Experimental and numerical investigations on the air-steam mixture bubble condensation characteristics in stagnant cool water

In this study, condensation of air-steam mixture bubble with mass fraction of steam above 0.5 was investigated first by a visual experiment at atmosphere. Then a 3-D numerical model based on volume of fluid (VOF) model and species model was developed to simulate the bubble condensation. In order to model steam condensation, mass and energy transfer between phases were modeled as source terms of conservation equations, using a correlation obtained from the experiment to predict the condensation heat transfer coefficient (HTC). After validation of the numerical model with the experimental results, influences of steam fraction and diameter of bubble on condensation characteristics are studied numerically. Moreover, steam concentration distribution in bubble was also analyzed along the time series of bubble condensation process. It was found that condensation HTC decreases with the increase of bubble diameter. With increase of steam fraction in bubble, the bubble volume shrinks more quickly due to the increased condensation rate, and the bubble accelerates more quickly reaching a higher terminal velocity. Aggregation of non-condensable air inside the bubble near the gas and water interface deteriorates the condensation heat and mass transfer.