Intermittent flow initiation in a horizontal tube: quantitative visualization and CFD analysis

The onset of slugging in stratified gas–liquid flow in a 26.4-mm ID horizontal pipe was investigated experimentally using a high-speed digital video processing technique. Spatio-temporal displacement maps were produced to show the evolution of two-phase flow structures (waves, slug precursors and liquid slugs) in the flow entrance region of the air–water mixture flow. The two-phase distribution derived from the visualization technique was in good agreement with measurements performed using non-intrusive capacitance sensors. Numerical results from a hybrid CFD approach that combined the two-fluid model and volume-of-fluid method to track the position of the large-scale interface in time and space also agreed well with the quantitative flow visualization data for phase distribution, slug length and slug frequency. The relative errors between the flow structure velocities calculated by cross-correlating the numerical and experimental (image analysis) phase distribution signals were 6.8 and − 7.4% for the slug and plug flow cases, respectively