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Pipe pressure drop calculation

  1. Feb 10, 2013 #1
    I am calculating various pressure drops in a pipe and am and am having trouble calculating the pressure at a certain point, for a set case. This is the pipe...


    A and B are vents, through which air passes and travels on up the pipe, where is it discharged to atmosphere. I am working out the pressure at points a and b for three cases.

    1) both vents open and pumping air
    2) vent A open, vent B closed
    3) vent A closed, vent B open

    I have worked everything out no bother for cases 1 and 2 but 3 is stumping me. My engineering brain knows that there should be a vacuum effect at a, because of the flow through b onwards, but I can't work out how to do the calculation. So far, setting the flow rate at a to zero just makes the frictional losses zero at this point, and leaving it at the same pressure as at b ... which isn't right!

    I have accounted for losses due to the fittings (inlets) in my calculation.

    I would like to know a method to calculate pressure at a when vent A is closed.

    Thanks in advance.
    Last edited: Feb 10, 2013
  2. jcsd
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