Making stuff cool and keeping it that way has been a pretty essential part of human civilization for thousands of years, with only in the past few hundred years man-made methods having become available that remove the reliance on the whims of nature and lugging around massive blocks of ice. The most important cooling method is undoubtedly that of vapor-compression refrigeration, but this is hardly the only method to transfer thermal energy from one location to another.
For example, we recently covered an elastocaloric cooling project by a group of scientists that uses strips of NiTi metal. By flexing these they induce a cooling effect which when put in a number of stages serves to transfer a significant amount of thermal energy between both sides, much like a vapor-compression system but without the gases and compressor. Meanwhile the Seebeck effect is relatively well-known from Peltier thermocouple devices, and features heavily in portable refrigerators and kin where these solid-state devices can also transfer thermal energy.
Of course, along with how they function the major question with all of these cooling technologies is how efficient they are, as this determines when you’d want to even consider them for a specific application.
