
Pgage=50 kPa
Pabs =51 kPa
Pgage= -50 kPa
Pabs=0
Pgage=0Patm=gage reference
Pabs=0
PIEZOMETRIC HEADPressure head h=P/ (m) h
Piezometric headThe sum of the elevation abovean arbitrary datum plus thepressure head.H= h + z = P/ + z
hP
z z
P
PRESSURE MEASUREMENTS
a
h (m)
a
Piezometer/Manometer
Gage pressure at surface = 0 Pa=0+ . h
Ex: Calculate the heigth (h) of the water column if thepressure at point a is 50 kPa.
PRESSURE MEASUREMENTS
U-TUBE/DIFFERENTIAL MANOMETER
a a
a
h1h2
Pa=0+h1 . mercury - l1 . H2O
l1
Pa=0-h2 . mercury - l2 . H2O
l2
Manometer liquid:mercury
EXAMPLE U-TUBEEXAMPLE U-TUBE
a a
h1h2
l1
Calculate the gage - and absolute pressure in the pipes. mercury=13600 kg/m3 . The atmospheric pressure is 100 kPa.a)h1=10 cm ; l1=0.3 m b)h2=1 cm ; l2=0.4 mc) Calculate h if the manometer liquid is water in a).
l2
a
l1
h
DIFFERENTIAL MANOMETER
h
a bl1 l2
Calculate the pressure difference between b and a.h=1.5 cml1=30 cmmercury=13600 kg/m3
Pa Pb
Manometer liquidmercury
EXAMPLE
water
0.5 m
1.5 m
2.5 m
airoil
1.4 m
0.4 m
Calculate the gage pressure of air.oil=900 kg/m3
mercury=13600 kg/m3
Manometer liquid:mercury