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The concentration of fine particle suspensions is a crucial step in many industrial processes, two major processes that depend on this are the disposal of mine tailings as highly concentrated slurries, and the wet casting of ceramic components from highly concentrated suspensions. The thickening and filtration operations in these processes are still not completely understood. The successful design and operation consolidation equipment must be based on the properties of the target suspension. The quantitative characterisation of suspensions in settling and compression was the prime objective of this thesis. (For complete abstract open document)

Thesis (Ph. D.)--University of Melbourne, Dept. of Chemical Engineering, 1997. / Typescript. Includes bibliographical references (leaves 197-209).

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The behavior of bimodal suspensions of oblate spheroids undergoing simple shearing flow has been described by analyzing the frequency spectra of orientation-dependent macroscopic properties. In particular, the frequency spectra of rheo-optical transients in turbidity and angular light scattering obtained experimentally from mono- and bimodal suspensions of human and frog erythrocytes showed peaks corresponding to the dominant frequencies of the particles in the flow. The method can, in principle, be applied to multimodal dispersions to obtain information on particle geometry. / The effect of high polydispersity on the rheo-optical transients of sheared suspensions have been studied. The time-dependent behavior of such systems is neither determined by the period of rotation defined by the mean axis ratio nor by the mean period of rotation amongst particles, but by the most probable period of rotation (i.e. the value corresponding to the maximum in the distribution of periods of rotations). Rheo-optical transients in polydisperse kaolin (clay) suspensions have been experimentally obtained. Here the oscillations, in contrast to the slightly polydisperse suspensions studied previously, are highly damped. Frequency spectra obtained from these experiments have peaks near 2/T(,m) , where T(,m) is the most probable period in the ensemble. / Finally, the influence of the rotary Brownian motion on the rheo-optical transients of sheared spheroidal suspensions is considered by using simulation procedures such as those employed previously to analyze rheological properties and memory loss. The rotary Brownian motion induced two effects: damping of oscillations and a shift in the extrema of the oscillations resulting in variation in the apparent mean period of rotation. Experiments with human erythrocytes at low Brenner number confirmed such behavior. Also a system with strong rotary Brownian motion was observed for which the rheo-optical transients showed monotonic changes. / The observations made in this work contribute to a better understanding of the transient rheo-optical properties of flowing suspensions.

Une étude combinant expériences et analyses est menée afin de rationaliser la dynamique et la rhéologie des suspensions très concentrées de fibres rigides, non colloïdales dans un fluide newtonien. Des mesures rhéologiques couplées à des mesures de la microstructure sont réalisées à l’aide de plusieurs dispositifs expérimentaux permettant d’analyser différents types de géométries et d’écoulements. Des expériences de rhéologie standards (rhéologie à volume contrôlé), ainsi qu’une méthode de rhéologie non-conventionnelle (rhéologie à pression contrôlée) sont associées afin de mesurer la contrainte de cisaillement, la pression de la phase particulaire et la fraction volumique des suspensions très concentrées. Un autre dispositif expérimental a été conçu dans le but d’étudier la microstructure (distribution spatiale et distribution d’orientations) d’une suspension de fibres rigides dans un écoulement de Poiseuille oscillant. Alors que ce type d’écoulement est réversible pour un liquide newtonien, dans le cas d’une suspension concentrée, les interactions entre particules introduisent des changements irréversibles de microstructure. Cette microstructure est affectée et a un effet sur l’écoulement imposé, cette dépendance non-linéaire incluant les interactions hydrodynamiques. L’objectif de ces expériences est d’apporter un éclairage sur des effets tels que la rhéofluidification observée à fort taux de cisaillement et sur le démixage dû à la migration induite par cisaillement. / A combined work of experiments and data analyses is proposed to investigate the dynamics and rheology of highly concentrated suspensions of non-colloidal rigid rods in a Newtonian fluid. Detailed measurements of the rheology and the microstructure are made using a variety of experimental devices with different geometries and imposed flows. Standard rheology experiments (volume-controlled rheology), as well as a novel method of rheometry, are carried out to measure torques, particle pressures, and volume fractions at high concentration (pressure-controlled rheology). Another experiment has been designed and constructed to study the microstructure (spatial and orientation distribution) of a suspension of rigid rods in an oscillatory parabolic flow. Though the flow is reversible in these systems, the changes in the microstructure are irreversibile in the case of concentrated suspensions due to particle interactions. The microstructure is affected by, and has an effect, on the imposed flows; this non-linear dependency includes hydrodynamic interactions. The purpose of these experiments is to gain insight into phenomena such as apparent shear-thinning at high shear rates and demixing due to shear-induced migration.

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This thesis has explored the use of compliant mechanisms in vehicle suspension systems, specifically where a compliant mechanism acts as part of the wheel locating mechanism and as the energy storage element. A compliant mechanism has the potential of reducing part count, joints, and manufacturing and assembly costs of a suspension system. Fatigue failure has been found to be a limiting design constraint which competes with space and weight constraints. Controlling wheel motion in response to control forces has also been shown to be an important functional requirement for a compliant suspension system. Vehicle applications that are best suited for the use of compliant suspension systems are those that are low weight, have low energy storage requirements, and do not require precise vehicle handling characteristics. New compliant suspension concepts have been explored that support the wheel in 3-dimensions to minimize undesired wheel motions. These new concepts demonstrate increased stiffness and decreased stress due to control forces. Of these concepts, the compliant A-Arm proves to be the most promising candidate for future development. It has added advantages of lower space requirements, lower number of extra joints and rigid links, and simpler design for manufacture and assembly. The stiffness, stress, and kinematic characteristics of the compliant A-Arm configuration have been explored. This configuration has a non-linear force-deflection curve that is facilitated by the stress-stiffening effects of large deflections. A closed-form linear stiffness solution and a pseudo-rigid-body model has also been developed to aid in the initial design of the compliant A-Arm in a suspension system.

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