The effect of surfactants on the initiation and development of air-water slug flow in hilly terrain pipeline

In hilly terrain pipelines, gas-liquid slug flow usually forms in the low-lying elbow and develops in the inclined ascending pipe at a low superficial liquid velocity and influences the effective and safe natural gas transportation. The surfactant additive has a significant effect on this flow and promotes the liquid drainage in hilly terrain pipelines. To further understand the interaction mechanism between surfactants and gas-liquid flow, an experimental investigation of the initiation and development of slug flow with and without surfactants was performed. The acrylic test tubes consisted of an inclined descending pipe, a horizontal pipe and an inclined ascending pipe with a 50 mm ID and inclination angles of +/- 10 degrees. The 100 parts per million (ppm) of sodium dodecyl sulfate (SDS) and 100 ppm of sodium dodecyl benzoyl sulfate (SDBS) were respectively used as surfactant additives in this work. The flow behavior of slug initiation and development was observed by a visual system and measured using multiple 2 MHz ultrasonic transducers in the elbow and inclined pipeline. The flow morphology of slug flow changed significantly with the foam formation in the air-surfactant solutions flow. The slug frequency, the liquid film and velocity variation and the velocity characteristics of slug flow were obtained and analyzed based on the measured echo and velocity profiles. The addition of surfactants weakened the strong gas-liquid interaction at the front of liquid slug and increased the velocity of backflow in the liquid film. The experiment results make the effect of surfactants on the gas-liquid interface and velocity characteristics of slug flow in hilly terrain pipelines more clear.