Modeling two-group interfacial area concentration for dispersed gas-liquid flows in medium-to-large pipes

In the two-fluid model, the mathematical product of the interfacial area concentration (IAC) and the driving potentials determines the mass, momentum, and energy transfers between the two phases. Accurate IAC modeling is crucial for predicting the interfacial transfer phenomena in gas-liquid two-phase flows in medium-to-large pipes. Bubble behavior varies depending on bubble size, leading to their classification into two groups, G1 and G2. The existing two-group (2G) IAC models implemented in the one-dimensional system analysis codes, TRACE and RELAP5, exhibit significant limitations in predicting void fraction (VF) and Sauter mean diameter (SMD) for both G1 and G2 bubbles, resulting in unreliable IAC estimations. This study developed an improved 2G IAC model designed specifically for medium-to-large pipes to overcome these deficiencies. A 2G drift-flux correlation was introduced to predict G1 and G2 VFs for different flow conditions without requiring flow regime transitions. New G1 and G2 SMD models were also formulated using 158 data points collected from medium-sized pipe experiments and 121 data points collected from large-sized pipe experiments previously reported in the literature. The newly developed model demonstrated superior prediction performance compared to TRACE and RELAP5. The mean absolute percentage errors (MAPEs) for G1 and G2 SMDs were 19.3 % and 31.3 %, respectively, while the MAPE for the total IAC (the sum of G1 and G2 IACs) was 32.3 %. The model was validated across a wide range of flow conditions, covering superficial gas velocities from 0.083 to 8.4 m/s, superficial liquid velocities from 0.050 to 4.0 m/s, and pressures between 0.10 and 0.75 MPa, thereby ensuring its applicability in diverse operating scenarios. © 2025 Elsevier Ltd