Effect of surfactant additive on vertical two-phase flow

• The maximum liquid holdup reduction caused by surfactant occurs in churn flow.
• The maximum pressure drop reduction caused by surfactant occurs in slug flow.
• Drag reduction caused by the surfactant additive is beyond 100% in some cases.
• The effectiveness of surfactant-assisted lifting depends on gas–liquid ratio.
• The negative frictional pressure drop found here challenges the general sense.

The effect of surfactant on vertical gas–liquid two-phase flow was experimentally simulated in a low pressure apparatus. Liquid holdup reduction, pressure drop reduction and drag reduction caused by a surfactant additive were investigated. The flow patterns cover bubbly, slug, churn and annular-mist flows. The results show that the maximum liquid holdup reduction induced by the surfactant additive is high up to 88.6% which appears in churn flow. The maximum pressure drop reduction induced by the surfactant additive is high up to 96.5% which occurs in slug flow. Drag reduction caused by the surfactant additive is unexpectedly beyond 100% in some cases of vertical two-phase flow at high gas–liquid ratios. The frictional pressure drops are found to be negative for some vertical two-phase pipe flows at high gas–liquid ratios, challenging the general sense that the frictional pressure drop should be positive in pipe flow. The surfactant additive does not have significant effect on the transition of two-phase flow pattern. But the surfactant additive makes considerable impact on the detailed configurations of two-phase flow. The surfactant-assisted flow improvement is dependent on gas–liquid ratio, gas velocity and two-phase flow pattern.