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Effect of hydrodynamics on the production of pickering emulsions in unbaffled stirred tanks

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2019
Demirdoğan, Özge
An emulsion is a fluid system obtained by dispersing one of two immiscible liquids in the other. Since this formation is thermodynamically unstable, it has to be stabilized using an emulsifier. Emulsions in which solid particles are used as emulsifiers are called Pickering emulsions. In this study, the investigation of the effect of different hydrodynamic conditions on the production of Pickering emulsions in unbaffled stirred tanks was aimed. Oil in water Pickering emulsions were produced. Distilled water was selected as continuous phase and silicon oil was selected as dispersed phase. Hydrophilic solid glass beads were used as emulsifier. To observe the effect of different flow patterns, Rushton turbine (RT), down pumping pitched blade turbine (PBTD) and up pumping pitched blade turbine (PBTU), all at two different sizes were used. Shaft was positioned at three different locations: e/T=0, e/T=0.1 and e/T=0.2. Hydrodynamic parameters such as impeller tip speed, impeller Reynolds number, Weber number and power per mass ratio were changed to create different hydrodynamic conditions. The effect of these different hydrodynamic conditions on the production of Pickering emulsion was determined by analyzing drop size and drop size distribution with Malvern Mastersizer equipment. It was found that an increase in the eccentricity ratio causes a decrease in the size of the vortex, an increase in the contact of the impellers with the liquid in the tank and better transfer of performances of the impellers to the system. In general, increase in eccentricity ratio causes a decrease in drop size. The amount of energy dissipated into the system has an important effect on determining drop size of the emulsions. Generally, the smallest drops and the narrowest drop size distribution were obtained with RT T/3 at e/T=0.2.