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Homework Help: Force on an orifice plate

  1. Mar 19, 2015 #1
    <<Moderator note: Missing template due to move from technical forum.>>

    I am having difficultly with a problem in my fluid mechanics course and I'm hoping someone could help me out.

    Here is a screenshot of the question I'm stuck on:

    So far I have been using Bernoulli equation to find the pressure in the pipe, assuming atmospheric pressure at the point where the stream is released. This gives p1 + 0.5ρv12 = patmos + 0.5ρv22
    Where v2 = v1A1/A2

    I have then been using the Reynolds transport theorem to find the force on the plate:
    m(v2-v1) + p1A1 = PatmosA2 + Fx
    Where m is the mass flow rate, m = ρAv1
    and Fx is the force I am solving for.

    Can anyone find anything wrong with this method, as I have checked my calculations many times but constantly get the wrong answer.

    Thanks in advance
    Last edited by a moderator: Mar 19, 2015
  2. jcsd
  3. Mar 19, 2015 #2
    The signs on some of the terms in the momentum balance are incorrect.

    m(v2-v1)= (sum of forces in +x direction) - (sum of forces in -x direction)

  4. Mar 19, 2015 #3
    Ah, so obvious now... thanks for your help
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