Neat idea.

The engineer in me says, "simplify". So, just build 1/2 a heat pump. If you
pull a vacuum on a properly selected fluid (IPA???) it will boil and cool.
So, all you'd need is a little vacuum pump and a double wall container sized
for a beer can.

I'd further consider a cylinder with "O" rings for seals and read valves.
Just move it back and forth for your power.


There's one concept anyway.

Karl