Two-group interfacial area transport equation for a confined test section
To provide a closure relation for interfacial area concentration in the two-fluid model, two-group interfacial area transport equation is established, by which the change of interfacial area concentration can be dynamically predicted. In the current study, the sources/sinks in the two-group formulation are developed particularly for a confined test section by analytical modeling of the complicated intra-group and inter-group bubble transport based on five bubble interaction mechanisms. Group 1 bubbles include spherical/distorted bubbles while Group 2 are cap/slug/churn-turbulent bubbles. The modeled mechanisms are bubble coalescence due to random collision driven by turbulent eddies, bubble coalescence through wake entrainment, bubble breakup due to turbulent impact, large bubble breakup due to surface instability, and small bubble shearing-off at the rim of large bubbles. Due to the significant differences of the bubble size and shape, a systematic and comprehensive integral approach is applied in the modeling process. Experiments are performed to build a reliable database in an existing test section designed for distortion-free visualization of flow regime transitions. To determine flow conditions for the local measurements, flow regime transitions are identified by flow visualization. In total, 13 flow conditions are examined in cap-turbulent/churn-turbulent flow. The local two-phase flow parameters for each group of bubbles, such as void fraction, interfacial velocity, interfacial area concentration, etc., are acquired by four-sensor conductivity probes. Furthermore, the two-group interfacial area transport equation is evaluated against the experimental data in 11 bubbly and 13 cap-turbulent/churn-turbulent flow conditions. The adjustable model coefficients are determined based on a systematic approach by accounting for the previous one-group transport equation study, the current inter-group void transport and two-group interfacial area concentration transport. The average relative difference for the total interfacial area concentration between the experimental data and the model predictions in the 24 flow conditions is 6.68%. For the 13 cap-turbulent/churn-turbulent flow, the average relative errors of interfacial area for Group 1 and Group 2 bubbles are 7.54% and 21.15%, respectively. The evaluation results demonstrate that the two-group interfacial area transport equation focused on the current confined test section has the capability to well predict the interfacial area concentration in the bubbly, cap-turbulent flow, and churn-turbulent flow regimes.
Ishii, Purdue University.
Nuclear physics|Mechanical engineering|Chemical engineering
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