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[[Image:Picture008-2b.jpg|thumb|255px|A water pipe percolator.]]

A '''water pipe percolator''' is a small additional sub chamber within the main chamber of a [[bong|water pipe]] that  
provides in-line smoke-water interaction via [[heat exchanger|heat exchange]] and [[solvation|dissolution]].

==Function and Purpose==

A percolator works by utilizing a pressure differential between its bottom and top in/outlets. Reduced pressure at  
the outlet end is usually provided by the users lungs. The [[fluid]] at the inlet (ie: a smoke, vapor, and air mixture)  
is directed to the bottom of a column of water, where the pressure differential causes the inlet fluid to pass  
though the water in small pockets ([[liquid bubble]]s), and then rise to the outlet.

[[Image:Percolator col 2.gif]]

'''Figure''': Schematic of the flow through a percolator (inlet at bottom, outlet at top).

1. Initial state<br/>
2. Water displacement<br/> 
3. Flow 

*The percolator serves the primary function of cooling the smoke and combustion vapors that pass through it. The surface of the bubbles come into direct contact with the water, where the temperature difference causes an [[heat exchanger|exchange of heat]] between the hot smoke/vapor, and the cool water. Many percolator designs incorporate a number of small openings within the water instead of large singular ones in order to diffuse the smoke into a larger number of smaller bubbles. This serves the purpose of increasing the surface area of the smoke that is in contact with the water and increasing the efficiency of [[heat transfer]].

*A secondary function of the percolator is to trap certain components contained within the smoke. Water soluble substances enter into solution as the smoke/vapor contacts the water, while less soluble substances pass through with relative ease. However, studies conducted by [[Multidisciplinary Association for Psychedelic Studies|MAPS]] and CA-[[National Organization for the Reform of Marijuana Laws (United States)|NORML]] have demonstrated that filtration by solvation is inneffective when consuming smoked cannabis.<ref>Newsletter of the Multidisciplinary Association for Psychedelic Studies - Volume 6 Number 3, Summer 1996 - http://www.maps.org/news-letters/v06n3/06359mj1.html</ref> The studies infer that the solubility of Cannabinoids, the active components in the smoke, are similar to or greater than that of tar, and so no (or negative) "filtration" takes place. There is no data available for tobacco or other substances.

*A tertiary function of the percolator is to hydrate the air-smoke-vapor mixture. Humidity of the air passing through the percolator water is increased. The increased humidity reduces the irritation to the upper respiratory tract experienced by some users according to anecdotal claims.

==Types==

There are a number of percolator designs on the market today. The two most prevalent are the branched and  
cylindrical designs.

 

[[Image:Picture008-2b.jpg|thumb|150px|A Branched Percolator.]]
===Branched===
Branched percolators utilize between 1 and 4 individual flow paths for the smoke to enter the water. This design is more recent than the cylindrical design. Branched percolators are sometimes referred to as "tree" percolators due to their geometry. See image.

[[Image:Percloseupc.jpg|thumb|125px|A Cylindrical Percolator.]]
===Cylindrical===
Cylindrical percolators instead use a single encirculating cylindrical piece to direct smoke to the bottom of the water column. Cylindrical percolators may be essentially interpreted as the branch design with an infinite number of branches compounded together to form one singular flow path. Cylindrical percolators are sometimes referred to as "dome" percolators due to their geometry. See image.

==References==
<references/>
[[Category:Pipe smoking]]
[[Category:Fluid mechanics]]