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Thread: Calculating flow rate from air to water

  1. #1

    Calculating flow rate from air to water

    Hi,

    Im currently looking at a symstem where air is pumped down a pipe and up through a bigger pipe which lifts water from above. Just wondering if there is anyway of calculating what the flow rate would be through the water if i know what the air flow rate it.

    Any help would be appreciated.

    Cheers.

  2. #2
    Technical Fellow jboggs's Avatar
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    I've read your question four times and have no idea what you're asking. A diagram would help.
    The air is "lifting" the water? From above? Huh?

  3. #3
    Oops I meant lifting water from below.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by miked_27 View Post
    Hi,

    Im currently looking at a symstem where air is pumped down a pipe and up through a bigger pipe which lifts water from above. Just wondering if there is anyway of calculating what the flow rate would be through the water if i know what the air flow rate it.

    Any help would be appreciated.

    Cheers.
    Flow rate will be derived from differential pressure, size of pipes, etc..

    And, yes there is a way to calculate flow in defined fluid systems - - but you have not provided any usable information on what that system is.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
    Sorry it's a dredging system. Air is pumped down the annulus pipe and flows into the main bore at the bottom and this main bore is filled with water.

  6. #6
    Technical Fellow jboggs's Avatar
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    Upon encountering the water the air forms bubbles and rises to the top surface of the water. How is the air "pushing" the water anywhere? Unless there's enough airflow to overwhelm the water with unmanageable bubble sizes.

    "Just wondering if there is anyway of calculating what the flow rate would be through the water if i know what the air flow rate it." That makes no sense. First you ask us how to calculate the flow rate through the water, then you tell us you know what the air flow rate is. Sorry. Just confused.

  7. #7
    Senior Engineer
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    I just done the calculation using Bernoulli's Equation as shown:
    2" stainless steel pipe diameter = 0.05m
    length of the pipe = 20m
    roughness = 0.002
    relative roughness = 0.04
    friction factor,f = 0.50506
    ΔP = 2 bar
    Δx/D = 400
    By substituting all the value into this formula, i got V= 22m/s
    V=square root of [(2ΔP)/p(4f(Δx/D)−1)] A=pie*r^2 = 0.00196349541 m^2
    Q=VA= 22x0.00196349541= 0.043 m^3/s = 43 l/s

    It seems impossible for the 2" stainless steel pipe with water pressure of 2 bar to have a water flow rate of 43 l/s. So wan to ask where i got wrong ?

    Thank you

  8. #8
    Principle Engineer
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    Search for a thread titled "Simple Airlift Pump Equations?? "

    and see my answer.

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