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| {{Incomplete|date=May 2009}}
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| [[Image:Schneekanone.jpg|thumb|Forced convection by a fan in a snow machine.]]
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| '''Forced convection''' is a mechanism, or type of transport in which fluid motion is generated by an external source (like a pump, fan, suction device, etc.). It should be considered as one of the main methods of useful heat transfer as significant amounts of heat energy can be transported very efficiently.
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| ==Applications==
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| This mechanism is found very commonly in everyday life, including [[central heating]], [[air conditioning]], [[steam turbines]] and in many other machines. Forced convection is often encountered by engineers designing or analyzing [[heat exchanger]]s, pipe flow, and flow over a plate at a different temperature than the stream (the case of a shuttle wing during re-entry, for example).
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| ==Mixed convection==
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| In any forced convection situation, some amount of natural convection is always present whenever there are [[g-forces]] present (i.e., unless the system is in free fall). When the natural convection is not negligible, such flows are typically referred to as [[mixed convection]].
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| ==Mathematical analysis==
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| When analyzing potentially mixed convection, a parameter called the [[Archimedes number]] (Ar) parametrizes the relative strength of free and forced convection. The Archimedes number is the ratio of [[Grashof number]] and the square of [[Reynolds number]], which represents the ratio of buoyancy force and inertia force, and which stands in for the contribution of natural convection. When Ar >> 1, natural convection dominates and when Ar << 1, forced convection dominates.
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| :<math> Ar= \frac{Gr}{Re^2} </math> <ref>{{cite book | author=[[Frank P. Incropera|Incropera, F. P.]]| title=Fundamentals of Heat and Mass Transfer, 5th Ed.| publisher=Wiley| year=2001 | id=ISBN 978-0471386506 }}</ref>
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| When natural convection isn't a significant factor, mathematical analysis with forced convection theories typically yields accurate results. The parameter of importance in forced convection is the [[Peclet number]], which is the ratio of advection (movement by currents) and diffusion (movement from high to low concentrations) of heat.
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| :<math> Pe=\frac{U L}{\alpha }</math> | |
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| When the Peclet number is much greater than [[1 (number)|unity]] (1), advection dominates diffusion. Similarly, much smaller ratios indicate a higher rate of diffusion relative to advection.
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| ==See also==
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| * [[Combined forced and natural convection]]
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| == References ==
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| <references />
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| ==Bibliography==
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| * {{cite book | author=Cebeci, Tuncer | title=Convective Heat Transfer | publisher=Springer | year=2002 | id=ISBN 096684615X}}
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| * {{cite book | author=Burmeister, Louis | title=Convective Heat Transfer, 2E | publisher=Wiley-Interscience | year=1993 | id=ISBN 047157709X}}
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| * {{cite book | author=Hewitt, G.F| title=Process Heat Transfer | publisher=CRC Press Inc| year=1994 | id=ISBN 0-8493-9918-1}}
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| [[Category:Fluid dynamics]]
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| [[Category:Heat transfer]]
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| [[Category:Convection]]
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| [[zh:对流传热]]
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