Analysis, comparison and discussion on the utilization of the existing slug liquid holdup models to predict the horizontal gas-liquid plug-to-slug flow transition

In horizontal configuration, the gas-liquid intermittent flow can be plug or slug flows. Different works have demonstrated that the two-phase flow pattern, despite their similarity, are different. Thus, it is important to differentiate between them in order to develop more robust predictive models. The limit of the existing model to predict the plug-to-slug flows transition were demonstrated firstly. After that, eleven existing slug liquid holdup (HLS) models were used in order to test their potential utilization for predicting the plug-to-slug flows transition. Using HLS = 0.9 as the criterion to distinguish between the two regimes, the relationship between the superficial velocities of the two phases was generated. The obtained transition lines were compared with visual observations collected from several published works in order to test the predictions of each model, and for different operating conditions. It was concluded in this paper that the slug liquid holdup models can be easily used for this purpose. Meanwhile, the prediction level of each model depends on the pipe diameter and the viscosity of the liquid phase.