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BF1-Ch01

# BF1-Ch01 - MEM 345 HEAT TRANSFER Heat A form of energy that...

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MEM 345 HEAT TRANSFER Heat: A form of energy that appears only in transit (recall work and heat interactions in your study of thermodynamics) What is meant by ‘heat transfer’? “Heat Transfer is energy in transit due to temperature difference” For engineering applications, knowing just the amount of heat transferred is not enough! A very important factor is the ‘heat transfer rate’

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Why study heat transfer? The problem of determining heat transfer rate is important in many branches of science and engineering. Examples: Design of ‘heat exchangers’ such ax boilers, condenser, radiators etc. Prevent burnout of nuclear reactor cores. Cooling of automobile engines, computers . How is heat transferred? Heat can be transferred by three different modes: CONDUCTION, CONVECTION and RADIATION
fig_01_01 fig_01_01

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Physical Origins & Rate Equations Conduction The mode of heat transfer in which energy exchange takes place from the region of high temperature to the region of low temperature ~ by the kinetic motion or direct impact of molecules. ‘Conduction is the only mode of heat transfer in opaque solids.’ Metals: good conductor (large number of free electrons) Conduction is also possible in stationary fluid having temperature difference. Rate equation of conduction Fourier’s law x dT q dx d d x dT q k dx d =- k is thermal conductivity.
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