Comprehensive evaluation of two-group interfacial area transport equation and new intergroup transfer model

Abstract

Interfacial Area Transport Equation (IATE) is developed to dynamically capture the flow structure change and predict Interfacial area concentration (IAC) for various flow regimes. Some recent experimental results show developing flows with intensive bubble coalescence at bubbly to slug transition in small pipes. The drastic IAC decreasing due to bubble coalescence under such conditions has not been well studied in previous IATE benchmark efforts, therefore it may not be captured by the current constitutive models for IATE. In this work, a comprehensive evaluation of the state-of-the-art two-group IATE models is performed using the small pipe data collected at bubbly and slug flow with a focus on transition. The evaluation result shows unsatisfactory performance in predicting the developing flow with intensive bubble coalescence at bubbly to slug transition. The reason is the underestimation of intergroup transfer from group I bubbles to group II bubbles. To improve the IATE performance, a new intergroup wake-entrainment model is developed to enhance the prediction capability for the intergroup void and IAC transfer. The new model incorporates a transition function derived based on the log-normal bubble size distribution and the lift force effect on bubble movement for group I bubbles, which allows for a smooth transition from bubbly to slug flow. The new intergroup transfer model significantly improves the IATE prediction capability in the 25.4 mm ID pipe and its applicability on other types of flow channels including 50.8 mm ID pipe and 200 × 10 mm duct is also verified.