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Hydraulics and the darcy weisbach formula

  1. Oct 5, 2008 #1
    I am a hydraulics student and have a question, hoping someone here could help me out. In my specific assignment i am required to determine D of a pipe without the friction factor using moody diagram and the darcy-weisbach equation.

    here is the exact question:
    A steel pipe (e=0.065mm) 4200m long is to convey oil (kinematic viscosity=5.2x10^-5 m/s^2) at 300 L/s from a resevior with surface elev. 247m to one with surface elev 156m. Theoretically, what pipe diameter size is required?

    All the prof says is Iteration is required to find pipe diameter.

    Any thoughts? anybody?

  2. jcsd
  3. Oct 6, 2008 #2
    Write an energy balance (Bernoulli equation). The driving head (the difference in elevation from one end to the other) creates a flow rate (velocity) that results in friction pressure loss that balances the driving head. So, you have to guess a flowrate and iterate. Does that make sense?
  4. Oct 6, 2008 #3
    I would probably do the same as gmax137 suggested.

    My step by step approach would be

    1) Use Bernoulli to get an estimate of Q (ie Q if there was no friction in the system)
    2)from the estimate of Q, find your Re and hence get a value for f
    3)calculate a new Q and continue to iterate between (2) and (3) until your answer converges.

  5. Oct 9, 2008 #4


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    See page 14 (equations 15 and 16) on the attached.
    (click on the link to my post to find the attachment "Pipe-Flo Pro.pdf"
    Last edited: Oct 9, 2008
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