Experimental study of pseudo-slug flow in upward inclined pipes

Pseudo-slug flow occurs between the slug and segregated flows and occupies a non-negligible area in the flow pattern map especially for gas condensate pipeline/wellbore where the liquid flow rate is low. An experimental study was conducted in a 3-in. flow loop with a valley configuration to investigate pseudo-slug flow characteristics using wire-mesh sensors, which include total average liquid holdup, liquid holdups in pseudo-slug body, and film region, respectively, pseudo-slug frequency, body length, and structure velocities. Comparison with conventional slug characteristics shows that pseudo-slugs have lesser liquid holdup in slug body, shorter body lengths, and smaller structure velocities. The pseudo-slug characteristics were also compared with predictions from existing correlations for conventional slug flows, as no correlation is available for pseudo-slug flow. The comparison shows poor agreement as expected, which necessitates the development of correlations for pseudo-slug flow specifically. The spatial evolution of pseudo-slugs is also discussed. Two initiation and dissipation mechanisms are described based on the location where pseudo-slugs are initiated and dissipated. In general, pseudo-slugs are shorter and slower near the inlet of uphill section compared the farther downstream locations in the uphill section.