Evaluating Performance of Two-Group Interfacial Area Transport Equation for Vertical Small and Large Diameter Pipes

In the two-fluid transport model, the coupling of mass, momentum and energy transfer between phases is highly dependent on interfacial area transfer terms. Several research efforts in the past have been focused on the evelopment of an interfacial area transport equation model (IATE), in order to eliminate the drawbacks of static flow regime maps currently used in best-estimate thermal-hydraulic system codes. The IATE attempts to model the dynamics that are involved in two phase flows by accounting for the different interaction mechanisms affecting bubble transport in the flow.
The further development and validation of IATE models has been hindered by the lack of adequate experimental data in regions beyond the bubbly flow regime. At the Helmholtz-Zentrum Dresden Rossendorf (HZDR) experiments utilizing wire mesh sensors have been performed over all flow regimes, establishing a database of high-resolution (in space and time) data. Two sets of data from small and large diameter pipes fitted with wire mesh sensors are utilized in this work. Analysis of flow conditions in the bubbly, churn turbulent and annular flow regimes is presented.
The performance of the Fu-Ishii two-group model is evaluated against small diameter database. Results indicate good performance (< 10% error) for small group 1 bubbles, and poor performance for large group 2 bubbles. The Smith two-group large diameter IATE model is evaluated for the large diameter database. In low void-fraction regimes, the Smith model performs well. In high void-fraction regimes, there is poor group-wise interfacial area prediction – however the total interfacial area is erroneously predicted well as group-wise errors compensate each other. Overall, the study suggests that further efforts and re-evaluation of closure terms are needed in order to extend the range of validity of the IATE models.