An empirical approach for predicting slug to pseudo-slug transition of air/water upward two-phase flow

Pseudo-slug (PSL) flow is an intermittent flow that has short, frothy, and chaotic slugs, which are not fully formed and have a structure velocity that falls between the conventional slug translational velocity and the wave celerity. It is important to predict the transition from conventional slug (SL) flow to PSL to determine the pressure gradients and liquid holdups. Literatures revealed that PSL can comprise a significant portion of the conventional flow pattern map, especially in highly deviated large-diameter (D) wellbores and pipelines. Several studies investigated the behavior of PSL; however, certain models were developed to predict SL/PSL transition. In the present study, an empirical model is derived employing the modified gas and liquid Froude numbers in measured dataset of Zhu (2019). The dataset consists of 125 data points, covering inclination angle (θ) from 2° to 89.4° with D of 0.1016 m. The range of superficial gas velocity is 0.124–3.313 m/s, with a constant liquid superficial velocity of 0.05 m/s. The suggested model accurately predicts all the data points and captures the expected effects of θ, D, and the gas density on the SL/PSL transition. The proposed model predicted well when validated against several independent experimental studies.