The Transition Between Stratified and Intermittent Flows and Liquid Holdup Discontinuities in Slightly Upward Inclined Pipes

Identifying the transition from stratified flow to intermittent flow is important for slightly upward multiphase flow pipelines. The transition can be considered as the onset of liquid accumulation at low points in hilly terrain pipelines which may result in corrosion and slugging issues. In addition, flow pattern identification is critical for mechanistic modeling of pressure drop and liquid holdup predictions. In this paper, experimental results are presented detailing the transition region between stratified and intermittent flows and the critical gas velocities for the onset of liquid accumulation. The experiments were carried out in a 6-in ID pipe elevated at 2° upward for two-phase, air/water, flow at atmospheric pressure conditions. The experiments were set up to investigate gas condensate conditions at low liquid loading conditions in slightly upward inclinations. The results show an interesting behavior around the transition region which was not observed in smaller pipe diameters or higher operating pressure conditions. The phenomenon is related to the stability of stratified flow and the existence of multiple holdup solutions. An overview of the existence of multiple holdups region for the tested conditions is provided. In addition, the results are compared with model predictions for the critical gas velocities, pressure drop, and liquid holdup.