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 - ft^{2} -^{o}F.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 (A_{o}), and the overall temperatureQdifference (DT_{o}) using the overall heat transfer coefficient (U_{o}). The overall heat transfercoefficient combines the heat transfer coefficient of the two heat exchanger fluids and the thermalconductivity of the heat exchanger tubes. U_{o} is specific to the heat exchanger and the fluids thatare used in the heat exchanger.(2-3)QU_{o}A_{oD}T_{0}where:= the rate heat of transfer (Btu/hr)QU_{o}= the overall heat transfer coefficient (Btu/hr - ft^{2} -^{o}F)A_{o}= the overall cross-sectional area for heat transfer (ft^{2})DTo= the overall temperature difference (^{o}F)BulkTemperatureThe fluid temperature (T_{b}), referred to as the bulk temperature, varies according to the details ofthe situation. For flow adjacent to a hot or cold surface, T_{b} is the temperature of the fluid thatis "far" from the surface, for instance, the center of the flow channel. For boiling orcondensation, T_{b} is equal to the saturation temperature.HT-02 Page 4 Rev. 0