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Extracting energy from air at room temperature help

  1. Jun 27, 2007 #1
    I have questions(at the end) regarding an idea I thought of before..

    Using the Kinetic Molecular Theory of Gases (KMT), we have air molecules all moving in random directions at high mean speed with it's heat content as the mean of it's kinetic energy at room temperature. The movement never stops, maybe except in absolute zero temperature..

    -First and foremost, I'd like to make it clear that I'd like to extract this kinetic energy into something that could achieve work..

    -Let's say we have a 'lucky tube'(this is purely an example..:biggrin:) For some extreme luck, everytime the air molecules collided with the tube's inner walls, it hits the right spot(a crack, a dirt, a scratch, etc..) in a way so it always get deflected to the rear end of the tube.

    -In such process, what used to be random motion molecules of air molecules are achieving order, they begin to move from one end to the other an orderly fashion, randomness is being transformed to order slowly.

    -In later stages of development, all the the molecules are now moving in one direction along the tube, front to back. In this manner, they still have the same level of kinetic energy right? And the same heat content.

    -Then we decide to place a turbine at the rear end of the tube. The turbine is attached or geared to an axle that drives a wheel of the automobile, thus, achieving work.

    -After the air has passed thru the turbine, which extracted mechanical energy from the air, the air stream will slow down.

    -Since all the air molecules are all moving in one direction(maybe in a twisting fashion after passing the turbine) and have slowed down, Its mean kinetic energy has decreased, therefore the heat content also, and finally, temperature drops.

    Finally, we have an engine that extracts the heat content of the air, does work and exhausts a stream of air that is colder than before.

    Basically, this is an indirect form of solar energy.. Sun heats ground, ground heats air and our engine extracts that heat into mechanical energy. Engine should work as long as air is in gaseous state.

    My questions are:

    -Given, the 'lucky tube' does exist, is it really possible to create unidirectional movement with KMT considering other aerodynamic factors as boundary layer, Reynolds Number, laminar flow, Bernoulli Effect, etc?

    -I know this is silly, but for the sake of argument, will it break Conservation of Energy?(not IMO, but a lot of people I mentioned this can't believe I won't be breaking any law)

    -Is the idea totally impossible to recreate? Are there other ways?
  2. jcsd
  3. Jun 27, 2007 #2


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    Ever heard of Maxwell's Demon? You may want to research that term.
  4. Jun 27, 2007 #3
    Yep, I did during my research on KMT, I also stumbled upon the 'Hilsch vortex tube' device(industry spot air cooling devices). I even analyzed the device closely.

    BY KMT, it accurately predicts where along the device will the air become cold and becomes hot. But it doesn't predict the air velocities so I assume, some factors need to be considered as well, especially air pressure.

    In my 'lucky tube' it should work with ambient atmospheric pressure.
  5. Jun 27, 2007 #4


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    You could look into the "Brownian Ratchet".
  6. Jun 27, 2007 #5
    Gee, thanks! So now, it breaks the 2nd law of thermodynamics?


    There was argument that it won't work due to the ratchet being affected by the same forces that affected the gear, hence would slip.

    But what if allow counter clockwise, and clockwise rotation, because we will attach it to a microscopic electric generator, hence will generate alternating electric current. AC electricity can produce work, right?

    It won't be called the 'ratchet' anymore, I also doubt the ratchet but it doesn't need to end there.

    I also predicted it won't produce any heat gradient but cooling will be observed, so it will violate 2nd law of thermodynamics.

    But I still wouldn't say it as perpetual motion, if you put such device in a perfectly insulated container, the temperature will drop down until the gas solidifies, by then, the motor will stop working..

    Such motor for making energy will not be useful in deep space exploration, it'll freeze the whole ship, but maybe in untried applications, it might make a very efficient thermo-electric generator.

    I wish someone would argue, the violation of 2nd law made me think twice about it.
    Last edited: Jun 28, 2007
  7. Jun 28, 2007 #6
    Your idea violates the laws of thermodynamics. (It's fairly trivial to show that if such a device worked, you could use it to continuously create free energy; e.g. cool gas with "lucky tube" / "Brownian ratchet", use power to run computer or turn engine against friction, let gas recapture heat from used power, cycle restarts.) As such, this thread isn't "speculative", it's "science fiction".
    Last edited: Jun 28, 2007
  8. Jun 28, 2007 #7
    I'm sorry, but you're not getting it, it cannot create free energy, it cannot run forever.

    Yes, it does break 2nd law of thermodynamics, but it doesn't break Conservation of energy.

    It cannot scavenge it's own power, like what you said for example, get energy from the heat of computer, cooling and powering it.. It doesn't work that way, any losses(computers are inefficient at generating heat) will make it NOT self-sustaining.

    For any close or isolated systems, theoretically, it can only be as efficient as the heat generating device. It cannot work as free energy/overunity device.

    If work will not be extracted from it, like turbine that is not powering anything, no reduction in temperature will result.
    Last edited: Jun 28, 2007
  9. Jun 28, 2007 #8


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