(98at) Understanding the Dynamics of An Organic Droplet Released in Quiescent Water Column

Through this work, we have made an effort to understand the mechanisms involved when oil containing light end is released from deep water ruptured well as in the case of BP Deep water horizon spill. We present results from our experimental studies that mimic the rise and fall of the oil droplet due to dissolution of the lighter hydrocarbons. A model organic droplet composed of chlorobenzene (insoluble in water) and acetonitrile (soluble in water) has been used to study this phenomenon. The experimental setup consists of a tank filled with water and a nozzle through which the dispersed phase (organic droplet) is injected. The mixture density of organic droplet is adjusted (0.89-0.96g/cc) such that it is initially less than that of water. The droplet initially rises and starts losing acetonitrile to surrounding water phase. As a consequence, the density of the droplet increases gradually. A stage is reached when density of droplet becomes same as that of surrounding fluid and droplet becomes stationary. Further loss of acetonitrile causes the droplet to sink. A numerical model has also been developed to match the trajectory of droplet exhibiting the above phenomenon.

       As an extension to the above work, we have also analyzed the effect of surfactant addition on the dynamics of crude oil droplet. Experiments have been conducted in a tank with a capacity of about 100 liters with an oil droplet being released into the quiescent water column through a nozzle. The size of droplets is varied using nozzles of different diameters. The shape adopted by the emanating droplets varies from spherical to oblate. On addition of the surfactant (SDS) to water column the reduction of interfacial tension brings in variation in the internal circulation and causes the droplet to flatten. The change in droplet rise time, the time taken by droplet to reach the water- air interface serves as an observable parameter to support this variation in droplet dynamics. A numerical model based on Volume of Fluid method has been used to emulate the above experimental observations.