Help me calculate venturi flow rate

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declanka
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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
 
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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)
 
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 .
 
declanka said:
Is the formula always true , even in the scenario where its just an open venturi (narrowing) pipe facing into the tidal flow .

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