1. MET 212
Fluid Mechanics
Lecture # 3
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2. Objective
 Fluid Pressure
Pressure at Point
 Basic Equation For Pressure Filed
Incompressible Fluid
Compressible Fluid
Example
Pressure Measurement
Manometer
 Piezometer Tube
 U-Tube Manometer
 Inclined-Tube Manometer
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3. Fluid pressure
Pressure at Point
z
p s x s
x
θ
s
p y x z
y
z`
y
θ
 x y z
x
 p z x y
2
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6. Basic Equation For Pressure Filed
dp
 
dz
This equation indicate that the pressure gradient in vertical direction is negative
that is the pressure decrease as we move upward in the fluid at reset
Incompressible Fluid
 ( ρ ) constant
 ( g )in most of fluid application is neglected
P1   h  p 2
Compressible flow
( ρ ) is not constant
 p   RT
 g ( z 2  z1 ) 
P2  p1 exp   
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 RT 0 

7. Basic Equation For Pressure Filed
Open
Example
A tank has a gasoline and water as shown in the
Figure. If the SG of gasoline is 0.68 determine the
pressure at the gasoline water interface and at the 17 ft
bottom of the tank Gasoline
Water 3 ft
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8. Pressure Measurement
Manometer
Manometer has three types:
Piezometer Tube
U-Tube Manometer
Inclined-Tube Manometer
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9. Piezometer Tube
PA   1 h1
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10. U-Tube Manometer
p A   2 h 2   1 h1
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11. U-Tube Manometer
Example
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12. U-Tube Manometer
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13. Oil
Mercury
h ?? m
0.17
0.2 m
A
+
h? m
0.3
Water
B
+