Temperature exchange between a gas and a liquid In the case of air-water heat exchangers (also called gas-water heat exchangers), there is a temperature exchange between a gas (usually air) and a liquid. Finned heat exchangers can cover various areas of application: - heating and evaporating, - cooling and condensing as well as heat recovery. In this context, lamellar heat exchangers are also called air heaters or air coolers. Air-water heat exchangers are often also used as exhaust gas heat exchangers or flue gas heat exchangers in order to recover the energy from warm or hot exhaust gases. Lamella packs for a large exchange area In order to achieve the largest possible exchange surface between the air and the medium (liquid) within the heat exchanger, lamellas or lamella packs are attached to the pipe system.