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A Sterling Engine is a closed system. The "hot" side oscillates between higher temperature with higher pressure and lower temperature with lower pressure. Does Nature switch back and forth between one temperature/pressure combination and another temperature/pressure combination without loss of energy within the closed system?

The International Sterling Engine Society says they can get 60 Watts from a 50 degree temperature differential. Is there the equivalent of 60 Watts of power pulled from the hot tank? If not, where does the 60 Watts come from?

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    $\begingroup$ A 'closed system' in physics has a very specific meaning, which is not satisfied simply by sealing the working fluid into the engine. $\endgroup$
    – user2963
    Commented Feb 29, 2012 at 2:24
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    $\begingroup$ And yes, heat does transfer from hot to cold. $\endgroup$
    – user2963
    Commented Feb 29, 2012 at 2:24

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A Stirling engine moves a fluid from a hot end to a cold end - extracting mechanical work as it does so. The power input comes from maintaining the temperature of the hot end - usually by burning some fuel externally.

The 'clever' part of a Stirling engine, and the thing that gives it it's high efficiency, is that the hot end of the mechanism stays hot and the cold part stays cold, so you don't waste energy constantly re-heating a piston

enter image description here

image from http://en.wikipedia.org/wiki/Stirling_engine - It's an alpha type engine, less common in practice but easier to understand

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