Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fluids problem should be simple

  1. Jun 23, 2014 #1
    Hi everyone.

    So i have a simple problem and its really confusing me, although i think i might have been starring at the page too long.

    I have a pipe which has 4 inlets and one outlet; via air being pulled through via a centrifugal pump. Think of the inlets as pulling air from atmosphere like in an air conditioning unit

    The single outlet is 360mm diameter which is flowing at 15 m/s.

    2 of the inlets are 125mm diameter
    the other 2 are 150 mm diameter

    Using basic continuity and mass balance is it possible to determine the flow rates?
    I'm guessing it could be a simple ratio problem?

    If they were all the same diameter (say 125) it would be simple as the flow would be the same at each inlet (31.1 m/s)

    Please help me out, thanks.
  2. jcsd
  3. Jun 24, 2014 #2


    User Avatar
    Science Advisor

    Welcome to PF.
    You seem to be making an assumption that the pipe has infinite diameter. The flow, through the inlets, must combine in some way before reaching the outlet. That internal flow variation within the pipe will invalidate your assumption.

    Maybe you are looking at it from outside, as a simple big box with 5 circular ports. It might be better to invert your view, then look at internal network flow, with 5 fixed pressure, circular ports.
  4. Jun 29, 2014 #3
    Pls find the attached solution. Couldn't type the entire thing.. :tongue:

    Attached Files:

    • pipe.jpg
      File size:
      21.5 KB
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook