Modeling of interfacial area concentration and interfacial momentum transfer: Theoretical and experimental study

The interfacial transfer terms are important for modeling the dynamic coupling between the phases in a two-fluid formulation. The geometric factor of these transfer terms is recognized by the interfacial area concentration. An independent experimental study of the interfacial structure in adiabatic two-phase flow was carried out in a 25.4 mm ID pipe. The local void fraction, interfacial area concentration, interfacial velocity, bubble frequency, and Sauter mean diameter were measured by a double-sensor probe. The flow structure development was visualized by measuring the radial distribution of these phasic parameters at three axial locations (L/D = 12, 62, and 112). More detailed measurements in the fully developed flow were conducted at L/D = 120. The interfacial structure was measured by the double- and four-sensor probes. Other parameters such as the Taylor bubble film thickness, bubble length, and slug unit length in the slug flow regime were measured by a thin-film probe. A simplified one-dimension interfacial area concentration transport equation with only the coalescence sink term was presented. An analytical solution was obtained by using a self-similarity transformation. A set of data of interfacial area concentration decay from the flow development study was used to compare with the model predictions. The coalescence rate was determined by the results of the experimental results. For the interfacial momentum transfer, a multiparticle drag law was used to model the interfacial momentum transfer term. This term appeared in both gas and liquid momentum balance equations. In order to solve the momentum equations, it was necessary to close the system equations with a two-phase turbulent model and to set the boundary condition by a wall friction factor. An empirical mixing length model was proposed and computed from the experimental data obtained from the literature. The wall friction was calculated by the homogeneous equilibrium mixture model. The predicted gas and liquid velocities were compared with the experimental results. The gas and liquid velocities were measured by the double-sensor probe and hot-film anemometer, respectively. The model overpredicted the gas velocity in all cases. This is an indication that a higher interfacial drag is felt by individual bubble in the dispersed flow