Viscosity effect on drift-flux model for upward two-phase flows

The drift-flux model is of practical importance in predicting the void fraction of upward two-phase flows with high-viscosity liquid phase. This study aims to develop an accurate and robust drift-flux correlation for each type of upward high-viscosity two-phase flow to overcome the unsatisfactory predictive performance of the existing drift-flux correlations. First, an extensive literature review was conducted which collected more than 500 experimental void fractions of upward high-viscosity two-phase flows from 11 sources. The viscosity numbers for the collected database ranged from 0.0213 to 25.6. The existing drift-flux correlations of high-viscosity two-phase flows were critically reviewed. A comparison between the collected database and the existing drift-flux correlations indicated that none of the existing drift-flux correlations could predict the entire collected database with acceptable accuracy. The failure of the void fraction prediction using the existing drift-flux correlations drove the development of new drift-flux correlations based on the state-of-the-art understanding of the flow behaviors for upward high-viscosity two-phase flows. The rigorous constitutive equations of the drift velocities were formulated based on the drag law. The dependence of the distribution parameter on the physical properties and flow conditions was systematically analyzed. Finally, the new drift-flux correlation was developed for upward high-viscosity two-phase flows. This correlation was well-validated as demonstrating superior predictive performance to the existing correlations; for example, 92.2% of the collected void fractions were predicted within ±20% error without any systematic bias. The correlations are considered to have great practical potential in improving the analysis of high-viscosity two-phase flows.