Of further interest for those wishing to understand the rather simple principles involved:
http://en.wikipedia.org/wiki/Stirling_engineBasically, imagine a closed cylinder engine with a rather large volume on top of the cylinder. If you heat the air in that volume, it will expand, pushing the piston down. If you cool the air in that volume, it will contract, pulling the piston back up.
You could do this manually, applying heat to the top, then cold. Naturally, this would cause the piston to move up and down.
But it is much easier to have a loose fitting "extra" piston in that volume which just shuttles the air between a hot portion of the volume and a cold portion of the volume.
Of course, the timing has to be right, so the air gets cooled when the power piston is at the bottom of its stroke, and heated when it is the top of its stroke.
Thus, animated GIFs showing all this going on:
http://en.wikipedia.org/wiki/File:Alpha_Stirling.gifhttp://en.wikipedia.org/wiki/File:Beta_stirling_animation.gifThe one I built that didn't work was of the beta type. One major problem was making good seals with low friction. I should have foreseen that before I designed it, though, so naturally, I had to blame the altitude instead of my poor engineering skills. I later thought of using rollsock seals, but that would have involved mechanical processes beyond my capabilities.
As I mentioned, this will not work at all if there is no air (working medium) in the hot and cold chambers --that is, with a total vacuum. So, projecting from this idea, it will work better and better as the working medium total pressure (density) is greater and greater.
The article also shows Stirling engines being heated by solar dishes, as I touched on previously.
I understand, but cannot document right now, that nuclear heat is used to run Stirling engine generator-sets for satellites and space probes and the like, with helium at 3000 psi instead of air for the working medium.
Something I didn't know is that the more modern developments of the Stirling operating principle were made by Phillips so they could sell more radios! Interesting, eh?
Terry, 230RN