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Calculating Air Flow Within a Pipe

  1. Sep 5, 2010 #1
    Consider a pipe. One end of it (hole) is malleable, in that we can make it larger so that the cylinder adopts a conical shape (yet the other 'hole' does not change).

    If one were to apply suction at one end of the pipe, with respect to air flow, how does the pressure gradient vary within the pipe as the variable hole grows larger?

    In what capacity will centrifugal forces act upon the air flow? (does this suggest a vortex?)
  2. jcsd
  3. Sep 6, 2010 #2


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    Staff: Mentor

    Welcome to PF.

    Could you provide a diagram please - it is very difficult to understand what you are trying to describe.
  4. Sep 6, 2010 #3
    Seems like a horn.
  5. Sep 9, 2010 #4
    Cross-section (pipe is solid & hollow).

    [PLAIN]http://img138.imageshack.us/img138/5590/pipex.png [Broken]

    Assuming suction on the left end, how can we expect the airflow to change as x varies?
    Last edited by a moderator: May 4, 2017
  6. Sep 12, 2010 #5
    Any ideas?
  7. Sep 12, 2010 #6


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    Staff: Mentor

    Yes, as you increase the inlet and the size of most of the pipe, losses will drop so the flow rate will increase as x increases. The maximum flow rate is when the static pressure of the suction is all converted to velocity pressure at the outlet Y and other pressure losses are near zero.
    Through the pipe, you have an inlet velocity that gives you a certain velocity pressure at the inlet and static pressure is atmospheric pressure, then a linear static pressure gradient toward the outlet (suction end). Velocity pressure is constant throughout

    Through the cone, the static pressure again starts at atmospheric and the velocity pressure is near zero, then the velocity pressure increases through the cone and static pressure decreases.
    None that I can see - I don't see a rotational component here.
    Last edited by a moderator: May 4, 2017
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