One-dimensional drift-flux model for two-phase flow in NaCl solutions: The role of surface mobility

The presence of dissolved salts in water inhibits bubble coalescence, facilitating the generation of microbubbles, while also maintaining a tangentially mobile air-water surface. In this study, we investigated the variation of bubble size and gas holdup with gas velocity in NaCl solutions using a rectangular bubble column and interpreted the experimental data using the one-dimensional drift-flux model. For the generated bubbles at the size between 0.4 mm and 1 mm, we found that the Moore model assumes mobile air-water surfaces, rather than the Schiller and Naumann model, should be used to describe the bubble terminal velocity. The latter model, which assumes an immobile air-water surface, has been used successfully to predict two-phase flow in surfactant solutions but would overestimate the gas holdup by almost 100 % for NaCl solutions. This finding emphasizes the crucial role of surface mobility in determining gas holdup. Thus, we propose the use of a one-dimensional drift-flux model, incorporating the Moore model to describe bubble terminal velocity, for microbubble systems with a mobile air-water interface.