There’s a lot of energy in the vaporization phase change. In the form of water changing from a liquid into a gas, it has been at the center of most of the world’s energy production systems for the last century. Recently, direct energy conversion has started replacing it with wind and photoelectric power, and hydro-power always did fine without it(1). Although phase change is unlikely to ever power starships, it still has a future in solar collectors and nuclear reactors, most designs for fusion reactors… and it may very well be the best way to cool a starship.
Gaseous water is so common it has its own name; steam. But all materials have a gas phase(2); it’s just that most of them become gases at temperatures that are outside of our usual experience, and that are far beyond the needs of industrial processes.
The following table lists some interesting materials for spaceship cooling using the vaporization phase change. It also highlights the fact that, in most cases, the vaporization phase change transports much more energy than temperature change in the fluid phase.
Latent Heat of vaporisation
Temperature difference required to equal vaporisation