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Would it be possible to create a sterling engine out of liquid nitrogen and air?

  1. May 10, 2009 #1
    Is the heat difference enough to cause a noticeable power output in some type of sterling engine? Liquid nitrogen is quite cheap (alternative fuel source?)
     
  2. jcsd
  3. May 10, 2009 #2

    russ_watters

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    Staff: Mentor

    Setting aside for now the practical difficulties in sterling engines (they are efficient, but produce a low power density) and in using liquid nitrogen:

    The heat of vaporization of nitrogen is 202 kJ/kg
    The heat of combustion of gasoline is 47,000 kJ/kg

    You'd need more than 200 times as much vaporized liquid nitrogen as burned gasoline to ge the same amount of energy output.
     
  4. May 10, 2009 #3
    Hmmm, the vaporation heat will just be the waste heat you have to dump. The amount of useful work will be about a factor 3 larger.
     
  5. May 10, 2009 #4
    When you price fuels, you have to do it on a $/(delivered kJ) basis. Nitrogen looks very expensive on that basis.
     
  6. May 10, 2009 #5
    Perhaps you could get radioactive waste free of charge and use that to power an engine. I think that caesium 137 will yield 1 Watt per gram. The half life in 30 years, so you can imagine a car being powered by a block of ceasium that would only have to be replaced every ten years or so.
     
  7. May 11, 2009 #6
    Where would I get a 1 kilowatt (about 1 HP) Cesium source? Assuming about 1 MeV per decay, this corresponds to about 6.26 x 1015 decays per second, or 169,000 Curies. I once measured the shielding elffect of lead around a 1 milliCurie cesium source, and decided that 2 inches of lead would attenuate the radiation by about a factor of 10. So how many tons of lead are required to shield this source?
    Note: spelling: Stirling engine.
     
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