Numerical investigation on complete condensation and freezing of finned tube air-cooled condensers

•A conjugate heat-transfer model is applied to air-cooled condensers.•The complete condensation mechanism in freezing of finned tubes is investigated.•Factors affecting film formation and wall temperature are examined.•The study allows for design and operation of condensers for anti-freezing. The freezing of finned tubes degrades the safety and efficiency of air-cooled condensers in power plants, so it is beneficial to investigate the freezing mechanism and anti-freezing measures for condensers. A conjugate model-based approach is presented, which characterizes the thermodynamic development between the vapor and cooling air of finned tube condensers, indicating that freezing is essentially caused by an immediate decline of the cooling-wall temperature at the complete condensation. The influences of the atmospheric temperature, cooling-air flow velocity, and vapor inlet mass flux on the film formation and wall temperature are examined for complete condensation, finding that the film formation depends on the vapor mass flux, while the cooling-air flow velocity dominates, whether or not the wall temperature achieves the freezing point. The internal flow of Λ frames in condensers reveals the mechanism whereby a serious freezing attacks the middle and lower sections of finned tube bundles but frees the upper. An air flow guiding device is recommended for the anti-freezing of condensers. This study contributes to the design of anti-freezing condenser frames and the secure operation of field condensers.