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Homework Help: Fluid Mechanics -- Volume flow rate

  1. Jun 15, 2017 #1
    Hey guys. I could use some explanation since I am new to FM: So my problem is the following one: Fluid flows with an average velocity 8 m/s in a pipe with diameter 3m. What is the volume flow rate?
    Now, I think the formula I got to use is Q= v.A Yet, I found my solution from a formula I found on the net where (1/4π * pipe diameter^2 * V). I got my result I need 18π but I just can't understand where I got this formula from and what does it mean! Would be grateful for any assist

    2. Relevant equations

    1/4π * 9 * 8 = 72/4.π or 18π
    Last edited by a moderator: Jun 15, 2017
  2. jcsd
  3. Jun 15, 2017 #2


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    Try putting the π above the divider line instead of underneath .

    What is the formula for area of a pipe of given bore diameter ?
    Last edited: Jun 15, 2017
  4. Jun 15, 2017 #3
    Q=v*A where v is fluid velocity and A is cross-sectional area.

    Restating your formula, Q=v*(D2π/4) where D is diameter. An equivalent formulation is Q=v*(r2π) where r is the pipe radius. The way I think of it is,
    • "How much volume fits into a pipe one meter long?" 1 meter of length times the cross-sectional area (r2π) is, in this case, 7.068 m3.
    • "How many of these volumes pass through the pipe per unit time? In this case, it is 8 linear meters per second multiplied by the volume contained within a meter of that diameter pipe.
    << Solution deleted by Mentor >>
    Last edited by a moderator: Jun 15, 2017
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