Two-group approach to develop drift-flux model for downward dispersed two-phase flows

The two-fluid model is extensively applied in the analysis of gas-liquid two-phase flows. A key parameter in this model is the interfacial area concentration (IAC), representing the total interface area per unit mixture volume, which is critical for formulating interphase mass, momentum, and energy exchange in conservation equations. Accurate prediction of IAC necessitates the consideration of the bubble-size spectrum in the IAC model. Considering a simple enough approach to avoid increased computational costs, a two-group framework has been proposed. In this two-group framework, spherical and distorted bubbles are assigned to group one, whereas cap, slug, and churn-turbulent bubbles are assigned to group two. The two-group void fractions are indispensable as key input parameters to estimate IAC. This study aimed to develop a two-group drift-flux model for vertically downward gas-liquid flows to predict two-group void fractions. First, the database of the two-group void fractions of vertically downward two-phase flows was developed based on 52 data points collected from 4 sources. Next, the flow behaviors for each group bubble were analyzed. The behaviors included the onset of group-two bubble formation and distributions of total void fraction, group-one void fraction, and group-two void fraction. Subsequently, the two-group drift-flux model, composed of the distribution parameters and drift velocities for each group, was established for vertically downward two-phase flows. The comparison results between the developed model and the collected data indicated that most void fraction data were predicted within ±10 % errors. The developed two-group drift-flux model is anticipated to enhance the analysis of downward two-phase flows. © 2025 Elsevier Ltd.