Review and Analysis of Current Gas-Liquid Drag Models at High Gas Fractions
Gas-liquid multiphase flow modeling is applicable to many aspects of industry specifically, gas-liquid and gas-liquid-solid reactors therefore, enhanced prediction methods are of interest to assist in improving current and future designs. For dispersed gas-liquid flow the momentum exchange between phases is critical to understanding and evaluating how the fluids interact. This work presents a review and analysis of currently available models for determining the momentum exchange in bubbly flow at high phase fractions. These drag correlations are often referred to as bubble swarm drag models. The determination of a slip velocity between gas and liquid phases is essential to determining process parameters such as gas holdup, surface area for heat and mass transfer, and convective heat transfer etc. In recent years, the proliferation of computation fluid dynamics (CFD), increased the need for accurate and robust methods for coupling phase momentum. When using CFD to model phase separation in industrial processes the result is sensitive to the chosen drag correlation and therefore reliable and robust correlations that are valid at high gas phase fractions are required. This study attempts to present the current bubble drag models available, highlight the conditions under which they are applicable, and perform a comparative analysis of the predictive capabilities for each correlation. Special attention is given to drag correlations suitable for modelling gas-liquid separation processes where model accuracy at high (>30%) gas fractions is required. Estimates of the relative magnitude of prediction differences for all reviewed correlations is presented demonstrating the sensitivity of analysis to the choice of drag models. In an effort to address the identified issues an alternate drag correlation framework is proposed to improve prediction accuracy in these regions.