Thermo-hydraulic model for steam condensation in a large, inclined, flattened-tube air-cooled condenser

A thermo-hydraulic model for calculating capacity, heat transfer coefficient and void fraction of an inclined air-cooled steam condenser is presented. The condenser tube has an elongated-slot cross-section, with inner dimensions of 214 × 16 mm. The model was developed for a 10.7 m-long tube, and validated by comparison with experiments in a 5.7 m-long tube. The model is for downward inclination angles from 0 to 90° with co-current vapor and condensate flow. The cooling air is in cross flow. This model is developed based on existing models for inclined, stratified-flow condensation. These have been adapted to the flattened-tube air-cooled condenser geometry and conditions. The model couples both air- and steam-side behavior in order to accurately resolve the variations in heat transfer coefficients, temperatures, and heat flux. On the steam side, the model is for stratified flow, and separates the flow into two sections: a falling film along the wall, and an axially-flowing condensate river along the tube bottom. The axially-flowing condensate river is modeled using open-channel-flow theory. On the air side, heat transfer coefficient is determined from a combination of empirical correlation and CFD. The model and experimental results show agreement within 5% for capacity and 20% for void fraction for all tube inclinations.