Semester

Fall

Date of Graduation

1998

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Rakesh K. Gupta.

Abstract

During the flow of an emulsion, droplets of the dispersed phase can deform, breakup, coalesce or migrate to other regions within the flow field. Understanding these different processes, both individually and jointly, is relevant, for example, to the development of morphology in immiscible liquid-liquid systems such as polymer blends formulated using single screw or twin screw extruders. While deformation and breakup have been well researched for single drops, migration occurs only for concentrated emulsions. In this study, dilute emulsions of silicone oil and castor oil were employed to observe drop coalescence in the absence of drop breakup; flow fields utilized were Poiseuille flow through a tube and Couette flow in a cone-and-plate device. The influence of variables such as the continuous phase viscosity, the viscosity ratio, concentration of the dispersed phase, shear rate, the time of shearing, and temperature was studied.;By measuring the average droplet size under steady state conditions, it was found that the extent of coalescence was not influenced by the spatially non-homogeneous nature of the flow field; results correlated very well with the average shear rate. Other results were that coalescence could be promoted by increasing the concentration of the dispersed phase, decreasing the viscosity of the continuous phase, lowering the shear rate and reducing the temperature. In quantitative terms, it was found that available coalescence theory gave the correct order of magnitude for the average droplet size as a function of the imposed shear rate, but the actual variation of drop size with shear rate was gentler than that predicted by the theory.

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