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'''Natural convection''' is a mechanism, or type of [[heat transport]], in which the fluid motion is not generated by any external source (like a pump, fan, suction device, etc.) but only by density differences in the fluid occurring due to [[temperature gradient]]s. In natural convection, fluid surrounding a heat source receives heat and by [[thermal expansion]] becomes less dense and rises. The surrounding, cooler fluid then moves to replace it. This cooler fluid is then heated and the process continues, forming a convection current; this process transfers heat energy from the bottom of the convection cell to top. The driving force for natural convection is buoyancy, a result of differences in fluid density. Because of this, the presence of a [[proper acceleration]] such as arises from resistance to gravity, or an [[equivalence principle|equivalent]] force (arising from [[acceleration]], [[centrifugal force]] or [[Coriolis effect]]), is essential for natural convection. For example, natural convection essentially does not operate in free-fall ([[inertial]]) environments, such as that of the orbiting International Space Station, where other heat transfer mechanisms are required to prevent electronic components from overheating.
Natural convection has attracted a great deal of attention from researchers because of its presence both in nature and engineering applications. In nature, convection cells formed from air raising above sunlight-warmed land or water are a major feature of all weather systems. Convection is also seen in the rising plume of hot air from [[fire]], [[plate tectonics]], oceanic currents ([[thermohaline circulation]]) and sea-wind formation (where upward convection is also modified by [[Coriolis force]]s). In engineering applications, convection is commonly visualized in the formation of microstructures during the cooling of molten metals, and fluid flows around shrouded heat-dissipation fins, and solar ponds. A very common industrial application of natural convection is free air cooling without the aid of fans: this can happen on small scales (computer chips) to large scale process equipment.
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