Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics. The radiator is always a source of heat to its environment, although this may be for either the purpose of heating this environment, or for cooling the fluid or coolant supplied to it, as for engine cooling. Despite the name, most radiators transfer the bulk of their heat via convection instead of thermal radiation. Spacecraft radiators necessarily must use radiation only to reject heat.
The Roman hypocaust, is an early example of a type of radiator for building space heating. The heating radiator was invented by Franz San Galli, a Prussian-born Russian businessman living in St. Petersburg, between 1855 and 1857.
