Liquid Entrainment in Annular Gas/Liquid Flow in Inclined Pipes

Entrainment fraction is one of the key parameters in many applications, including wellbore and flowline design, separator design, wellbore loading, and corrosion inhibition. This study provides the first comprehensive entrainment data and their critical analysis for a full range of inclination angles ranging from horizontal to vertical in 76.2-mm-internal-diameter (ID) pipes. Experiments were conducted to investigate the effect of pipe inclination on entrainment fraction in air/water annular flow with inclination angles of 0, 10, 20, 45, 60, 75, and 90 degrees from horizontal. Two techniques were used to measure the entrainment fraction: film removal and isokinetic sampling. The experimental results were compared with existing models and correlations, and the best predicting methods were determined for all flow orientations. An inclination effect on entrainment fraction was observed. This effect occurred at low superficial gas velocities and was more prominent for higher superficial liquid velocities. Using the present study data, the Paleev and Filipovich (1966) correlation was found to be the most accurate in predicting entrainment fraction.. On the basis of all available data, the Pan and Hanratty (2002b) correlation performed the best in predicting entrainment fraction in all pipe orientations. For vertical annular flow, the Oliemans et al. (1986) correlation predicted entrainment fraction more accurately. The Pan and Hanratty (2002b) correlation was the most accurate in predicting entrainment fraction for horizontal annular flow. The Wallis (1969) correlation and the mechanistic model developed by Mantilla (2008) most accurately predicted the entrainment fraction for inclined annular flow.