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Chapter 9
Natural Convection
Chapter 9
NATURAL CONVECTION
Physical Mechanisms of Natural Convection
91C
Natural convection is the mode of heat transfer that occurs between a solid and a fluid which moves
under the influence of natural means. Natural convection differs from forced convection in that fluid
motion in natural convection is caused by natural effects such as buoyancy.
92C
The convection heat transfer coefficient is usually higher in forced convection because of the higher
fluid velocities involved.
93C
The hot boiled egg in a spacecraft will cool faster when the spacecraft is on the ground since there is
no gravity in space, and thus there will be no natural convection currents which is due to the buoyancy
force.
94C
The upward force exerted by a fluid on a body completely or partially immersed in it is called the
buoyancy or “lifting” force.
The buoyancy force is proportional to the density of the medium. Therefore,
the buoyancy force is the largest in mercury, followed by in water, air, and the evacuated chamber. Note
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Buoyancy, Convection, Mass, Heat

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