Numerical study on the interfacial heat and mass transfer characteristics of bubble direct contact condensation with the effect of non-condensable gas

Bubble condensation is one of the fundamental issues in the direct contact condensation, which is also affected significantly by the existence of non-condensable gas. In this study, a further investigation is carried out on air-steam bubble condensation with the Proportion Integration Differentiation (PID) control model which adjusts the mass transfer coefficient of Lee model in each time step by comparing the parameters obtained in the simulation with the ones calculated based on the empirical correlations originated from the experiments. Furthermore, species transport equations are employed to obtain the local mass fractions of steam and air. The proposed simulation schema is verified by the existing experimental data. Results show that the air-steam bubble condensation can be divided into initial and stable stages. The mass transfer coefficient used in Lee model can be regarded as linear growth over time at each stage, but with different slopes. The non-condensable gas can weaken the heat and mass transfer of condensation, but stabilize the bubble deformation. The present study also reveals the influences of subcooling and initial bubble diameter on the air-steam bubble condensation, which is expected to be instructive for better understanding the effect of non-condensable gas on the interfacial characteristics of bubble condensation in subcooled water.