Flow of air in a pipe

  • Thread starter Karol
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  • #1
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Homework Statement


air flows in a 4" pipe. at point A a 2[bar] pressure was measured and the temperature was 22°C. the velocity V1was 5[m/sec].
At point B, down the stream, a 1.2[bar] pressure was measured and the temperature was 32°C.
What is the velocity V2at point B.

Homework Equations


The continuity equation:
[itex]\gamma[/itex]1A1V1=[itex]\gamma[/itex]2A2V2
Where [itex]\gamma[/itex]=specific gravity, A=section area.

The gas law:
pv=RT
Where: p=absolute pressure
[itex]v=\frac{1}{\rho}[/itex], [itex]\rho[/itex]=specific mass


The Attempt at a Solution


The specific gravity at point A:
[tex]\gamma_1=10\frac{2E5}{287\cdot 295}=23.6[N/m^3][/tex]

The specific gravity at point B:
[tex]\gamma_2=10\frac{1.2E5}{287\cdot 305}=13.7[N/m^3][/tex]


The continuity equation, without the area, since it's the same on both points:
[tex]23.6\cdot 5=13.7\cdot V_2 \Rightarrow V_2=8.6[/tex]
The answer should be 7.05.
 

Answers and Replies

  • #2
TSny
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Are the measured pressures "gauge pressures"?
 
  • #3
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the problem statement is exactly as written in the book.
Maybe they should be, but that's the books mistake.
 
  • #4
TSny
Homework Helper
Gold Member
13,361
3,619
the problem statement is exactly as written in the book.
Maybe they should be, but that's the books mistake.

Well, measurements of pressure are often gauge pressures. See what you get for the answer if you assume they are gauge pressures :smile:
 
  • #5
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yes, thank you, it solved. bye
 

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