Modeling interfacial area concentration for boiling flow systems

Accurately modeling the interfacial area concentration (IAC) or Sauter mean diameter (SMD) is critical for robust analyses of boiling two-phase flows. IAC is closely related to the void fraction (VF) and SMD, i.e., IAC = 6 × VF/SMD. Since reliable one-dimensional drift-flux correlations are available to predict VF, IAC can be determined, provided SMD is accurately predicted. This study introduced a new methodology that systematically developed an SMD model for boiling flows by incorporating bubble Reynolds number, viscosity number, VF, and density ratio as key parameters. The model validation was conducted for a wide range of flow conditions, consisting of both subcooled and saturated boiling flows (thermal equilibrium quality from −0.3 to 0.1), different channel geometries (circular pipes, subchannels, and annuli) and fluid media (water, R-113, and R-12), hydraulic diameters of 17.7–34.6 mm, superficial gas velocities of 0.01–2.4 m/s, superficial liquid velocities of 0.16–2.8 m/s, VF of 0.01–0.47, pressures of 0.10–2.7 MPa, mass fluxes of 150–3000 kg/m²s, and density ratios of 0.0006–0.17. The proposed model captured distinct behaviors of SMD against VF and demonstrated excellent predictive performance with good agreement between predictions and experimental data. The mean absolute percentage errors for SMD and IAC predictions were 19.0 % and 22.9 %, respectively, indicating their high reliability.