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

  • Thread starter qazwsxedc
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  • #1
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Main Question or Discussion Point

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?)
 

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  • #2
russ_watters
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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.
 
  • #3
1,838
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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.
 
  • #4
1,041
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When you price fuels, you have to do it on a $/(delivered kJ) basis. Nitrogen looks very expensive on that basis.
 
  • #5
1,838
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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.
 
  • #6
4,662
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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.
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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