BF1-Ch02

BF1-Ch02 - Chapter 2 Introduction to Conduction The conduction rate equation Considering one-dimensional heat transfer x x dT q k A dx =" x x x

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Unformatted text preview: Chapter 2 Introduction to Conduction The conduction rate equation Considering one-dimensional heat transfer x x dT q k A dx = - " x x x q dT q k A dx = = - Heat flux is a directional quantity “A” is area normal to the heat flow direction. fig_02_03 Alternative form of the Fourier Law: where is the heat flux in a direction “n” normal to an isothermal surface NOTES: 1. Fourier law: a generalization based on experimental evidence 2. Fourier law defines k, the property thermal conductivity " n n T q k n d = - " n q • For a three-dimensional case, " " " " " ( ) x y z x y z q iq jq kq T T T q ik jk kk x y z = + + = - + + x y z Thermal Conductivity Definition: For most materials, Isotropic materials For an anisotropic material In general, " ( ) x x T x q k d d = - " ( ) y y T y q k d d = - " ( ) z z T z q k d d = - x y z k k k k = = = x y z k k k d solid liquid gas k k k More on thermal conductivity For solids, k = k electronic + k phonon k electronic : large for pure metals k phonon : large for well ordered materials like quartz, diamond etc....
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This note was uploaded on 07/07/2008 for the course MEM 345 taught by Professor Cho during the Spring '07 term at Drexel.

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BF1-Ch02 - Chapter 2 Introduction to Conduction The conduction rate equation Considering one-dimensional heat transfer x x dT q k A dx =" x x x

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