The mixing of powders and liquids is a process ubiquitous to many industrial, research and household applications, from the production of foodstuffs, pharmaceutical and cosmetic products to the preparation of hot drinks or cement. The final mixed state of powders and liquids can be broadly split into two distinct regimes identified respectively as having low- and high volume fraction, ∅. Low-∅ systems are typified by flowing suspensions whereas samples prepared with high-∅, beyond some threshold value, produce solid agglomerates which are unable to flow. These two regimes are the focus of two separate scientific disciplines; suspension rheology and granulation. Within the field of suspension rheology there has been recent advances in the understanding of a phenomena known as shear thickening, which describes the increase in a suspension's viscosity with increasing applied stress. In this thesis we aim to unify the phenomena of shear thickening and granulation within this new theoretical framework. We study shear thickening and granulation using a well characterised model system developed for this purpose, comprising polydisperse glass particles with a mean diameter of ≃ 7 μm and a glycerol-water mixture (90:10 %vol). We measured the rheological behaviour as a function of applied stress, σ, of suspensions at various volume fractions. We observed shear thickening behaviour, with divergences in the low-stress viscosity, η1(∅), and the high-stress viscosity, η2(∅), at ∅RCP = 0:662 and ∅m = 0:572 respectively. These divergences mark the transition between continuous shear thickening, discontinuous shear thickening and a state in which flow is not possible, with increasing volume fraction. Using a recently developed theory of shear thickening (Wyart and Cates, 2014), we were able to fit our rheological data quantitatively. The WC theory predicts a stress-dependent crossover in the fraction of contacts which are frictional in nature, following a stretched exponential function. In order to improve numerical agreement between our data and the model, we developed a method taking into account the volume-weighted contribution of particle sizes in our polydisperse system. Bulk mixing of the same model system in a custom-built high-shear mixer also exhibited three different mixing regimes with the change in behaviour coinciding with the location of the viscosity divergences, ∅m and ∅RCP, measured in the rheology experiments. For ∅ < ∅m suspensions are formed at both high and low stress; for ∅ ≥ ∅RCP granules are formed at all stresses; for ∅m ≤ ∅ < ∅RCP transient granules are formed, which are solid at high stresses, but can relax to a flowing suspension state at low stress. This transient behaviour is reversible with the application of high stress. This coincidence of viscosity divergence in the rheology measurements and mixing behaviour change in the high-shear mixing strongly suggests that the two phenomena are related. Thus we used the stress-dependent jamming volume fraction, ∅J(σ), predicted by the WC theory, to define the transition between the formation of suspensions and granules. We were able to calculate a quantitative phase diagram, with which the regions of the ∅-σ phase space in which granules or suspensions are formed can be easily identified, in agreement with our high-shear mixer data. Thus, using small-scale rheological measurements, requiring relatively small volumes of sample, we are able to define the parameter space in which granules can be prepared, thus eliminating the need for trial and error granulation experiments in order to define this space. We measured the volume-weighted mean granule size as a function of ∅ in the range ∅m → ∅ ≃ 0:85. Based on our observations of granule structure and measurements of granule size distributions, we modelled the granules as an ensemble of core-shell agglomerates with a log-normal size distribution. The packing in the granule cores was assumed to be ∅J(σ ), i.e. ∅m at high stress and ∅RCP at low stress. Appealing to conservation of mass arguments, our model predicts that the mean granule size decreases with increasing volume fraction and stress, in quantitative agreement with experimental data.

Abstract In order to improve the optimisation of mineral processing operations the rheological properties of slurries must be determined as accurately as possible under the conditions that closely resemble actual site conditions. The rheology of particles suspended in Newtonian fluids is well documented. However, the rheology of particles in non-Newtonian fluids has not been the subject of much investigation till now. The work conducted here attempts to fill this gap in knowledge. The rheological properties of slurries are heavily dependent on the solids concentrations and particle-solid interaction. At low solids concentrations, constant viscosity and Newtonian behaviour is observed, but as solids concentration increases the rheological behaviour becomes increasingly complex and non-Newtonian with viscosity becoming dependent on the shear rate. The nature of the non-Newtonian behaviour depends on the solid concentration, particle shape, particle size, particle size distribution and the suspending liquid rheological properties. The suspension/slurry may develop a yield stress and become time dependent in nature as structures develop within the fluid at higher solids concentrations. This study however, is primarily focused on the measurement of the rheological properties, where it is assumed that the fluid will be fully sheared and that the rheological properties will be unlikely to change with time. Shear thickening behaviour of slurries was the focus of this work. The aim was to investigate the slurry concentration region where shear thickening occurs. The first objective of the project was to develop a fluid analogue which will have similar rheological behaviour to that of concentrated tailings from gold mines so that it can be used as a test material to simulate the flow behaviour of the tailings in a pipe. The second objective of this project was to enable the prediction of flow behaviour in the pipe loop under certain conditions using the fluid analogue for slurry from Sunrise dam. In order to achieve the objectives, experiments were carried out to obtain a fluid analogue of a shear thickening slurry. CSL 500 and SR 200 rheometers were used for the characterisation of different fluid analogues and shear thickening mineral slurries. Malvern Sizer, model: mastersizerX v1.1, was used to obtain particle size distributions. A mini pipe loop system, located in the laboratory of the Rheology and Materials Processing Centre (RMPC) was used to get pipe line flow data for comparison with the rheometer data. A few fluid analogues with different suspending medium and different concentrations of glass spheres was tested before finally using, 48 vol% glass spheres in 1.8 wt% CMC solution as a fluid analogue for the mineral tailings obtained from Sunrise dam, WA. For comparison between the pipe line and rheometer data, all pipe line data (in the form of 8V/D) were converted to rheometer data (in the form of du/dr) using the Robinowitsch-Mooney equation. The above comparison indicated that it is possible to produce fluid analogue to simulate the flow behaviour of Sunrise dam slurry using a shear thinning suspending medium with high concentration of glass particles. Shear thickening flow behaviour was clearly observed in the rheometer while it was less predominant in a pipe line flow.

Transport properties of concentrated suspensions are of interest to many industries. Mineral slurries at higher solids concentrations have shown some rheologically interesting characteristics such as shear thickening, the increase of viscosity of a multi-phase mixture with increasing shear rate. The general literature on the rheology of suspensions records the presence of yield stresses, shear thinning and normal stress differences. Little is said specifically about shear thickening behaviour except for colloidal suspensions. The aim of this study is to examine the behaviour of coarse shear thickening suspensions and determine the causes of this phenomenon. The study intended to achieve the following objectives to; develop the appropriate techniques for rheometric studies of shear thickening suspensions; investigate the nature of particle-fluid interaction; develop a model of shear thickening behaviour as it occurs in non-colloidal suspensions and to develop a method of applying the rheology results to flows and flow geometries of practical relevance. The effects of wall slip dominate much of the literature of shear thickening materials. To investigate this aspect a significant portion of the experimental work examined the effect of shear thickening on torsional flow. The rheogram produced from parallel plate rheometry was reassessed as a non-controlled flow and a rheology model dependant analysis demonstrated that the effects of slip are considerably more problematic for shear thickening suspensions, particularly as wall slip is an increasing function of shear stress. As a consequence of the rheometric method described above it was observed that the rate of change of the first normal stress difference, N1, with shear rate changes as shear thickening commences for non-colloidal suspensions. N1 is initially negative and is increasingly negative at low shear rates. Additional rheometric analysis examined the transient effects in the behaviour of a non-colloidal shear thickening suspension. By employing large angle oscillating strain tests the strain required to initiate a shear thickening response was determined. Coherent back scattering of laser light experiments were able to show the change in orientation of the particles with respect to its rotation around the vorticity axis. After a viscosity minimum was reached the orientation became more random as particle rotation and lamina disruption occurred. This was considered to be the cause of the measured shear thickening. A model of shear thickening in concentrated, non-colloidal suspensions of non-spherical particles was developed. Based on hydrodynamic interaction in the Stokes flow regime, the flow of interstitial fluid subjected the adjacent particles to lubricating and Couette type forces, acting as a couple. When a series of force balances on a particle contained between two moving laminae are conducted as a time sequence, the particle orientation and motion can be observed. The model has qualitative agreement with several aspects of the experimentally observed behaviour of shear thickening suspensions, such as viscosity change with shear rate and concentration, and the first normal stress difference increasing with shear rate. Pipe line flow experiments were conducted on the model suspension. Particle settling produces unusual patterns in shear thickening suspensions, with an annulus of delayed settling near the wall.

A particulate suspension under shear is a classic example of a system driven out of equilibrium. While it is possible to predict the equilibrium phase behaviour of a quiescent suspension, linking microscopic details to bulk properties under flow remains an open challenge. Our current understanding of sheared suspensions is restricted to two disparate regimes, the colloidal regime, for particle sizes d < 1 μm and the granular regime, for d > 50 μm. The physics of the industrially-relevant intermediate size regime, 1 μm ≲ d ≲ 50 μm, is unclear and has not been explored previously. In this thesis, we use conventional rheometry on a range of model spheres to develop the foundations of a predictive understanding of suspension flow across the entire size spectrum. In the first part of the thesis, we show that in repulsive particulate systems the rheology is characterised by two viscosity "branches" diverging at different volume fractions φRCP and φm, which represent states of flow with lubricated (frictionless) and frictional interactions between particles. In the intermediate size regime, there is a transition between these two branches above a critical onset stress σ* which manifests as shear thickening. This σ* is related to a barrier (invariably due to the charge or steric stabilisation) keeping particle surfaces apart. Our data are quantitatively fit by the Wyart and Cates theory for frictional thickening [1] if we assume that probability distribution of forces in the system is similar to in dry granular media. The onset stress for shear thickening is found to decrease with the inverse square of the particle size σ* / d ̄ 2 for diverse systems. We show that it is the competition between the scaling of σ*(d) and the size dependence of the entropic stress scale (~ d ̄ 3) that controls the crossover from colloidal to granular rheology with increasing size. Granular systems are "always shear thickened" under typical experimental conditions, while colloidal systems are always in a frictionless state. In the second part of the thesis, we explore the validity of the frictional framework for shear thickening. Although it quantitatively predicts our steady-state rheology, the frictional framework contradicts traditional fluid-mechanical thinking and has yet to be rigorously tested experimentally. In fact, there is a large body of literature that attributes thickening to purely hydrodynamic effects. Using dimensional analysis and simple physical arguments we examine possible physical origins for thickening and show that previously-proposed mechanisms can be subdivided into three types: two-particle hydrodynamic thickening, many-particle hydrodynamic thickening ("hydroclusters") and frictional-contact driven thickening. Many of these mechanisms can are inconsistent with the experimental two-branch phenomenology and can be disregarded. We further narrow down possible causes of thickening using the technique of flow reversal, which disentangles the relative contributions of contact and hydrodynamic forces to the viscosity. Consistent with recent simulations [2] and theory [1], we find that in each case thickening is dominated by the formation of frictional contacts and that hydrodynamic thickening, if present, is subdominant.

Shear thickening fluids have the potential to improve the effectiveness of fabric materials in body armor applications as they have shown to increase the puncture and ballistic resistance of Kevlar fabrics. However, the effect of using STFs with natural fabrics such as flax has never been studied. The rheology of STFs at varying concentrations of nanosilica dispersed in polyethylene glycol PEG was studied at different temperatures and it was found that the STFs behave as a non-Newtonian fluid in response to changes in shear rate. In this study the effectiveness on the puncture and ballistic resistance of impregnating flax fabric with STF of nanosilica in PEG were investigated. The effect of hybridization of flax and Kevlar was also investigated. The puncture and ballistic resistance of the samples treated with STFs was found to increase significantly and can be controlled by STF concentration.

Master of Science / Department of Mechanical and Nuclear Engineering / B. Terry Beck / The objective of this project was to first evaluate the feasibility of developing a viscous damping device that used a Non-Newtonian Shear Thickening Fluid (STF) and incorporating it as a door latch into an existing commercial dryer unit. The device would keep the door closed during sudden large magnitude impact loads while still allowing the door to open normally when force is applied gradually at the door handle. The first phase of the project involved performing background research on the subject and performing preliminary analysis in order to determine if the concept was feasible enough to be worth constructing a physical prototype. This preliminary analysis consisted of a literature review of existing damping mechanisms and shear thickening fluids, rheometer testing of shear thickening suspensions to obtain viscosity data, and performing numerical simulations to determine if a damper that fit the size requirements could produce enough resistance force. The focus for the second phase of the project was to demonstrate a proof of concept in the form of a working model prototype. This prototype did not need be of identical shape and proportions as the finalized design, but would be developed to facilitate experimental testing and evaluation of performance under the desired operating conditions. It was also necessary to design and construct the test setup for the dynamic testing of the dryer door opening so that the opening displacement as well as the force applied to the door could be recorded as a function of time. The final phase of the project consisted of improving upon the original prototype in order to prove the validity of a viscous latch beyond the proof of concept phase in a form closer to what is desired for the commercial product. This required reducing the physical size of the new prototype latch so as to fit within the space available in a particular dryer, incorporate a one-way ratcheting device into the latch to allow unrestricted closing of the door, and increase the operational temperature range of the damper.

No description available.

A suspension is a fully saturated mixture of discrete solid particles and interstitial liquid. Examples of suspensions include pastes, slurries, cement, food-spreads, drilling fluids and some geophysical flows. The present work focusses on granular (as opposed to colloidal) suspensions, which we define as those for which the thermal motion of the solid particles is negligible. Despite such ubiquity in industry and nature, our understanding of the mechanical properties of suspensions lags behind that of their constituent solid and liquids. In this thesis, the discrete element method is used to simulate suspension flow in shear, capillary and constriction geometries, mapping and characterising the fundamental flow, or rheological, regimes. As a starting point (Chapter 2), we consider an established regime map for dry granular materials, appropriate for flows of sand, grains and dry debris. Taking guidance from shear flow simulations that consider the lubricating effect of an interstitial liquid, we recast the regime map for a general suspension, elucidating flows comparable to the dry material or to a viscous liquid, dependent on the shear rate, liquid viscosity and particle stiffness. We give an account of the microstructural traits associated with each regime. Motivated by recent groundbreaking theoretical, computational and experimental work, we incorporate the emerging picture of frictional shear thickening into our regime map (Chapter 3). Our shear flow simulations capture the shear thickening behaviour and demonstrate that it may, in principle, occur in any of the identified flow regimes. Our simulations of time-dependent shear flows (Chapter 4), specifically flow reversal, provide a detailed micro-mechanical explanation of a longstanding and previously unexplained experimental finding, guiding future experimentalists in decomposing the particle and liquid contributions to the viscosity of any suspension. Indeed, the findings have already been exploited in the devising of an experimental protocol that has successfully proven the dominance of particle contacts in driving shear thickening. We next consider suspension flow in a microchannel (Chapter 5), finding that the identified shear flow regimes are locally applicable to flows in complex geometries under inhomogeneous stress conditions only when the local mean shear rate exceeds temporal velocity fluctuations. A more comprehensive description is therefore required to fully characterise the flow behaviour in this geometry. Finally (Chapter 6), we simulate pressure driven suspension flow through a constriction geometry, observing highly inhomogeneous stress distributions and velocity profiles. The roles of particle and fluid properties are considered in the context of an industrial paste extrusion process.

Cette thèse de doctorat a été financée par l’entreprise SIKA spécialisée dans les matériaux de construction. Les trois chapitres de cette thèse correspondent à la tentative de résolution de trois problématiques d’origine industrielle. Dans le premier chapitre, nous avons étudié l’effet de la concentration en particules sur les propriétés d’écoulement de fluides complexes rhéofluidifiants ou rhéoépaississants et démontré l’origine microscopique de cet effet. Dans le second chapitre, nous avons étudié la floculation de particules colloïdales sous faibles perturbations et mis en évidence l’existence, au cours de la reconstruction, d’un maximum du module élastique. Enfin le troisième chapitre est l’étude d’un diagramme de phase de jet de suspensions concentrées. En régime dilué et semi-dilué, les résultats sont conformes à ceux de la bibliographie, en revanche nous avons étudié un nouveau régime à très haute fraction volumique où le jet, instable, se met à osciller. Nous avons montré que ces oscillations étaient dues au rhéoépaississement de la suspension. / This thesis has been done in collaboration with the company SIKA, one of the leader if the construction industry. This thesis report is organized in three chapters where each of them tries to answer a problem coming from industrial processes. In the first chapter, we studied the impact of particles concentration on the flowing properties of complex fluids such as shear-thinning and shear-thickening fluids. We demonstrated the importance of local contacts between particles to explain the evolution of the viscosity with the volume fraction. In the second chapter, we studied the aggregation of colloidal attractive suspensions under small perturbations and proved the existence of a maximum of elastic modulus during the rebuilding of the structure. Finally, the third chapter is a study of a phase diagram of a concentrated suspension jets. In the diluted and semi-diluted regimes, we found results in agreement with the bibliography, meanwhile at very high concentration, we studied a new regime where the jet, unstable, is oscillating. We showed those oscillations can be explained by the shear-thickening behaviour of the suspensions at those high concentrations.

Les suspensions de grains rigides dans un fluide constituent une classe de fluides complexes présentant une rhéologie riche. Même dans les cas simples où le fluide est Newtonien, et les grains sphériques, non Browniens et non colloïdaux, les comportements macroscopiques observés restent mal compris, en particulier dans le cas de suspensions concentrées. Dans ces matériaux, la complexité de la dynamique provient de l'équilibre subtil qui se met en place entre les interactions de nature hydrodynamiques portées par le fluide interstitiel et les forces de contact entre les grains. Dans ce travail, nous abordons ces questions sous l'angle de la simulation numérique discrète, dans le cadre du cisaillement simple de suspensions concentrées 2D. Nous modélisons les efforts hydrodynamiques par des interactions de lubrification de paires, couplées à un modèle de contact éventuellement frottant. L'inertie des grains n'est pas négligée. Nous accédons à tous les coefficients du tenseur des contraintes, ce qui permet de mesurer pression, contrainte de cisaillement, et différence des contraintes normales, ainsi que les viscosités associées. L'étude du cisaillement à volume constant nous permet de mettre en évidence l'existence d'une transition de rhéo-épaississement entre un régime visqueuse à bas taux de cisaillement (contrainte proportionnelle au taux de cisaillement) et un régime inertiel à haut taux de cisaillement (contrainte proportionnelle au carré du taux de cisaillement), selon que la contrainte soit dominée par les interactions de lubrification ou par l'inertie des grains. Le taux de cisaillement de transition mesuré est compatible avec un argument d'échelle pour la contrainte, tenant compte de sa divergence avec la fraction volumique. Des simulations du cisaillement à pression constante nous permettent ensuite d'explorer le comportement de suspensions très concentrées (jusqu'à 1% de la fraction volumique de blocage théorique) dans leur domaine d'écoulement visqueux. Nous montrons que la rhéologie du mélange peut se décrire sous la forme d'une loi d'écoulement dépendante du seul nombre visqueux, construit comme le rapport entre un temps caractéristique de réarrangement local des grains sous l'effet des forces visqueuses et un temps typique de convection imposé par l'écoulement. Cette description nous permet de caractériser précisément la divergence de la contrainte avec la concentration en particules. Enfin, nous mesurons la microstructure stationnaire développée dans l'écoulement. Nous mettons en évidence une anisotropie importante des contacts générés, et discutons l'évolution de cette distribution avec la concentration du mélange / Suspensions of rigid grains in a fluid constitute a class of complex fluids that present a rich rheology. Even simpler cases of non-Brownian, non-colloidal spherical grains suspended in a Newtonian fluid feature macroscopic behaviours that are still not completely understood, especially when the concentration of particles is high. In these materials, the complexity of the dynamic is the result of the subtle balance that occurs between hydrodynamic interactions mediated by the interstitial fluid, and contact forces between grains. In this work, we tackle those questions from the point of view of discrete numerical simulations, in the context of the simple shear of 2D concentrated suspensions. Hydrodynamic interactions are modelled by pair lubrication, coupled with a possibly frictional contact law. Grains inertia is not neglected. We have access to the whole stress tensor, allowing the measure of pressure, shear stress, and normal stress difference, as well as their associated viscosities. The study of constant volume simple shear shows the existence of a shear-thickening transition between a viscous regime at low shear rate (stress proportional to the shear rate) and an inertial regime at high shear rate (stress proportional to the shear rate squared), depending on whether the stress is dominated by lubrication interactions or grains inertia. The position of the measured transition shear rate is consistent with a scaling argument for the stress that takes its divergence with concentration into account. Constant pressure simple shear simulations then let us explore the behaviour of very concentrated suspensions (up to 1% to the theoretical jamming fraction) in their viscous flow domain. We show that the rheology of the mix can then be described by a flow law that is only function of the viscous number, constructed as the ratio of a typical time for the local rearrangement of grains subjected to viscous forces, and a convection time consistent with the imposed flow. This allows a precise characterization of the divergence of stress with particles concentration. At last, we measure the stationary microstructure that develops within the flow. We show an important anisotropy of contacts, and discuss the evolution of this distribution with the concentration of the suspension