Dispersion and mixing dynamics of bilgewater emulsions in Taylor Couette flows

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The seminal study by G.I Taylor (1923) has inspired generations of work in exploring and characterizing Taylor-Couette flow instabilities and laid the foundation for research of complex fluids systems requiring a controlled hydrodynamic environment. Here, Taylor-Couette flow with radial fluid injection is used to study the mixing dynamics of complex oil-in-water emulsions. Concentrated emulsion simulating oily bilgewater is radially injected into the annulus between rotating inner and outer cylinders, and the emulsion is allowed to disperse through the flow field. The resultant mixing dynamics are investigated, and effective intermixing coefficients are calculated through measured changes in the intensity of light reflected by the emulsion droplets in the solution. The intermixing coefficients increased with inner cylinder Reynolds number, with even higher rates with salt present. Droplet size distributions (DSD) of emulsions were measured to determine the effects of timescale, mixing rates and salinity on the stability of emulsion stability Shear induced coalescence at lower intermixing and shear rates leads to higher mean volume diameters in the initial and final mixing stages. Emulsion destabilization over time leads to reduction of Dmv due to creaming out of larger oil droplets from the solution. whereas salinity reduced the IFT leading to smaller droplets in the initial mixing stages with lower number of coalescence events, while in the final stages salting out effects destabilized the emulsion due to aggregation and creaming. Ultimately, for these complex oily wastewater systems, formation of larger droplets yield better for separation during water treatment, and the final DSD observed here is found to be tunable based on salt concentration, observation time, and mixing flow state in the Taylor-Couette cell.

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