CONDUCTION HEAT TRANSFERHeat TransferElectricalAnalogyFigure 2 Equivalent ResistanceExample:A composite protective wall is formed of a 1 in. copper plate, a 1/8 in. layer of asbestos,and a 2 in. layer of fiberglass. The thermal conductivities of the materials in units ofBtu/hr-ft-oF are as follows: kCu = 240, kasb = 0.048, and kfib = 0.022. The overalltemperature difference across the wall is 500°F. Calculate the thermal resistance of eachlayer of the wall and the heat transfer rate per unit area (heat flux) through the compositestructure.Solution:RCuDxCukCu1 in1 ft12 in240Btuhr ft °F0.000347hr ft2°FBtuRasbDxasbkasb0.125 in1 ft12 in0.048Btuhr ft °F0.2170hr ft2°FBtuRfibDxfibkfib2 in1 ft12 in0.022Btuhr ft °F7.5758hr ft2°FBtuHT-02 Page 10 Rev. 0
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