Author: Mohamed Fawzy Elsayed
The evaporator is one of the main components of a refrigeration system, in which refrigerant evaporates for the purpose of extracting heat from the surrounding air, chilled water, or other substances.
In vapor compression refrigeration systems, the evaporator is also an indirect-contact heat exchanger.
Evaporators can be classified into three categories, depending on the medium or substance to be cooled:
An air cooler is an evaporator that cools the air directly in a refrigerated space or piece of equipment (such as a packaged unit). Conditioned air is then distributed through air distribution systems.
In an air cooler, the refrigerant flows inside the metal tubes or finned tubes while air flows over them.
In a liquid cooler, chilled water is cooled to a lower temperature and is pumped to remote air handling units, fan coils, or other terminals for air conditioning or other applications.
An evaporator can be used to produce ice directly, such as an ice maker in an ice harvester of an ice storage system.
A liquid cooler is different from a chiller. A liquid cooler is an evaporator, a component of a refrigeration system, whereas a chiller is a refrigeration package to produce chilled water.
The refrigerant feed for air and liquid coolers and ice makers can be classified mainly into the following three types:
1-Dry-expansion or direct-expansion (DX):
In evaporators with dry- or direct-expansion refrigerant feed, liquid refrigerant is fed through an expansion valve and a distributer, flows inside the tubes in a finned coil, the evaporator, and is completely vaporized and superheated to a certain degree before reaching the exit of the evaporator.
2-Flooded refrigerant feed:
In evaporators with flooded refrigerant feeds, liquid refrigerant is fed through a throttling device and vaporizes outside the tubes within a shell. The refrigerant-side surface area is always wetted by the liquid refrigerant, which results in a higher surface heat-transfer coefficient.
In liquid overfeed evaporators, liquid refrigerant is fed by a mechanical or gas pump and is then overfed to each evaporator. The inner surface in an overfeed evaporator is also wetted by liquid refrigerant.
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About the author: Mohamed Fawzy is a mechanical engineer who has a good experience in air conditioning,fire protection and plumbing systems design. He has B.Sc. Degree in mechanical power engineering From Mansoura University, Year 2005. He is currently working as a design engineer for allied consultant company since 2005 till now.He enjoys helping others succeed and he teaches his strategies in the design
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