Pseudo-slug flow is a sub-regime of intermittent flow that is characterized by short, undeveloped, frothy chaotic slugs, with translational velocity less than the mixture velocity of the fluids. Pseudo-slug flow does not comply with the basic characteristics of conventional unit-cell slug flow where liquid blocks the entire pipe cross-sectional area, and liquid is scooped at slug front, transferred to slug body, and shed back to liquid film. The liquid in pseudo-slug body is insufficient to reach the upper part of the pipe wall, resulting in only large wave with entrained gas bubbles at the bottom part of the pseudo slug body. Consequently, a significant reduction in the gas phase flowing area above the wave is formed, which increases the local gas velocity, entraining large volume of liquid droplets in the upper part of the slug body. Therefore, the pseudo-slug body can be divided into two regions, liquid film (wave) with entrained gas bubbles at the bottom, and gas core with entrained liquid droplets. The objective of this study is to develop a plausible physical model of the experimentally observed pseudo-slug liquid holdup phenomenon and model the physical and hydrodynamic behavior using a dimensional regression modeling approach.

This paper discusses liquid and gas entrainment mechanisms within pseudo-slug body based on experimental observation. Previous experimental results show that the proposed dimensionless groups; namely, Stokes, Slippage, and Poiseuille are strongly correlated to pseudo-slug body liquid holdup experimental data and are capable of describing the experimentally observed physical behavior. A linearized regression model is developed to combine the liquid holdup proportionally in both regions of the pseudo-slug body (mentioned above) and correlate them to the experimentally measured total pseudo-slug liquid holdup using wire mesh sensor. A validation study of the proposed model with Fan (2017) experimental data shows good agreement, outperforming all other existing slug liquid holdup correlations.

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