Surfactant decreases the oil-water interfacial tension and thus oil droplets breakup into smaller ones and are dispersed into the water column. This paper presents the analysis of surfactant (premixed with oil droplet and bulk separately) on the oil droplet behavior in the water column. We implemented additional equations to account for the oil-water interfacial tension due to the presence of surfactant and those equations were incorporated into FLUENT by using UDF (User Defined Function). The streamlines around the oil droplet show major recirculation both inside and outside the oil droplet. It is noticed that the surfactant concentration is higher at the bottom and edges of oil droplet due to the shear effect. The presence of surfactant affects the deformation process of oil droplets of different diameters: Oil droplet with larger diameter (e.g., 4 mm in diameter) deforms into flat shape and breaks up. Tip-streaming is noticed and the droplet continue to rise up in jelly-fish like shape. However, much smaller droplets (e.g., 20 μm in diameter) only deform into oval shape and do not continue to breakup under the condition of same initial surfactant concentration. The presence of surfactant also deceases the rising speed of oil droplet compared to the terminal velocity of clean oil droplet. The results may be valuable to help us to apply surfactant to oil spill in a more efficient way.

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