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Loss due to contraction vs loss due to expansion

  1. Mar 27, 2016 #1
    1. The problem statement, all variables and given/known data
    why the formula of fricitional pipe loss due to contraction is given by formula : kc(V^2)/2g ?
    why the formula of fricitional pipe loss due to contraction cant be formula : (Va^2)-(Vb^2)/2g ? ,where Va= velocity at inlet , Vb = velocity at outlet ?

    2. Relevant equations


    3. The attempt at a solution
    in this link , i was told that the pressure varies in an unknown and unpredictable way. but , for pipe loss due to expansion , the formula is
    (Va^2)-(Vb^2)/2g ? ,where Va= velocity at inlet , Vb = velocity at outlet ?this make me confused... isn't the pressure also varies in an unknown and unpredictable way in enlarged pipe ?
    https://www.quora.com/Why-is-the-formula-for-the-loss-of-head-in-a-sudden-contraction-of-a-pipe-presented-in-terms-of-velocity-head-in-the-smaller-pipe [Broken]
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Mar 28, 2016 #2

    Simon Bridge

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    Note: Quora is not a scientific source.
    How would you go about modelling the pipe diameter change effect on pressure?
     
  4. Mar 28, 2016 #3
    When the diamter small, velocity high, pressure low
     
  5. Apr 12, 2016 #4
    I was told that the friction loss due to expansion is bigger than the friction loss due to contraction because of flow separation , is it true ? why ?
     
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