Drift-flux parameter modeling of vertical downward gas–liquid two-phase flows for interfacial drag force formulation

The two-fluid model has been adopted as a platform of nuclear thermal–hydraulic system analysis code because it can treat the mechanical and thermal non-equilibrium between phases through the interfacial transfer terms. Precise modeling of the area-averaged interfacial drag force in the interfacial momentum transfer term is essential in predicting void fraction accurately. The drift-flux parameters, such as the distribution parameter and drift velocity, play an essential role in formulating the area-averaged interfacial drag force. This study aims at developing a drift-flux correlation with a wide application range for vertical downward two-phase flows. First, over 1200 experimental void fraction data of vertical downward two-phase flows were collected from 13 sources. Then, the existing correlations of the distribution parameter and drift velocity were reviewed and examined. Finally, a new drift-flux correlation was developed based on a large amount of experimental data and state-of-the-art knowledge of two-phase flow behaviors. The comparison between the experimental and calculated void fractions by the newly-developed correlation demonstrated that the new correlation could achieve superior performance to the existing correlations. More than 93% of the predicted void fractions were predicted within ± 20% error with the mean relative deviation and mean absolute relative deviation of 0.609% and 9.93%, respectively.