heatexchange

A heat exchanger is a device that transfers thermal energy between two or more fluids or media at different temperatures while preventing mixing. Heat transfer occurs through a solid wall separating the streams and is driven by temperature differences. The rate depends on the temperature driving force, the heat transfer area, and the thermal resistances of the wall and boundary layers. In many cases, the outlet temperatures are limited by the streams' heat capacity rates.

Common configurations include shell-and-tube exchangers, plate exchangers, double-pipe exchangers, and air-cooled or finned-tube designs. Shell-and-tube units are robust for high pressures and temperatures; plate exchangers offer high heat transfer in compact footprints; double-pipe units are simple and inexpensive.

Performance is characterized by the heat transfer rate Q, equal to U A ΔT_lm, or by NTU and effectiveness in more detailed design. Practical design must account for fouling, pressure drop, material compatibility, corrosion, and ease of cleaning.

Applications include power generation, HVAC, chemical processing, refrigeration, petrochemicals, and electronics cooling. Design standards and codes, such as ASME for pressure vessels and PED in the EU, govern safety testing and compliance for heat exchangers.