Two-group drift-flux model for dispersed gas-liquid flows in annuli

Interfacial area concentration (IAC) plays a vital role in mass, momentum, and heat transfers between gas and liquid phases in two-phase flows. The IAC of group -one bubbles, including spherical and distorted bubbles, differs from the IAC of group -two bubbles, including cap, slug and churn -turbulent bubbles. The two -group interfacial area transport equation (IATE) can be used as a mechanistic model to obtain the IAC of each group. The equation demands the two -group gas velocity fields, leading to the need to solve an extra momentum equation, which is complicated. The two -group drift -flux model can prevent this complexity by providing twogroup gas velocities without introducing the extra momentum equation. Despite the importance of gas -liquid flows in annuli, the drift -flux model for gas -liquid flows is not well -developed like it is for pipe flows. The main objective of this study is to develop a two -group drift -flux model for dispersed vertical flows in annuli. The two -group drift -flux model provides the flow characteristics of group -one and group -two bubbles, such as void fractions and velocities, which strongly affect the prediction of the available interfacial area concentration of the group -one and group -two bubbles for heat and mass transfer. Hence, after comprehensively investigating the available experimental data, this study first improves a one -group drift -flux model for dispersed gas and lowviscosity liquid upward flows in annuli and proposes a new two -group drift -flux model. Then, the models are evaluated using the respective group experimental data. The consistency between one -group and two -group driftflux models is also investigated. This consistency helps to reduce the two gas momentum equations to one gas mixture momentum equation. The results of the comparison between model predictions and experimental data are satisfactory.