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How to find the flow rate trough a pipe using pressure drop

  1. Feb 4, 2010 #1
    I wanna know how high the flow rate trough a pipe is (outlet), but I only now the pressure difference (0.7MPa or 7 bar), and the diameter of the pipe.

    At what speed (or for that matter volume) does air leave a pipe when the pressure difference is 7 bar, and the diameter is 25.4mm?

    If it makes any difference it's steel pipes, of about 50 meters. (But I don't feel that info is neccesary)

    Thanks a lot in advance!
  2. jcsd
  3. Feb 4, 2010 #2
    For a first approximation you can use this formula for the velocity.

    V = sqrt(2*g*dp/dens)


    g = gravitation acceleration
    dp = pressure drop
    dens = density of fluid in the pipe line.

    Make sure all of your units cancel correctly.

    Yes, it does make a difference because of the relative roughness of the pipe. This value is needed in order to calculate the correct friction factor.

    This would be necessary if you where trying to size the pump needed to pump the fluid the 50 meters.

    Hope that helps.

  4. Feb 4, 2010 #3
    Excellent answer!

    I guess I could've phrased my question a little better.

    At what speed does the air leave the outlet when you know it holds 7 bars in the pipe?

    Thanks a lot for the quick response :)

    (Anyone know a page where I can find general forumlas regarding compressed air?)
    Thanks in advance.
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