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Lecture 23 Natural Convection PPT

Lecture 23 Natural Convection PPT - 1 MECE 4364 Heat...

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MECE 4364 Heat Transfer Prof. Dong Liu Department of Mechanical Engineering University of Houston 1 Lecture 23 – Nov 09, 2010 Lecture 23 Free (Natural) Convection 2
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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 3 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 4
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