Experimental study using advanced diagnostics to investigate slug aeration and bubble behavior in high liquid viscosity horizontal slug flow

Abstract

Accurate prediction of slug liquid holdup is critical for accurate calculation of pressure gradient and average liquid holdup in pipes. However, most of the existing slug liquid holdup models are only accurate for a specific range of operating conditions, pipe dimensions, and fluid properties. The majority of these models are empirical, lacking the physical basis of slug aeration mechanisms. In this study, bubble entrainment mechanisms, bubble trajectories, and bubble loss from the slug body were identified. The experimental results from the high-speed camera (HSC) and particle image velocimetry (PIV) enabled detailed investigation of bubble entrainment mechanisms at slug front, bubble deformation and trajectories in slug body. These experimental observations were further analyzed and related to operating conditions and fluid properties. A horizontal 50.8-mm (2-in.) inner diameter (ID) pipe, and high viscosity liquid/air-fluid system (μL ≈ 0.51, 0.68 and 0.96 Pa s) were utilized. Experimental results revealed that the rate of gas entrainment at slug front, the bubble deformation in the slug body, and the number of fragmented bubbles in the slug unit all increase as mixture velocity and liquid viscosity increase, and as surface tension decreases. The proposed slug aeration mechanisms, and bubble behavior and characteristics in the slug body can form the basis for further mechanistic modeling of slug liquid holdup and other parameters required for proper slug flow modeling.