Integrating the two-group drift-flux and Sauter mean diameter models to predict the interfacial area concentration for gas-liquid flows in large-diameter pipes

In two-phase gas-liquid dispersed flows, RELAP5/MOD3 calculates the interfacial area concentration (IAC) as the summation of two IAC components, IACs for (a) small bubbles (group one, G1) and (b) large bubbles (group two, G2). This approach requires the void fractions and Sauter mean diameters of G1 and G2 bubbles. This study evaluated the RELAP5/MOD3 IAC model for large-diameter pipes using experimental data measured in a void fraction range from 0.16 to 0.68 and for pipe diameters of 0.152 m, 0.203 m, and 0.304 m. The results showed 134% of the mean relative absolute error for the RELAP5/MOD3 IAC model. The RELAP5/MOD3 could not predict IAC when used for large-diameter pipes. This study developed the IAC model to enhance the predictability of the RELAP5/MOD3 model for large-diameter pipes. The developed model consisted of (a) a flow regime-independent model based on the two-group drift-flux model to obtain void fractions for each group and (b) Sauter mean diameter models for each group derived based on the improved critical Weber number approach and interfacial drag force approach depending on bubble group. The mean relative absolute error of IAC prediction was 17.1%. © 2025 Elsevier Ltd.