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Work to close valve

  1. Jan 26, 2013 #1
    Hey!
    Yesterday I was on the Czech Physics Olympiad. There were many examples. To one, however, I did not invent anything, because I don't learn Hydrodynamics to much.
    I want to understand it better, so I want to ask you how you calculate it, please. I'm sorry, I did not give my progress here, but I have not it, because I do not know much about Hydrodynamics. I spent two hours thinking but I did not invent it.

    So... example:

    Liquefied gas flowing in a pipeline. You want to close the pipeline. To close the pipeline you must close a valve (move plate across pipeline).
    - in a large reservoir, where pipeline is connected, the pressure is 2 MPa
    - valve (plate) has a thickness 10 cm
    - pipe has a square cross section with a side length 1 m
    - liquefied gas has a density 480 kg/m3 and and flow 20 m3/s

    What is the value of work to close the valve?

    Thanks... And if you don't understand me, write, i will try to write it better.
     
  2. jcsd
  3. Jan 26, 2013 #2

    Simon Bridge

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    Imagine the valve is half closed - what does the system look like?
     
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