Energy conversion

ummm, a steam engine?

 

Heat by itself can't be converted, as it is the highest entropy (most disordered) form of energy. If you have a temperature difference however - something that is hot, and something else that is cold, then there are whole families of heat engines that will produce useful forms of energy, while cooling down the hot thing and warming up the cold thing. A Stirling (hot air) engine is able to produce useful work when the temperature difference is only a few degrees.