When dealing with heat transfer across heat exchanger tubes, an overall heat transfer coefficient, U_{o} , must be calculated. Earlier in this module we looked at a method for calculating U_{o} for both rectangular and cylindrical coordinates. Since the thickness of a condenser tube wall is so small and the crosssectional area for heat transfer is relatively constant, we can use equation below to calculate U_{o} . Example: Referring to the convection section of this manual, calculate the heat rate per foot of tube from a condenser under the following conditions. = 232 deg F. The outer lm diameter of the copper condenser tube is 0.75 in. with a wall thickness of 0.1 in. Assume the inner convective heat transfer coefficient is 2000 Btu/hrft^{2} (deg) F, and the thermal conductivity of copper is 200 Btu/hrftEF. The outer convective heat transfer coefficient is 1500 Btu/hrft (deg) F.
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