In energy technology, closed systems are often used in which a heat carrier absorbs heat at one point and releases it at another. In solar technology, for example, solar heat is transferred to the heat carrier (water treated to avoid freezing) in the absorber and is then released to a hot-water boiler via a coil. Absorber and coil are heat exchangers (as are, for example, radiators).
Heat exchangers are a prerequisite for waste-heat utilisation or heat recovery from waste gases, exhaust air and effluent - an important form of energy saving in heating engineering and a multitude of industrial processes (such as the Bayer process for alumina production), as well as for cooling.
A heat exchanger is basically constructed in such a way that the medium that absorbs or releases the heat is separated from the heat carrier by a partition. Heat transfer is by thermal conduction through the partition. The material of the partition therefore has to be a good conductor of heat, but also corrosion resistant and economical. As aluminium fulfils these requirements, it is used for manufacturing all kinds of heat exchangers in the form of strip, for soldering prepared sheet and of special profiles (such as finned tubes), for example in car radiators, in air conditioning technology and solar technology.
When using foil it is possible to construct very compact heat exchangers. This is particularly beneficial in mobile applications such as aircraft, cars or trucks. More importantly, the low weight saves fuel.