Thesis (Ph. D.)--University of Minnesota, 1989. / Includes bibliographical references.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Ari Glezer; Committee Member: Bojan Vukasinovic; Committee Member: Mark Costello. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2009. / Emulsion explosives are classified as highly concentrated water-in-oil emulsions with high droplet volume fraction that exceeding the close packing limit of spherical droplets. These emulsions are commonly used as re-pumpable materials. Thus, the shearing action resulting from the transportation process of these materials has a tremendous impact on their structures and functionality and might reduce the shelf-life and performance of the products. Therefore the main goal of this research was to investigate the stability of highly concentrated water-in-oil emulsion under shearing using a newly designed piston-pumping instrument. The results of measurement included the droplet size distribution, microscopic observation, flow and viscoelastic properties of the materials. Neither crystallisation nor other destabilisation phenomena such as coalescence, partial coalescence, or phase inversion occurred during the shearing process of these emulsions, regardless of their formulation content. It was found that the high shearing action within this research experimental window induced droplet refinement. The changes in droplet size distribution were achieved by multipass flow through a small orifice set as outlet of the piston-chamber pumping instrument, and intensive shearing provided the shift of the droplet sizes to the smaller-size side of the distribution. Their distributions were wider and of Gaussian type. Two models were proposed and used to fit the refinement evolution and the width of distributions respectively.

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The nonlinear interactions between a fundamental instability mode and both its harmonics and the changing mean flow are studied using the weakly nonlinear stability theory of Stuart and Watson, and numerical solutions of coupled nonlinear partial differential equations. The first part of this work focuses on incompressible cold (or isothermal; constant temperature throughout) mixing layers, and for these, the first and second Landau constants are calculated as functions of wavenumber and Reynolds number. It is found that the dominant contribution to the Landau constants arises from the mean flow changes and not from the higher harmonics. In order to establish the range of validity of the weakly nonlinear theory, the weakly nonlinear and numerical solutions are compared and the limitation of each is discussed. At small amplitudes and at low-to-moderate Reynolds numbers, the two results compare well in describing the saturation of the fundamental, the distortion of the mean flow, and the initial stages of vorticity roll-up. At larger amplitudes, the interaction between the fundamental, second harmonic, and the mean flow is strongly nonlinear and the numerical solution predicts flow oscillations, whereas the weakly nonlinear theory yields saturation. Beyond the region of exponential growth, the instability waves evolve into a periodic array of vortices. In the second part of this work, the weakly nonlinear theory is extended to heated (or nonisothermal mean temperature distribution) subsonic round jets where quadratic and cubic nonlinear interactions are present, and the Landau constants also depend on jet temperature ratio, Mach number and azimuthal mode number. Under exponential growth and nonlinear saturation, it is found that heating and compressibility suppress the growth of instability waves, that the first azimuthal mode is the dominant instability mode, and that the weakly nonlinear solution describes the early stages of the roll-up of an axisymmetric shear layer. The receptivity of a typical jet flow to pulse type input disturbances is also studied by solving the initial value problem and then examining the behavior of the long-time solution. The excitation produces a wave packet which consists of a few oscillations and is convected downstream by the mean flow. The magnitude of the disturbance in the jet depends on the location of the excitation and there is an optimum position at which little energy input will produce large perturbations. It is found that in order to generate the largest perturbations at any point in the jet, the disturbance should be deposited into the flow at a point where the phase velocity of the most amplified wave equals the fluid velocity (of the base flow).

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Abstract not available