Browsing by Subject "Hydrodynamics"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Chemical and Hydrodynamic Effects in Polymer-Clay Flocculation: Anisotropic particulate size and surface morphology effects in varied and controlled hydrodynamic fields
    (2017-12) Wilkinson, Nikolas
    Polymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. Properties including ionic strength and pH affect both the individual particulate aggregates themselves, as well as the polymer – particle flocculation event. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles using traditional jar tests. The final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Additionally, the clay’s aggregate morphology is a more direct control parameter of optimal polymer dose and final turbidity (turbidity after 5 min sedimentation) than zeta potential for aqueous bentonite systems. Flocculation performance is the same when bentonite aggregate morphology is the same, regardless of a change in zeta potential. Likewise, when bentonite aggregate morphology changes, flocculation performance also changes, regardless of the identical zeta potential. Therefore, initial clay aggregate morphology controls the extent of polymer adsorption and optimal polymer dose, while initial clay aggregate size controls the internal floc structure. While traditional jar tests offer the advantages of experimental simplicity, speed, and mimic treatment geometries, there is limited homogeneity and control over hydrodynamics within the system. Taylor-Couette cells offer a much higher degree of hydrodynamic control and have been shown to improve several industrial processes due to the wide variety of hydrodynamic flow states accessible. Traditional designs, however, limit the ability to introduce new fluids into the annulus during device operation due to geometric confinement and complexity. As a key part of this thesis effort, a co- and counter-rotating Taylor-Couette cell with radial fluid injection has been constructed. The new inner cylinder design does not modify the critical Re for flow instabilities and can precisely inject a desired mass at a desired flow rate. Using the newly designed, modified Taylor-Couette cell, axial mass transport behavior is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the estimated dispersion coefficient was found to increase with increasing Re, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A new dimensionless stability criterion, the ratio of injection to diffusion timescales, was utilized to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, Re. Overall, this thesis examines chemical and hydrodynamic effects in polymer flocculation with natural clays, and shows the importance of initial contaminant properties on flocculation performance. The initial contaminant properties affect both flocculation efficiency and resultant floc structure and are often not considered at treatment plants. Consideration of these properties potentially can improve process predictive capabilities, which improves process performance.
  • Thumbnail Image
    Item
    The effects of fluid flow on the spatial density, distribution, and metabolism of larval Glossosoma
    (2013-05) Morris, Mark William Lehnardt
    The focus of this research was the mechanistic relationship between fluid flow, spatial density, distribution, and metabolism of stream-dwelling insect larvae of the caddisfly genus Glossosoma (Glossosomatidae: Trichoptera). Glossosoma are ecologically important for many reasons, including that they are dominant grazers in lotic food webs, are capable of suppressing stream periphyton, and act as an indicator of stream health. A description is herein presented of fluid flow and stream bathymetry environments where Glossosoma are often present. Predictive relationships for Glossosoma spatial density are proposed from local fluid flow and channel bathymetry variables. The research was conducted through a series of four separate studies. First, habitat was quantified for larval Glossosoma in three coastal mountain streams in northern California. Applying dimensional analysis, a functional relationship was developed for predicting larval abundance. Variogram analysis of Glossosoma spatial density and bed topography revealed overlap in the separation distance above which point measurements were statistically independent. Second, field measurements were conducted in Valley Creek, Minnesota and data were compared with the measurements in the coastal mountain streams. Third, a computational model was employed to estimate high resolution fluid flow variables along a riffle in Valley Creek. Simulation results were verified and implemented in a predictive model for Glossosoma abundance. Fourth, a laboratory study of Glossosoma metabolism under varying flow conditions revealed generally increasing oxygen consumption with increasing fluid flow velocities. The proposed research will be instrumental for predicting not only how Glossosoma respond to changes in fluid flow and stream bathymetry conditions, but also how these variables influence larval spatial density, distribution, and behavior in lotic environments.
  • Thumbnail Image
    Item
    Hydrodynamics of strongly coupled non-conformal fluids from gauge/gravity duality.
    (2009-08) Springer, Greggory Todd
    The subject of relativistic hydrodynamics is explored using the tools of gauge/gravity duality. A brief literature review of AdS/CFT and gauge/gravity duality is presented first. This is followed by a pedagogical introduction to the use of these methods in determining hydrodynamic dispersion relations, w(q), of perturbations in a strongly coupled fluid. Shear and sound mode perturbations are examined in a special class of gravity duals: those where the matter supporting the metric is scalar in nature. Analytical solutions (to order q4 and q3 respectively) for the shear and sound mode dispersion relations are presented for a subset of these backgrounds. The work presented here is based on previous publications by the same author [1], [2], and [3], though some previously unpublished results are also included. In particular, the subleading term in the shear mode dispersion relation is analyzed using the AdS/CFT correspondence without any reference to the black hole membrane paradigm.
  • Thumbnail Image
    Item
    Polymer Solutions in Complex Flows: Fibrils, Filaments, and Flocs
    (2020-08) Metaxas, Athena
    The behavior of polymers in solution under complex physicochemical and hydrodynamic flow fields is of interest to a variety of industrial processes, such as polymer processing and water treatment. In this thesis, two main areas are presented: (1) self-association of polymer chains in flow, resulting in the formation of fibrils and filaments, and (2) association of polymer chains with suspended particulate, resulting in the formation of flocs. In the first area, extensional properties of methylcellulose (MC) solutions were characterized using millimeter scale capillary thinning and micrometer scale filament stretching methods. The addition of NaCl to MC solutions results in self-assembly of a fraction of the MC chains into MC fibrils, which imparts elastic characteristics to the solution. Capillary Breakup Extensional Rheometry (CaBER) studies demonstrate the extensional relaxation time and extensional viscosity increased with increasing MC concentration in the presence of salt. Likewise, microfluidic filament stretching studies demonstrate the extensional viscosity increased with increasing NaCl concentration. By reducing the characteristic length scale of the thinning filament, the microfluidic platform enabled new measurements extensional properties for low molecular weight and low viscosity MC solutions. In the second area, the assembly of charged polymers, or polyelectrolytes, with bentonite clay into flocs was studied in complex flow fields using macroscale Taylor-Couette (TC) flows. A custom-built TC cell allowed for injection of the polyelectrolyte solution into the particle-laden flow to investigate in-situ floc nucleation and growth in varied hydrodynamic flow states. Faster floc growth rates and decreased 2-D perimeter-based fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and shear rounding of the flocs, respectively. Additionally, the effects of ionic strength and polyelectrolyte molecular weight on flocculation in the TC cell were investigated. Smaller flocs were formed with increasing ionic strength, due to the role of charge screening on the initial bentonite aggregate size and polyelectrolyte chain persistence length and conformation in solution. Overall, this thesis seeks to provide additional understanding of how polymers assemble in solution under a variety of physicochemical conditions and flow, which can inform predictive processing capabilities and performance.
  • Thumbnail Image
    Item
    Relativistic Fluids of Topological Defects
    (2015-09) Schubring, Daniel
    A number of papers on the topic of string fluids written by Vitaly Vanchurin and myself are reviewed. A network of Nambu-Goto strings is coarse-grained and the equations for a generalized fluid are derived. Besides the symmetric energy-momentum tensor, the fluid also has a conserved antisymmetric tensor $F$ related to the topological flux of strings. This $F$ tensor obeys the homogeneous Maxwell equations, and there is a topological constraint similar to Gauss's law for magnetism. The fluid is isentropic and pressureless and foliated by two-dimensional submanifolds which can be considered to be worldsheets of macroscopic strings. The macroscopic strings are shown to obey the known equations of motion of a wiggly string. The fluid can be generalized to have pressure and be foliated by arbitrary current carrying strings by introducing a natural variational principle. An action is constructed as a functional of three scalar fields which can be identified as the Lagrangian coordinates of the fluid. This same variational principle for a specific choice of functional is shown to lead to the equations of magnetohydrodynamics, in which the $F$ tensor above is indeed the electromagnetic tensor. Furthermore a minor modification in the fields varied leads to the equations for a model of vortices in a superfluid. The effect of dissipation can be introduced by allowing the $F$ tensor and energy-momentum tensor to depart from their equilibrium forms. The condition that entropy must increase restricts the form of the non-equilibrium components of these tensors, and leads to the analogue of the Navier-Stokes equations for a string fluid. Besides terms involving viscosity there are additional terms dependent on the curvature of the lines of flux. In the case of magnetohydrodynamics these additional terms are shown to be equivalent to Ohm's law and the thermoelectric Nernst effect. The condition that the non-equilibrium terms vanish is used to derive conditions for hydrostatic equilibrium that may be useful in astrophysical situations.
  • Thumbnail Image
    Item
    Stratification stability of tropical lakes and their responses to climatic changes: Lake Towuti (Indonesia)
    (2023-01) Pu, Tongyao
    Tropical lakes have different physical dynamics. They can be permanently stratified by temperature gradients alone (thermogenic meromixis). This project aims to investigate the strength and dynamics of thermogenic meromixis in tropical lakes. To address this problem, physical and chemical dynamics of tropical Lake Towuti are simulated. The simulations reveal that Lake Towuti may be oligomictic and there is a possibility that whole water column mixing happened as recently as 2008. A weak mixing event lasting a few weeks during the dry season would be consistent with the observed chemical profiles of oxygen, hydrogen sulfide, and reduced dissolved iron. Findings suggest that, under the future climate characterized by warmer air temperatures, Lake Towuti is likely to be more stable. Stronger stability and isolation of monimolimnion water would lead to further accumulation of dissolved iron.