Steam condensation on a circular tube in the presence of non-condensables (air) in passive containment cooling system

Abstract

Steam inside the containment should be condensed to reduce the system pressure after severe accidents such as loss of coolant accident (LOCA) and main steam line break (MSLB). Due to the absence of an active coolant system, the passive containment cooling system (PCCS) can be used to improve safety by condensing the steam on a test section (coolant) tube surface. However, the steam condensation is degraded by the presence of non-condensable gases like air. The condensation heat transfer coefficient is dependent on operating parameters such as system pressure, air-mass fraction, and wall subcooling and geometric parameters such as tube diameter, tube length, and angle of orientation.In the present study, experiments are conducted on a vertical tube to estimate the condensation heat transfer coefficient in the presence of air. The system pressure ranges from 2 - 5.5 bar, air-mass fraction of 0.3 - 0.8 and wall subcooling of 27 - 80°C. The influence of test section tube diameter (48.2 mm, 32 mm, 22 mm, and 16 mm) and inclination angles (90° and 68° from the horizontal) are investigated. Based on the experimental data, a correlation for condensation heat transfer coefficient in terms of system pressure, air-mass fraction, wall subcooling, tube diameter and angle of inclination is proposed. The condensation heat transfer coefficient increases with the increase in the system pressure and decreases with the increase in the air mass fraction, wall subcooling and condenser tube diameter. With the decrease in the diameter of the vertical condenser tube from 48.2 mm to 16 mm, an increase in the condensation heat transfer coefficient of 66% is observed. A non-dimensional correlation for condensate Nusselt number as a function of Grashof number, air-mass fraction and Jakob number is also proposed. This correlation predicts 80% and 90% experimental data within 20% and 30% uncertainty range, respectively.