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What Is a Coalescer?

A mechanical coalescer draws water molecules out of a mixture.
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  • Written By: Christian Petersen
  • Edited By: Susan Barwick
  • Last Modified Date: 15 September 2014
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    Conjecture Corporation
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A coalescer is a device that is used to separate and consolidate the distinct components of a mixture — usually a liquid emulsion. This process known as coalescence. Devices of this type have many uses but are primarily used on an industrial scale in the petroleum and refining industries to separate and remove moisture from fuel mixtures. A mechanical coalescer uses a series of filters or dividers, known as baffles, to induce water molecules to move from a mixture and to collect together. An electrostatic coalescer uses weak electric charges to attract molecules of water to the surface where they undergo collection.

The petroleum and refining industries make extensive use of coalescers to remove all traces of water or other contaminants from various products from raw crude to high grade aviation fuels. Many ground vehicle and aircraft fuel delivery systems incorporate one or more coalescer devices to remove any moisture that may be present in the fuel due to condensation, contact with moist air, or other factors. Most coalescer devices are small, removable cartridges with no moving parts of their own, but larger coalescers may be used in industrial applications.

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Coalescers work by attracting miniscule droplets of water or other liquid, possibly even as small as a single molecule. As the droplets collect, they are gathered together by the force of molecular attraction and surface tension. When they reach a sufficient size, they can be removed from the system by gravity or by centritpetal forces generated by spinning the coalescer assembly. The material to be separated by a coalescer may be in liquid or vapor form depending on the component substances.

A mechanical coalescer relies on a series of barriers, known as baffles or filters, made of very fine mesh, which can be made from a variety of materials, including fiberglass fibers. The vapor or liquid passes through the filter, and the water is attracted to the filter material or the surface of the baffles. In an electrostatic coalescer, a weak electric charge is passed through a collection device which imparts a tiny charge that attracts molecules of water or other material designated for removal.

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