H1 - INTRODUCTION heat transfer accrue in three ways...

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Unformatted text preview: INTRODUCTION heat transfer accrue in three ways conduction ,convection ,and radiation. Heat transfer by conduction is best done in solids where the thermal conductivity is high. Heat transfer by conduction accrue as a result of temperature difference between two bodies in contact with each other. So , heat moves from the higher temperature to the lower temperature object. It result from molecular interaction between adjacent molecule. Also, there another mechanism which is caused by free electron which accrue in free metallic solids. THEORETICAL BACKGROUND Heat transfer by conduction is described by fourier’s law. Q x /A= -kdT/dx ------------------------------------------------------------- 1) where k is the thermal conductivity of the material which is a function of temperature for the case of solids. and Qx is the rate of heat transfer K = k o (1+ β T) ------------------------------------------------------------2) It is known that any two materials can not have a perfect contact between them , so when heat moves through this empty space there must be a temperature drop because of the resistance of air which has lower thermal conductivity than the solid material . this is called the barrier resistance which is defined as q x /A = ∆Τ b / 1 /h c-------------------------------------------------------------3) where ∆Τ b is the barrier temperature gradient and 1/ hc is the resistance the cross sectional area A will be a function of position x as in the eq. 4 q x /A(x)=-kdT/dx--------------------------------------------------------------4) the area of a circular cone r =.5(x=0) ,r=1(l=14) is A(x) = π{.5/ 12 +.5x/14 } 2 ------------------------------------------------------5) for a circular cone qx =(9.35e-3)*k(T h-T c )-----------------------------------------------------------6)...
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This note was uploaded on 12/30/2010 for the course CHEMICAL E CHE 309 taught by Professor M.elgaily during the Fall '09 term at King Fahd University of Petroleum & Minerals.

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H1 - INTRODUCTION heat transfer accrue in three ways...

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