The thread on solar powered shop got me going on this. Thinking about what materials would be good solar energy converters, I wound up learning that gasoline has one of the highest levels of thermal expansion when heated. It would seem that ethyl alcohol, gasoline, and paraffin all have high expansion characteristics with temperature changes. Paraffin (wax) in particular is a good model because it's used in thermostats and endures countless cycles of heating and cooling without failure or change in operating parameters.
Now I'm wondering how efficiently this process can convert absorbed heat into mechanical motion, and how well the process deals with the high pressures that could result from a closed system containing one of these materials. I wonder for instance how much pressure can be generated by a material before it is caused to deviate from its expansion characteristics as heat is applied. In other words, can you stop it from expanding by containing it within a sealed pressure vessel?
Wax is one thing, as it goes through a phase change between a liquid and a solid, but ethyl alcohol for example, or gasoline, both remain liquids. They could be pumped into a chamber which is then exposed to concentrated sunlight, made to do work as the temperature rises, then flushed into a radiator to cool as replacement liquid is allowed to take its place. The circulation of the fluid could be passive, with the operating of the valves done electronically. The work done by the expansion of the liquid is stored in some way for later use.
Thoughts on this anyone?