Hydrodynamic Study of a Rising Bubble in the Presence of Cetyltrimethylammonium Bromide Surfactant

The performance of surfactants especially in two-phase systems, depends on their type, Hydrophile-Lipophile Balance (HLB) number, concentration, and whether the surfactant is ionic or non-ionic. The current work was conducted to study the effect of the presence of Cetyltrimethylammonium Bromide (CTAB), a cationic surfactant, in air-water systems. Thus, the behavior of a single air bubble rising in aqueous CTAB solutions was studied experimentally. The independent test variables are solution concentration (0.4-1.6mM) and bubble diameter (3.5-4.6mm). The effect of these variables on rising velocity, bubble shape, and drag coefficient has been studied. Due to the importance of the drag coefficient in two-phase fluid, the effect of Reynolds number, Eötvös number, and aspect ratio on it has also been evaluated. Experiments have been performed at high Reynolds numbers (850<Re<1000), which are obtained by increasing the surfactant concentration. The results showed that the selected ionic surfactant had a more tangible effect on bubble behavior than nonionic surfactants. Moreover, there is no noticeable difference in the behavior of the bubble rising at concentrations above and below of Critical Micelle Concentration (CMC) of CTAB, which can be attributed to its high aggregation number compared to other surfactants.