05-10-2010, 12:57 PM
prepared by:
Sanjay Bharat Dolare
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Introduction
A device designed to transfer heat between two physically separated fluids; generally consists of a cylindrical shell with longitudinal tubes; one fluid flows on the inside, the other on the outside.
Any of several devices that transfer heat from a hot to a cold fluid. In many engineering applications, one fluid needs to be heated and another cooled, a requirement economically accomplished by a heat exchanger. In double-pipe exchangers, one fluid flows inside the inner pipe, and the other in the annular space between the two pipes. In shell-and-tube exchangers, many tubes are mounted inside a shell; one fluid flows in the tubes and the other flows in the shell, outside the all heat tubes. Special-purpose devices such as boilers, evaporators, superheaters, condensers, and coolers are exchangers. Heat exchangers are used extensively in fossil-fuel and nuclear power plants, gas turbines, heating and air conditioning, refrigeration, and the chemical industry. See also cooling system.
A device used to transfer heat from a fluid flowing on one side of a barrier to another fluid (or fluids) flowing on the other side of the barrier.
When used to accomplish simultaneous heat transfer and mass transfer, heat exchangers become special equipment types, often known by other names. When fired directly by a combustion process, they become furnaces, boilers, heaters, tube-still heaters, and engines. If there is a change in phase in one of the flowing fluids—condensation of steam to water, for example—the equipment may be called a chiller, evaporator, sublimator, distillation-columnreboiler, still, condenser, or cooler-condenser.
Heat exchangers may be so designed that chemical reactions or energy-generation processes can be carried out within them. The exchanger then becomes an integral part of the reaction system and may be known, for example, as a nuclear reactor, catalytic reactor, or polymerize.
Heat exchangers are normally used only for the transfer and useful elimination or recovery of heat without an accompanying phase change. The fluids on either side of the barrier are usually liquids, but they may also be gases such as steam, air, or hydrocarbon vapors; or they may be liquid metals such as sodium or mercury. Fused salts are also used as heat-exchanger fluids in some applications.
Most often the barrier between the fluids is a metal wall such as that of a tube or pipe. However, it can be fabricated from flat metal plate or from graphite, plastic, or other corrosion-resistant materials of construction.
A device used to exchange heat from one medium to another often through metal walls, usually to extract heat from a medium flowing between two surfaces. A heat exchanger is usually in the form of a radiator with one fluid flowing inside tubes and the other outside them. Various forms of heat exchangers are air-to-air, air-to-liquid, and liquid-to-liquid.
A heat exchanger is a device built for efficientheat transfer from one medium to another. The medium may be separated by a solid wall, so that they never mix, or they may be in direct contact.[1] They are widely used inspace heating, refrigeration, air conditioning,power plants, chemical plants, petrochemical plants, petroleum refineries, and natural gas processing. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator (i.e. the heat transfer medium).
