MECE 4364 Heat Transfer
Prof. Dong Liu
Department of Mechanical Engineering
University of Houston
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Lecture 23 – Nov 09, 2010
Lecture 23
Free (Natural) Convection
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Lecture 23
Free Convection: Overview
Free Convection (or Natural Convection)
fluid motion
induced by
buoyancy forces
buoyancy forces
arise when there are
density gradients
in a fluid and a body
force proportional to density
Density Gradient
due to temperature gradient
Body Force
gravity (function of mass)
thermally driven flow
Basic Principle
: heavy fluid
falls and light fluid rises
creating
vortices
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Lecture 23
Overview
Internal vs. External
free convection can be generated in a duct or enclosure (internal)
along a free surface (external)
in both internal & external cases, free convection can
interact
with
forced
convection (mixed convection)
Free Boundary Flow
occur in an extensive quiescent fluid (
i.e.
, infinite, motionless fluid)
no forced convection
induces a boundary layer on a
heated or cooled surface (T
s
≠
T
∞
)
can generate plumes and buoyant jets
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