HEAT TRANSFER TERMINOLOGYHeat TransferConvectiveHeatTransferCoefficientThe convective heat transfer coefficient (h), defines, in part, the heat transfer due to convection.The convective heat transfer coefficient is sometimes referred to as a film coefficient andrepresents the thermal resistance of a relatively stagnant layer of fluid between a heat transfersurface and the fluid medium. Common units used to measure the convective heat transfercoefficient are Btu/hr - ft2 -oF.OverallHeatTransferCoefficientIn the case of combined heat transfer, it is common practice to relate the total rate of heattransfer ( ), the overall cross-sectional area for heat transfer (Ao), and the overall temperatureQdifference (DTo) using the overall heat transfer coefficient (Uo). The overall heat transfercoefficient combines the heat transfer coefficient of the two heat exchanger fluids and the thermalconductivity of the heat exchanger tubes. Uo is specific to the heat exchanger and the fluids thatare used in the heat exchanger.(2-3)QUoAoDT0where:= the rate heat of transfer (Btu/hr)QUo= the overall heat transfer coefficient (Btu/hr - ft2 -oF)Ao= the overall cross-sectional area for heat transfer (ft2)DTo= the overall temperature difference (oF)BulkTemperatureThe fluid temperature (Tb), referred to as the bulk temperature, varies according to the details ofthe situation. For flow adjacent to a hot or cold surface, Tb is the temperature of the fluid thatis "far" from the surface, for instance, the center of the flow channel. For boiling orcondensation, Tb is equal to the saturation temperature.HT-02 Page 4 Rev. 0
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