Drainage-induced Marangoni flows in circular tubes and the double role of surface tension

In this study, the drainage-induced Marangoni effect of Sodium dodecyl sulfate (SDS) (concentration 1.44 g/L) added aqueous Methylene blue solution (concentration 0.1 – 10 g/L) was studied in circular tubes of variable diameter (within the order of 1mm). During the drainage process, we hypothesize that the sudden conversion of hydrostatic to inertial drainage imparts a gradient of SDS concentration on the surface causing a Marangoni-induced film climbing due to the surface tension gradient. The upward climbing velocity diminished with decreasing tube diameter indicating that capillarity due to the meniscus dampens the inertial impulse upon drainage, reducing the SDS concentration gradient and thus the Marangoni force.