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Homework Help: Water flow rate

  1. Dec 11, 2008 #1
    I'm trying to get my head around this question but having missed a few lecture through illness i'm going round in circles.

    Water is fed from a tank 12m above ground along a pipe 200 m long with a diameter of 125mm. Pipe frictyion factor is 0.008. K factors for the fittings, (tank exit, valve etc) add up to 3.3. I'm being asked to find the flow rate in kg/s and donlt knwo where to start.

    I don't want the answer, just some direction of how to approach it.


  2. jcsd
  3. Dec 11, 2008 #2


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    Homework Helper

    Welcome to PF.

    Basically you are going to have the potential energy of the drop (12m) that is given in ρgh that will go into kinetic energy of the flowing liquid that will be 1/2ρV².

    But that's not all it goes into because they have given you the frictional factor that will be experienced over the 120m of run length. And you have the K factor for the pipe system that takes into bends and such that they would give you of 3.3.

    The contribution to friction loss I think looks like

    Frictional resistance energy loss = ½ ρ*f (L/d) x (V²)

    L is Length and d is diameter and f is your frictional factor.

    The K factor contributes an additional energy loss of ½ ρ*K*V²

    where K is your K factor.
  4. Dec 11, 2008 #3


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    Homework Helper

    Here is a lecture that touches on some of the basics. (About 30 minutes in.):

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