Simple pitot tube experiment

  • Thread starter yessiko
  • Start date
  • #1
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Dear all,

I have a simple experiment to make a cheap pitot tube using 3" PVC pipe to measure vacuum pump air flow. But in the middle of my experiment I have difficulty to calculate air flow in the pipe, because I try to use bernouli equation for standard pitot tube and the result still not same with pump factory refference.

attachment.php?attachmentid=20251&stc=1&d=1251296891.jpg


May some body help me?

Rgrds,

Yessiko
 

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Answers and Replies

  • #2
688
1
Is your pitot tube reading high? There may be an entrance loss on your pitot tube that causes the deviatiation from ideal Bernouli flow.
 
  • #3
FredGarvin
Science Advisor
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Make sure your pitot tube is well aligned with the inlet air flow. Also, chamfer the inlet with a 30° chamfer. This will help with the probe being less sensitive to yaw errors.
 
  • #4
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  • #5
2,985
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Interesting setup. It will be impossible to help you without seeing your actual calculation. I'm guessing you have a unit wrong somewhere.
 
  • #6
FredGarvin
Science Advisor
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The pictures are too small to tell anything.
 
  • #7
Hello
I am undergoing a similar experiment at university and I am making an L shaped simple pitot tube (not pitot static tube). Are there any limits on the dimensions? Such as the ratio of the lenght of the base to the diameter of the tube? I have done research but cannot seem to find anywhere that says anything about that for a simple pitot tube. For a pitot static tube the ratio of 'the distance from the static holes to the 90 degree bend' to the 'diameter of the tube' is best being around 12. But for a simple pitot tube, are there any such limitations?

L shaped simple pitot tube:

|
|
|
|
|
|
'--------
\______/
^
Base
 
  • #8
FredGarvin
Science Advisor
5,066
9
It depends on the flow velocities but a good rule of thumb is to make the base length at least 4 times the tube OD.
 
  • #9
327
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because atmospheric pressure is the pump, not the vacumn, I would think you should need to correct for air density variations real time. A set of "runs" will be relatively meaningless without enviromental conditions being recorded

dr
 

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