General definitions
Heat exchangers ? Definitions and general principles

The most general definition of a heat exchanger is that of a device for transferring heat from a source to a sink. The source and sink may consist of a fluid flow (the most common case), or a fluid and a solid (a frequent occurrence in electronic cooling). In either case, the fluid or fluids exchange heat with an exchange wall, which may be the wall separating the fluids or the surface of the solid in contact with the fluid. There are also heat exchangers with direct contact between the fluids.

Two main classes can be distinguished