Heat Exchangers transfer heat between two or more fluids. Cooling and heating processes use heat exchangers. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and wastewater treatment.
A classic example of a heat exchanger can be found in an internal combustion engine where circulating coolant flows through radiator coils and air circulates past them, cooling the coolant and heating the incoming air. A heat sink, for example, is a passive heat exchanger that transfers heat from an electronic or mechanical device into a fluid medium, such as air or a liquid coolant. Another common use of heat exchangers is to preheat a cold fluid entering a heated process system with heat from the hot fluid exiting the system. In this way, the energy input required to heat the incoming fluid to its working temperature is reduced.
Specific applications for heat exchangers include: – Using the heat from a hotter fluid to heat a cooler fluid – Transferring heat from a hot fluid to a cooler fluid – Utilising heat from a hotter fluid to boil a liquid – Boiling of a liquid while condensing a hotter gaseous fluid – Using a cooler fluid to condense a gaseous fluid In heat exchangers, fluids flow rapidly in order to facilitate the transfer of heat through forced convection. These rapid flows result in pressure losses in the fluids. Heat exchanger efficiency is determined by how efficiently they transfer heat relative to how much pressure they lose. With modern heat exchangers, pressure loss is minimised while heat transfer is maximised and other design goals are met, like withstanding high fluid pressures, resisting fouling and corrosion, and allowing cleaning and repair.