How heat exchangers work

Written by john albers
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A heat exchanger is a device used to passively transfer heat from one material to another. These materials may be liquid or gaseous, depending on the situation in which the heat exchanger is being used. There are many models and types of heat exchangers, but they essentially work based on the laws of thermodynamics. One of those laws states that when an object is heated, the heat energy contained within that object will diffuse outward to the surrounding environment, until the heat energy in the object and in the environment have reached equilibrium.

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How Does a Heat Exchanger Work?

Heat exchangers are basically two chambers separated by a single wall. This may take the form of a reservoir, but to be more effective, the maximum amount of the two chamber’s volumes must be in contact with each other. As a result, most heat exchangers are simply two passageways of pipe that snake back and forth, turning in on themselves.

A heated material is passed through one pipe. This material needs to be cooled in a hurry, but it would not be economical to chill the material by refrigeration or chemical means. The other pipe is filled with another material, which is cooled, typically at or near room temperature. As a result of the two materials being in close contact with each other, the heat diffuses between the two until they reach an equal temperature.

Where Are Heat Exchangers Used?

Heat exchangers are used in all sorts of industrial processes. The size and type of heat exchanger for each process can be customised, as they all follow similar principles. Instead of using unnecessary coolant, many industries instead pipe in a fluid or chemical that needs to be heated anyway, saving heat energy that would otherwise be wasted.

Absorption refrigerators use heat exchangers to condense the chemicals within their closed systems from a vapour to a liquid. Waste water treatment plants run heated materials alongside waste water pipes containing anaerobic digesters, which must be kept at very warm temperatures to do their jobs in breaking down waste.

The human lungs are also a good example of a heat exchanger. They are very open with lots of surface volume. Cool air comes in and presses up against the tissue, behind which is hot blood. The heat from the blood transfers to the air, helping to cool the body.

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