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Help me calculate venturi flow rate

  1. Jul 24, 2012 #1
    Hi I have a challenge (Its over 30 years since I did physics). I have the following information and I want to calculate the flow rate change .

    Opening diameter 2m , narrows smoothly to diameter 1m. Seawater, tidal flow of 2.5 m/s into the opening, what is the effective flow rate in the throat of the venturi
     
  2. jcsd
  3. Jul 24, 2012 #2

    tiny-tim

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    welcome to pf!

    hi declanka! welcome to pf! :smile:

    water is incompressible, so the flow rate (volume per second) must be constant, so the speed (metres per second) must be inversely proportional to cross-section area :wink:

    (and in this case, the area is 1/4, so the speed must be x 4)
     
  4. Jul 25, 2012 #3
    Thanks for this response, it logically confirms the calculations I came up with. Is the formula always true , even in the scenario where its just an open venturi (narrowing) pipe facing into the tidal flow .
     
  5. Jul 25, 2012 #4

    tiny-tim

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    yes, it's conservation of mass …

    the water can't bunch up anywhere, or thin out, so the flow into any part of the pipe must be the same as the flow out of it … ie the flow rate (volume per second) past any two cross-sections must be the same
     
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