Extensional and shear rheology of dilute particle suspensions in viscoelastic liquids

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Abstract
Particle suspensions in viscoelastic or polymeric liquids undergo uniaxial extensional and/ or simple shear flows in several industrial and manufacturing processes such as hydraulic fracturing, extrusion molding, or fiber spinning. The resulting interaction of particles and polymers can lead to drastic changes in the suspension rheology, ultimately impacting the process efficiency. This thesis characterizes the fundamental mechanisms of particle-polymer interactions within the two flows mentioned above. It develops methods to study the flows of particle-filled viscoelastic fluids and evaluate the rheology of a dilute suspension in any weakly non-Newtonian fluid. In a uniaxial extensional flow, spherical particles and polymers interact to either increase or decrease the suspension stress due to the regions of highly stretched or collapsed polymers (relative to the polymers undisturbed by the velocity perturbations due to the particle), respectively, in the fluid around the particles. If the polymer relaxation time is large, as is often the case in applications, the polymer collapse happens more rapidly and persists for long times. The magnitude of reduction in suspension stress increases with the polymer relaxation time, the imposed extensional rate, and particle concentration. Therefore, adding only a small amount of particles to a viscoelastic fluid can reduce its extensional viscosity and improve the efficiency of the industrial process. Fibers are added to impart mechanical, electrical, or thermal anisotropy to the final cured product. In a Newtonian fluid, the fibers rotate in degenerate periodic orbits dependent on their initial orientations, making it challenging to obtain aligned particles necessary for obtaining an anisotropic material. Viscoelasticity can, however, break this degeneracy and allow better particle alignment. A theory is developed for slender prolate spheroids rotating in a simple shear flow of low concentration polymeric solution. It is the first theoretical prediction of a wide range of particle orientation behaviors observed in the experiments. Large aspect ratio particles rotating in fluids with a small polymer relaxation time migrate towards a specific small periodic orbit close to the vorticity axis. A stable orientation close to the imposed simple shear flow's flow direction is obtained for a large polymer relaxation time. The theoretical findings lead to a phase diagram of different particle orientation behavior depending on the fluid properties and particle aspect ratio. This can be instrumental in guiding the right choice of parameters in future experiments and in applications to obtain the desired anisotropy. One of the methods used to investigate the extensional rheology at low polymer concentrations is generalized to encompass the characterization of the rheology of any weakly non-Newtonian fluid. It is foreseen that this computationally inexpensive semi-analytical method can be used to guide the design of new fluids for achieving desired rheological properties. The second method is a sophisticated numerical tool that solves the flow of fully viscoelastic fluids around a prolate spheroidal particle, thus covering a range of shapes from a sphere to high aspect ratio fiber in an unbounded fluid. It helps test slender body theories, study a range of linear flows of viscoelastic fluids around an isolated particle and determine various rheologies of dilute particle suspensions.
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376 pages
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2022-12
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Koch, Donald
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Desjardins, Olivier
Esmaily Moghadam, Mahdi
Hormozi, Sarah
Degree Discipline
Mechanical Engineering
Degree Name
Ph. D., Mechanical Engineering
Degree Level
Doctor of Philosophy
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Government Document
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Attribution 4.0 International
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dissertation or thesis
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