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Air Flow in a 10m. pipe - generating electricity ?

  1. May 5, 2012 #1
    I have this idea about creating a 10 meter plastic/metal pipe that would go from a house roof to the ground and having a "U' shape close to the ground so that both holes are directed at the sky.

    Does anyone have a clue if the difference in atmospheirc pressure between both holes (10 meters difference in heigth) would generate enough of an air flow (in the pipe of course) to make a little dynamo (shafted in the hole close to the ground) generate electricity ?

    Regards,
    Jonathan
     
  2. jcsd
  3. May 5, 2012 #2

    russ_watters

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    Staff: Mentor

    Please ask yourself this: if putting in a pipe would make air flow, why would the air not flow even without the pipe? A pipe is just a restriction to flow.
     
  4. May 5, 2012 #3
    Russ Waters is correct. The open air has no restrictions on its ability to flow other than air pressure. Therefore there would be much more airflow between the two locations without putting a pipe in place than would actually flow through the pipe. So you could generate more energy by putting up an equal number of equally sized dynamos in the open air than you would generate in the pipe.
     
  5. May 6, 2012 #4

    AlephZero

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    Posts #2 and #3 are right, but this could work not because of pressure difference, but temperature difference. A 10 meter tall pipe would probably be too short, but if you had a pipe the height of a skyscraper, there would be a flow of warmer air from ground level up the pipe. This needs something to get the flow started (otherwise Russ's objection still holds), but solar radiation will heat up the solid pipe faster than the surrounding air during the day, and that is enough to start the air flow. If the pipe cools down faster than the air at night, the flow direction might be reversed.

    I don't think anybody has used this to generate "useful" amounts of electricity, generation, but it is used for energy efficient ventilation in tall buildings.
     
  6. May 6, 2012 #5

    mfb

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    There are experimental power plants using this concept.
     
  7. May 7, 2012 #6
    thank you very much for your precise explanations . Very helpful.
     
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