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Filmwise condensation measurements of steam were made on horizontal finned tubes under vacuum and near-atmospheric conditions. Data were obtained for copper tubes with fins of rectangular, triangular, trapezoidal, and parabolic cross sections, and for a commercially-available finned tube. A stainless steel finned tube was also tested to investigate the effect of thermal conductivity. Maximum enhancements of about 4.8 were obtained under vacuum conditions, and about 6.9 at atmospheric pressure, compared to a smooth tube having an outside diameter equal to the root diameter of the finned tubes. The optimum fin spacing was found to be about 2.0 mm for rectangularly shaped-fins with a fin thickness of 1.0 mm, and fin height of 0.5 and 1.5 mm. Fins with a parabolic shape were shown to perform better than fins of rectangular shape, and fins were shown to degrade the performance of stainless steel tubes. The effects of vapor shear were shown to have only a small influence on the steam-side heat-transfer coefficient. A theoretical model proposed by Webb et al. [25] was found to underpredict the experimental data. Several suggestions to modify this model are described. National Science Foundation Agreement No. MEA82-03567 http://archive.org/details/filmcondensation1094521341 National Science Foundation Agreement No. MEA82-03567 Lieutenant, United States Navy Approved for public release; distribution is unlimited. |
