Answer: transfer heat from one fluid to another without having to mix them.
A heat exchanger is a device that transfers heat from one fluid (most often air or water) to another fluid, without having to mix them. The heat exchange takes place through two conduits which are brought into contact with one another. The direction of flow of fluids can be in the same direction or in opposite directions. Depending on the configuration of the installation, a heat exchanger can both heat and cool the fluid which will be used later. A heat exchanger therefore allows energy savings, sometimes substantial. The most popular heat exchangers for the general public are heat pumps, often associated with ventilation systems in buildings, such as VMCs. You too, send us your brico question