Radiators and convectors

Radiators and convectors are types of heat exchangers designed 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.

One might expect the term "radiator" to apply to devices which transfer heat primarily by thermal radiation (see: infrared heating), while a device which relied primarily on natural or forced convection would be called a "convector". In practice, the term "radiator" refers to any of a number of devices in which a liquid circulates through exposed pipes (often with fins or other means of increasing surface area), notwithstanding that such devices tend to transfer heat mainly by convection and might logically be called convectors. The term "convector" refers to a class of devices in which the source of heat is not directly exposed.
n automobiles, with a liquid-cooled internal combustion engine, a radiator is connected to channels running through the engine and cylinder head, through which is pumped a liquid (coolant). This liquid is typically a mixture of water with ethylene glycol (a.k.a. antifreeze) and a little corrosion inhibitor.

Fluid cycle

The fluid is pumped in a closed system from the radiator to the engine, where it absorbs and conducts heat away from the engine parts and carries the heat, primarily, to the radiator. The radiator is, on many conventional vehicles, typically mounted behind the vehicle's grille, with outside air driven through the radiator by the vehicle's forward motion.

There are other mounting options for the radiator, especially in mid- and rear-engined vehicles, and some vehicles have characteristic body ducts and vents to ensure that air is conducted through the radiator core.

Movement of the air through the radiator usually needs to be supplemented by a fan so that the engine can be cooled while stationary or working hard. However the fan will absorb excessive power at speed, so variable pitch, or friction drive, mechanical fans and electric fans are normally used on faster vehicles such as cars. Some vehicles, such as some liquid-cooled motorcycles, do not have any supplementary feature for inducing airflow through the radiator.

The radiator transfers the heat from the fluid inside to the air outside, thereby cooling the engine.