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Convection cell
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{{Short description|Cyclic flow of convection currents in a fluid}} {{Lead rewrite|date=October 2023}} [[Image:Altocumulus15.jpg|thumb|Altocumulus cloud as seen from the Space Shuttle. Altocumulus clouds are formed by convective activity.]] [[File:Rayleigh–Bénard convection pattern in honey wine with cinnamon floating on top after 10 days of fermentation.jpg|thumb|6-gallon bucket of [[Mead|honey wine]] after fermenting 10 days with cinnamon floating on top. Convection is caused by yeast releasing CO2.]] In [[fluid dynamics]], a '''convection cell''' is the phenomenon that occurs when [[density]] differences exist within a body of [[liquid]] or [[gas]]. These density differences result in rising and/or falling [[convection current]]s, which are the key characteristics of a convection cell. When a volume of fluid is heated, it expands and becomes less dense and thus more buoyant than the surrounding fluid. The colder, denser part of the fluid descends to settle below the warmer, less-dense fluid, and this causes the warmer fluid to rise. Such movement is called [[convection]], and the moving body of liquid is referred to as a ''convection cell''. This particular type of convection, where a horizontal layer of fluid is heated from below, is known as [[Rayleigh–Bénard convection]]. Convection usually requires a gravitational field, but in microgravity experiments, thermal convection has been observed without gravitational effects.<ref>[https://archive.today/20120527090640/http://www.springerlink.com/content/nx7l8r7675471427/ Yu. A.Gaponenko and V. E. Zakhvataev,''Nonboussinesq Thermal Convection in Microgravity under Nonuniform Heating'']</ref> Fluids are generalized as materials that exhibit the property of [[Fluid dynamics|flow]]; however, this behavior is not unique to liquids. Fluid properties can also be observed in gases and even in particulate solids (such as sand, gravel, and larger objects during [[rock slide]]s). A convection cell is most notable in the formation of clouds with its release and transportation of energy. As air moves along the ground it absorbs heat, loses density and moves up into the atmosphere. When it is forced into the atmosphere, which has a lower air pressure, it cannot contain as much fluid as at a lower altitude, so it releases its moist air, producing rain. In this process the warm air is cooled; it gains density and falls towards the earth and the cell repeats the cycle. Convection cells can form in any fluid, including the [[Earth's atmosphere]] (where they are called [[Hadley cell]]s), boiling water, soup (where the cells can be identified by the particles they transport, such as grains of rice), the ocean, or the surface of the [[Sun]]. The size of convection cells is largely determined by the fluid's properties. Convection cells can even occur when the heating of a fluid is uniform.
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