Local condensation heat transfer coefficient inside a circular vertical tube was experimentally measured for the design purpose of an air-cooled shell and tube heat exchanger in long term passive cooling system. An experiment was conducted in a 1/2500-volume scaled-down model of the emergency cooldown tank (ECT) of the system integrated modular advanced reactor (SMART). While saturated vapor downstream (Re_f < 30) flows in the shell side, air natural upstream flows in the tube side. The inner diameter and length of the tube were 261.4 mm and 1.8 m. The outer diameter of the shell was 318.5 mm. Eleven thermocouples were installed at 150 mm apart alongside the outer wall of SUS plate, a thickness of 3 mm, between vapor and air streams. During a performance evaluation of the shell and tube heat exchanger, the heat loss from the emergency cooldown tank was approximately 30% of the total heat load from 1.2 to 1.4 kW. Local condensation heat transfer coefficients were reduced by the Nusselt equation with ranging the quality from I to 0. With the range of mass flux from 0.1 to 0.2 kginrls, condensation heat transfer coefficients were distributed at 110 ~ 350 W/m~2/K. The experimental data was compared to the existing condensation heat transfer correlations. Among those, Shah correlation gave the best prediction of current experimental data with 54% average error. To increase the accuracy, new correlation is proposed based on the Dittus-Boelter equation and local quality in this study. New proposed correlation predicts current experimental data with 10% average error.
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