vansig wrote: i’m not worried about capturing the xrays; what’s a worry is, how do you contain the hot fluid? what is your container made from? how do you cold-start it?
what is the engine’s principle of operation? how close to ideal does it’s efficiency get?

Use tungsten as the container, which has extremely high boiling points and high tensile strength. Cool the tin by immersing the tungsten, molded as a coil, in water.The vapor will move helices. Cold start the system it using tungsten as a resistor until it melts tin, and so, turn on the machine. For efficiency, I have no idea, but the differences of temperature are huge. The only element better than tin is gallium, but it is very rare.