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Fluid mechanics q

  1. Oct 28, 2005 #1
    Ok guys, heres a q from a past exam and Im not sure how to tackle it.
    At point C, there is a leak and flow rate is given in L/s. I am also given the friction factor. I also know the diameter of the pipe.

    The question asks for the vol. flow rate into the bottom tank. And then the head loss in BC and CD

    What Im unsure of is the steps I need to take with Bernoullis equation. ie apply at AB then BC etc. I dont get that bit.

    So if someone could point me in the right direction, Id be very happy.


    Attached Files:

  2. jcsd
  3. Oct 30, 2005 #2
    Ok, so I think Ive calculated the volumetric flow rate, but it came out to be 3535 L/s, which is a fair bit for a 22cm diameter pipe.

    I now have to find the head loss in BC and CD, but I dont know how to do this since I dont know the pressure at C.

    Finally I have to sketch the hydraulic gradient, which Ive never even heard of before.

    Anyone have any ideas about these last bits?
  4. Oct 30, 2005 #3


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    Is the top reservior an open reservoir? Do you know the height at point C? That would mean that the pressure at C should be a combintation of the velocity head and the potential head at point C while the pressures at A and E are 0.

    http://www.engineeringtoolbox.com/energy-hydraulic-grade-line-21_613.html [Broken]

    also, check out the definition on page 47 here:
    http://www.engineeringtoolbox.com/energy-hydraulic-grade-line-21_613.html [Broken]
    Last edited by a moderator: May 2, 2017
  5. Oct 30, 2005 #4
    Both reservoirs are open to the atmosphere.

    I dont know the height of C. Normally, finding pressure at C wouldnt be a worry, but this time there is a leak at C.

    So would the pressure be the velocity head (With leak taken into account) plus potential head?

    Thanks Fred!
  6. Oct 31, 2005 #5


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    Since it appears that that is the only information you have to go on, then I would say that you are correct. You should have some potential head, but if you are not given that information, then it might as well be considered insignificant. Velocity head is all you have left.
  7. Nov 1, 2005 #6
    Cheers Fred.
  8. Nov 1, 2005 #7


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    Did it come out OK? Hope I helped.
  9. Nov 1, 2005 #8
    Yeah came out eventually. :)

    I think Ive been letting the algebra get in my way, instead of letting my head look at the particular question. Hope theres an easy example of this question on the exam. :)
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