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Creating electricity through pressure difference

  1. Oct 10, 2012 #1
    Now i am a refregration apprentice so by know means am i qualified or mabe have no idea what i am talking.

    now i belief that by heating a gas you increase the pressure it is putting on the object contianing it and by cooling it you reduce that pressure. So is it possible to cool the gas at the top of a tower and heat it at the bottom with a turbine being turned by the rise in pressure.

    also if you where to then put another turbine on the other side where the liquid falls (a one way valve would need to be fitter) would you then concivable generate more electricity then that required to operate a secoundary refrigerant being powered by a compressor??
     
  2. jcsd
  3. Oct 10, 2012 #2

    Ok, generally speaking as temperature increases things expand (become less dense) and hence in the case of air will rise above colder, denser air. So that's good. I'm not too sure what you mean when you say "the side where the liquid falls" but I can tell you that any physics/engineering problem in which you basically say 'can I add x energy to a system and get x+y energy back' the answer is no.

    From what I gather you want to apply heat to a fluid, it will expand, rise, turn a turbine?
    Not a dissimilar idea to a nuclear power station. Converting a small amount of mass into thermal energy, this heats water, water expands, evaporates, turns a turbine. However the energy you get from he system (assuming no losses in the system) will only ever be equivalent to the mass (energy) put into the system. Its the same here if you skip the nuclear bit and just apply heat to a fluid that fluid will not have any more energy to give than the energy you gave it.

    Firstly you have to heat the fluid = energy, it then requires energy to move the turbine and the amount the turbine moves will be proportional to the fluid flow which will depend on the amount of heat applied (energy input) and our good old friend the 2nd law of thermodynamics tells us that if you apply a certain amount of energy to a system this is the total energy available, there is no free buy one get one free energy deal.

    Let me know if I've missed your point but remember that the 2nd law will say NO to any 'free energy' ideas you might have.
     
  4. Oct 10, 2012 #3
    Just to add to that - We do convert pressure changes into electricity all the time. Sound is just a pressure fluctuation and we covert that into electricity with an electro-mechanical transducer, called a microphone. However conversion efficiency is typically about 1%, hence the need for an amplifier that you generally plug into the mains.
     
  5. Oct 11, 2012 #4
    ok thanks for clearing that up

    so when you turn the turbine it takes what type of energy from the heated vapour?


    also when a liquid falls is gravity not effecting it incressing the energy it has (kinetic)??

    the idea i had was not buy one get one free so to speak i know that is impossible. It was about building a device that transported mass higher though heat application and then reharvesting the heat at the top to reheat the liquid at the bottom. Gravity then adds energy that can be harvested as the mass falls.
     
    Last edited: Oct 11, 2012
  6. Oct 11, 2012 #5
    Yeah you are right in the fact that as an object is lifted it's gravitational potential energy is increased, when released this potential energy will be converted into kinetic energy as it falls. However in the case of air in a pipe the gas is not falling because of gravity (air molecules fly around all over the place - have a look at Brownian motion) they fall because the less dense air effectively pushes it down so you have air moving up and air moving down (See convection) hence if you have some kind of turbine in the middle, it will be useless as flow will be equal in both directions.

    Also hot molecules will not retain their heat, they will equilibrate. If you applied heat the the base of a pan of water, the hot water would rise but you would not expect after a few minutes/seconds, for the top water to be substantially hotter than the water at the bottom (unless the pan is so large that light cannot sufficiently reach the base of the pan). Plus by virtue of being hot and having more energy gas molecules will vibrate more, i.e. some of the heat energy will be dissipated by the motion of the molecule.

    Plus im not sure how you would harness the heat energy from a top layer of fluid, its a constant process, by the time the 'hot' fluid has reached the top of the tube its on its way back down again because its not hot any more (relatively speaking).
     
  7. Oct 13, 2012 #6
    ok

    how i would harness the heat from the top would be to put a refregeration cycle in it with the evaporation coil at the top and a condensing coil at the bottom. this would then move the heat to the bottom while allowing the heated vapour to travel upwards. The greatest problem with this idea would be as you said preventing the heat from balancing out.

    your example of the pan is not bang on the idea i have its more i heat the water into steam then letting that steam travel upwards (turing a turbine, denser vapour forceing it upwards?) then once it reaches the top of a insulated tower turning that steam back into water and letting it fall (turing another turbine, less dense vapur forcing it down??)

    now by cooling the water you would be creating a low pressure zone inside the tower/pipe as well as a high pressure zone. if we could keep a low pressure zone on the side that the water falls would it be effected by gravity then or would it still be forced down but the less dense particales of air.

    if this upload works you will see the idea im talking about
     

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