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Carpen, Ileana Cristina Brady John F. Brady John F. "Studies of suspension behavior : I. Instabilities of non-Brownian suspensions. II. Microrheology of colloidal suspensions /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-06022005-131439.
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Dorrell, Robert Michael. "Particulate Suspensions : The Mechanics of Suspension and Deposition." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525454.
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Brezas, Panagiotis Panos. "Time-domain optimal control for vehicle suspensions." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607986.
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Bennington, Chad Patrick Joseph. "Mixing pulp suspensions." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28622.
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Initiation and maintenance of motion within a pulp suspension is necessary for effective
mixing. This requires imposition of forces greater than the network strength and depends on suspension rheology once motion begins. As pulp suspensions display non-Newtonian and solid-like behaviour, studies were conducted using profiled rotors which imposed stress within the body of suspensions contained in cylindrical devices. A concentric
cylinder device capable of high torques (85 N-m) and high rotational speeds (524 rad/s) was built to study pulp suspension dynamic behaviour. Most work used a profiled rotor 0.1 m in diameter with baffled housings 0.13 and 0.22 m in diamter. The yield stress of low consistency pulp suspensions were measured with a Haake RV12 Ro-tovisco concentric cylinder viscometer. Semi-bleached kraft pulp was used throughout the study. Some tests were made with stone groundwood and thermomechanical pulps. Yield stress measurements were made for nylon and Spectra-900 fibre suspensions.
The yield stress of pulp suspensions, ty, have been measured and correlated with mass concentration (Cm) and volumetric concentration (Cv) over the range 0.4 ≤ Cm(%) ≤ 33. It was found that because of increasing gas content that correlations developed using the mass concentration were inaccurate above approximately 20% Cm. Correlations developed using the volumetric concentration were accurate over the full range tested. For a West-Coast semi-bleached kraft pulp, ty(Pa) = 1.40CV(%)²ֹ⁷².
Once rotor motion was initiated, pulp suspensions exhibited two distinct regimes of behaviour. The first was a tangential-cavity regime in which predominantly tangential motion grew to fill the chamber as shear rate increased. When motion reached the outer housing wall a flow transition occurred, likely triggered by flow interaction with the housing baffles. The subsequent post-transition regime was characterized by radial and axial flow that effectively mixed the suspension on both the macroscale and fibre-scale. The flow transition appeared to be what earlier workers reported as the onset of "fluidization".
During tangential-cavity flow, phase segregation occurred. Gas present in the suspension
collected around the rotor and reduced momentum transfer from the rotor to the suspension. This caused the torque for the pulp suspension to fall below that for water at the same rotational speed, and the cessation of flow development in the chamber. If sufficient momentum transfer was attained to initiate post-transition flow, the chamber contents became effectively mixed. The torque could still fall below that of water depending on the effective density of the suspension in the rotor vicinity.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
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Allred, Timothy Melvin. "Compliant Mechanism Suspensions." BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/434.
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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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Purnomo, Eko Hari. "Rheology of aging suspensions." Enschede : University of Twente [Host], 2008. http://doc.utwente.nl/59045.
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Cunha, Francisco Ricardo da. "Hydrodynamic dispersion in suspensions." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338138.
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Townsend, A. K. "The mechanics of suspensions." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1559911/.
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Suspension mechanics—the flow of a fluid with small fragments of solid material suspended in it—is an area of wide applicability in both industry and nature. Examples include the transport of silt in rivers, the manufacture of toothpaste, and inkjet printing where pigments remain solid within the ink. One widespread method to simulate these flows is Stokesian Dynamics, a truncated multipole expansion of the Stokes equations. It is computationally efficient while making a reasonable approximation to the hydrodynamic interactions between particles; however, all particles are identical spheres and the background matrix must be Newtonian. This project extends Stokesian Dynamics to include differently-sized spheres. This allows us to study a variety of previously inaccessible suspension problems. In many suspensions, e.g. toothpaste, the suspending fluid itself is non-Newtonian and exhibits viscoelastic properties. We have extended Stokesian Dynamics to incorporate a simple model of viscoelasticity by using the small spheres as 'beads' in bead--spring dumbbells. Different spring laws are then tested in shear, and their rheological behaviour is compared to continuum constitutive models. Next, we replicate experiments in which a large sphere is dropped through a suspension of neutrally buoyant smaller spheres undergoing oscillatory shear flow. We qualitatively replicate the principal experimental observation—that at the moment of shear reversal, the suspension microstructure hinders the falling; while at the instant of fastest shear, it enhances the falling. We propose a physical mechanism explaining the observations. Finally, we extend Stokesian Dynamics to properly implement interparticle frictional contact. Contact forces are a critical component of shear thickening in suspensions such as cornflour, yet are usually implemented in an ad hoc way, resulting in inaccurate predictions or high computational cost. The new method allows us to investigate contact models quickly and efficiently, and suggests an important factor in models of strongly shear-thickening fluids.
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Cortright, Emily Celia. "Microfluidics of DNA Suspensions." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1242236618.
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Burelbach, Jérôme. "Thermophoresis in colloidal suspensions." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274357.
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This dissertation examines the motion of colloids in a temperature gradient, a non-equilibrium phenomenon also known as thermophoresis. Chapter 1 gives an introduction to the existing applications and basic concepts of thermophoresis and outlines some of the experimental and theoretical challenges that serve as a motivation for this PhD project. In Chapter 2, a general theoretical description for thermophoresis is formulated using the theory of non-equilibrium thermodynamics. The colloidal flux is split up into an interfacial single-colloid contribution and a bulk contribution, followed by a determination of transport coefficients based on Onsager’s reciprocal relations. It is further shown how the phenomenological expression of the thermophoretic flux can be recovered when the fluid is at steady-state. The results issuing from this description are then discussed and compared to other existing approaches, some of which are shown to neglect the hydrodynamic character of colloidal thermophoresis. Chapter 3 is dedicated to the validation of the introduced theoretical framework by means of computer simulations, using a simulation technique known as multi-particle collision dynamics. More specifically, the dependence of the thermophoretic force on different system parameters is examined and deviations from the theoretical prediction are explained by an advective distortion of interfacial fluid properties at the colloidal surface. Chapter 4 presents steady-state measurements of functionalised colloids in a temperature gradient, showing how the addition of molecular surface groups increases the experimental complexity of thermophoretic motion. The relaxation process behind this steady-state is also studied, to determine how the relaxation speed depends on the applied temperature gradient. In chapter 5, a general conclusion is drawn from the presented work and its implications are briefly discussed in relation to the current state of knowledge. Finally, the discussion is closed with an outlook on remaining challenges in understanding colloidal motion that could be the subject of future research.
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Delamare, Jérôme. "Suspensions magnétiques partiellement passives." Grenoble INPG, 1994. http://www.theses.fr/1994INPG0004.
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Les suspensions magnétiques permettent la lévitation d'un corps sans contact. Un mobile peut ainsi être déplacé à grande vitesse sans engendrer de frottement ni d'usure. Les applications de ces systèmes sont essentiellement circulaires (turbines, volant d'inertie, centrifugeuse, machine outils. . . ) mais peuvent ainsi être linéaires (train. . . ). Les suspensions magnétiques sont déjà utilisées dans l'industrie mais leur prix de revient, dû à l'asservissement de tous les degrés de liberté de la partie suspendue, freine leur expansion. L'étude porte sur les suspensions magnétiques dont une partie des degrés de liberté est contrôlé par des paliers autonomes à aimants permanents. Les associations de paliers permettant de réaliser une suspension sont décrites ainsi que les motorisations possibles et les systèmes d'amortissement. La réalisation d'un prototype a mis en évidence les avantages et les inconvénients d'une suspension ne possédant qu'un seul axe asservi
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Baloyi, Jane Tsakane. "Precautionary suspensions in the public service : reflections from South Africa." Thesis, University of Limpopo, 2013. http://hdl.handle.net/10386/1180.
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Thesis (LLM ( Labour Law)) --University of Limpopo, 2013.The study will analyse the fairness or unfairness of precautionary suspensions and the rights of employees in the Public Service who are placed on precautionary suspensions with reference to section 23(1) of the Constitution of the Republic of South Africa, 1996, which states that: (1) “ Everyone has the right to fair labour practices” Section 186(2)(b) of the Labour Relations Act 66 of 1995 defines what an unfair labour practice is with specific reference to a precautionary suspension. It reads thus: (2) “ Unfair labour practice means any unfair act or omission that arises between an employer and an employee involving – (b) the unfair suspension of an employee or any other unfair disciplinary action short of dismissal in respect of an employee” The study will also look at circumstances under which precautionary suspension is invoked on Senior Management Service employees in the public service in terms of chapter 7, clause .2.7(2) of the Senior Management Service Handbook, 2003. Decided cases will be referred to which shows that one of the reasons why many precautionary suspensions are set aside when challenged in court, is because some employees who are assigned to deal with labour issues in the government departments are not competent to deal with those issues. The issue of political appointments impacts directly on service delivery if people are appointed to positions because of political affiliation than competency.
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D'Ambrosio, Enzo. "Imagerie de suspensions pour la mesure des contraintes particulaires dans les suspensions non-browniennes." Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4045.
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Depuis les travaux précurseurs d’Einstein il y a plus d’un siècle, la rhéologie des suspensions est un domaine de la physique qui a grandement évolué mais qui reste encore largement incompris, en particulier lorsqu’il s’agit dessuspensions concentrées. De nos jours, il est reconnu que les contacts entre les particules solides composant une suspension régissent le comportement rhéologique des suspensions non-browniennes concentrées : ils en augmententla viscosité et entraînent des comportements non-newtoniens. Les contraintes particulaires sont également à l’origine de la migration induite par cisaillement observée dans différents types d’écoulement à bas nombre de Reynolds,comme le proposent plusieurs modèles dont le plus populaire est le Suspension Balance Model. Malheureusement, les mesures des contraintes particulaires sont assez rares et il est par conséquent assez difficile de tester les modèlesqui ont été proposés pour expliquer ou prédire la migration. Au cours de ma thèse, j’ai essayé de contribuer à combler ce manque en orientant mes recherches suivant deux grands axes. Le premier est d’étudier de manièremacroscopique l’impact de la forme des particules composant une suspension sur la viscosité de cisaillement et également sur la contribution des contacts à cette viscosité. En outre, je montre que les suspensions non-browniennes et non-colloïdales ont un comportement rhéofluidifiant qui peut être décrit correctement par l’introduction d’une fraction volumique de blocage qui dépend de la contrainte de cisaillement. Le second et principal axe de recherche que j’ai suivi concerne une étude locale du comportement rhéologique d’une suspension dans deux cas distincts. Dans un des cas, les particules et le fluide suspendant ont la même densité, dans l’autre, les particules sédimentent sous l’effet de la gravité et sont resuspendues par un écoulement de cisaillement. J’ai réalisé un montage expérimental qui me permet d’imager la suspension pour mesurer localement non seulement la concentration en particules mais également le taux de cisaillement. Des mesures locales, je déduis d’une part la variation de la viscosité de cisaillement avec la fraction volumique de particules et la contrainte de cisaillement et, d’autre part la variation des contraintes normales particulaires dans la direction du gradient de vitesse et de la vorticité. Je mets par ailleurs enévidence des différences significatives dans l’écoulement d’une suspension suivant que la gravité joue un rôle ou non. En particulier, je montre que la migration radiale observée dans un écoulement de Couette cylindrique à large entrefer est beaucoup moins prononcée que ce que prévoit le Suspension Balance Model si les particules n’ont pas la même densité que le fluide suspendantMany studies have been done on the rheology of suspensions since the previous work of Einstein at the beginning of the 20th century but many scientific puzzles still remain, especially when the concentration increases. Nowadays, we know that the solid contact between particles rules the behavior of non Brownian concentrated suspensions : it increases the viscosity, inducesbehavior more complex than the basic Newtonian model and are responsible for phenomenon of migrations of solid particles inside a suspension. Naturally, theoretical models as the Suspension Balance Model which predict and describe the behavior of a sheared non Brownian suspension deals with these non hydrodynamic interactions. But there is a lack of experimental measurements to confront these predictions. Indeed, it is very difficult to measure experimentally the contribution of solid particles to the total stress of suspension and this is precisely what I’ve tried to do during these last three years. I’ve organized my work following two lines of research. The first one is a macroscopic study of the rheological behavior of different suspensions where the particle form varies from a suspension to another. Therewith, I show that non-Brownian and non-colloidal suspensions have a shear thinning behavior which can be correctly captured by the introduction of a jamming volumefraction which is shear stress-dependant. The second line of research is the biggest part of my work. Thanks to an experimental home-made set up, I study locally the behavior of a non Brownian suspension in two cases : with or without buoyancy effects. Matching the refractive index of the particles and of the fluid, I manage to image the particles inside the suspensions subjected to a shear flow in order to determine the concentration and the velocity fields. From these local measurements, I deduce on the one hand the variation of the shear viscosity with particle volume fraction and shear stress and, on the otherhand the variation of the normal particle stresses in the direction of the velocity gradient and the vorticity. I also show that there are significant differences in the flow of a suspension depending on whether gravity plays a role or not. More precisely, I show that the radial migration observed in a cylindrical large gap Couette flow is much less pronounced than what the Suspension Balance Model predicts if the particles do not have the same density as the suspending liquid
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Vu, Thai Son. "Rhéologie des suspensions non newtoniennes." Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00598310.
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Au cours de ce travail, nous nous sommes attachés à prédire les caractéristiques rhéologiques de suspensions de particules dans des situations non newtoniennes. Nous avons tout d'abord étudié expérimentalement le comportement rhéologique de suspensions bidisperses de particules non colloïdales et non browniennes immergées dans un fluide à seuil dans les situations où les interactions entre particules sont hydrodynamiques (mécaniques). Nous avons montré que l'influence de la polydispersité des particules sur le module élastique et le seuil de contrainte de la suspension pouvait être décrit en utilisant un modèle d'empilement développé pour les matériaux granulaires secs. Deux relations analytiques simples permettant d'estimer le module élastique et la contrainte seuil d'une suspension non newtonienne polydisperse en fonction des caractéristiques des constituants ont alors été proposées et validées. Nous nous sommes ensuite intéressés à la prédiction des caractéristiques globales de suspensions contenant une forte concentration de particules de taille différente dans le cadre d'une approche par changement d'échelle. Pour cela, nous avons mis en uvre une approche par motifs morphologiques permettant la prise en compte de paramètres géométriques tels que la distribution de tailles des inclusions ou les distances entre particules voisines. Les résultats de ce modèle ont été validés par comparaison avec des données expérimentales de la littérature. Nous avons ensuite montré que les modèles morphologiques permettaient également de décrire l'évolution des modules complexes d'un matériau thixotrope subissant une transition de phase liquide-solide due à la croissance et la percolation d'un réseau de particules attractives. Dans la dernière partie de cette étude, nous avons étudié expérimentalement l'influence de l'histoire de cisaillement sur la structuration et la déstructuration d'une suspension colloïdale thixotrope
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Mortazavi, Ramin. "Simulation of fine powder suspensions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0015/MQ53593.pdf.
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Raghavendra, Souharda. "Compliant multi-link vehicle suspensions." Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1219852205/.
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Mikulencak, Duane Richard. "Inertial effects in dilute suspensions." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/11026.
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Ju, Shuohui. "Electroosmotic dewatering of bentonite suspensions." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59868.
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Electroosmotic dewatering of Bentonite suspensions under conditions of constant DC voltage and constant DC current was investigated experimentally in a column 5 cm in diameter. The suspensions were prepared with CaCl$ sb2$ in distilled water with concentrations up to 1 M. The initial solid content was between 9.1 wt% and 26 wt% and the initial bed height ranged from 1.0 cm to 5.2 cm. Constant voltages from 4.0 V to 8.0 V and constant currents from 90 mA to 110 mA were used.Electroosmosis removed 20-60% of the water with energy expenditures well below the energy required to vaporize the water. Higher voltages or currents removed more water. Removal rates were increased by the addition of CaCl$ sb2$. The lowest bed height (1 cm) gave the lowest energy of dewatering, but the final water removal was low. For constant voltage experiments with an initial field strength of 2.8 V/cm, bed heights around 2 cm gave the highest water removal. The initial solid content had little effect on the final solid content. The Helmholtz/Smoluchowski theory did not predict correctly the effects of electrolyte concentration, solid content and bed height on the rate of electroosmotic dewatering.
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Balasubramanian, Karthick. "Coaxial electrohydrodynamic atomisation of suspensions." Thesis, Queen Mary, University of London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439086.
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Eldridge, Matthew David. "Computer simulation of colloidal suspensions." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359410.
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Holmes, D. M. "Lateral drying of ceramic suspensions." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604187.
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Many ceramic processing routes, such as tape casting, screen-printing and ink jet printing, involve deposition of a suspension of ceramic particles in a prescribed shape on a substrate. As the liquid evaporates from the suspension, the particles pack together and liquid leaves the pores. In water-based suspensions, these processes often occur at fronts that move from the edge to the centre of the drying layer. This is known as lateral drying. As drying proceeds, the body can change shape, residual stresses can develop and cracking can occur. However, existing models cannot predict either the shape changes that occur or adequately explain why the drying layer cracks. To study this, the drying behaviour of layers of alumina suspensions was investigated experimentally. Measurements were made of the movement of lateral fronts, the changes in local thickness and the activity at the surface of the layers, and the cracking behaviour and the dried thickness profiles were studied. By considering the redistribution of liquid at the first lateral front, where particles pack together, an expression for the thickness profile of the dried layers has been derived. Mass loss data, together with the local thickness measurements, suggest that the particles do not come into touching contact at this first front. Instead, a collapse event occurs when the repulsive layers between the particles are overcome. The development of stress in a drying layer is generally attributed to the build-up of capillary pressure at the surface of the body. However, this causes compression of the particle network, despite the constraint to shrinkage imposed by the substrate, and therefore cannot explain why cracking occurs. Here, it is proposed that the driving force for cracking actually arises from the collapse event. This predicts that cracking should occur while the space between the particles is still filled with liquid. This is consistent with the measurements of surface activity and local thickness, and the cracking behaviour observed.
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Zackrisson, Samuel. "Suspensions with small, spherical particles." Thesis, KTH, Numerisk analys, NA, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168014.
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Feasibly computable analytic solutions for systems of many particles in fluid dynamics and electrostatics are few and far-between. Simulations and numerical approximations are essential to studying these systems. This is commonly done without directly calculating the interacting field between particles. In this report a method utilizing the spectral accuracy of the Fourier transform is studied to calculate particle velocities via the surrounding fluid velocity field. The method is applied to a periodic cube of a suspension of small, spherical particles sedimenting in a fluid affected by gravity, in an attempt to mimic the behaviour of a similar infinite system. Results for a few particles qualitatively relate the shape of the solution to the choice of interpolation between particles to grid and quantitatively maps some convergence properties of a certain class of interpolating functions, cardinal B-splines. The properties of the method on the periodic system are also examined and compared to a similar study of the infinite system for many, ~1000, particles.Det finns sällan vare sig tillräckligt med beräkningskraft eller analytiska lösningar för stora flerpartikelsystem i fluidsmekanik och elektrostatik. Simuleringar och numeriska approximationer är därför grundläggande metoder för att studera dessa system. Partiklarnas banor beräknas vanligen utan att direkt beräkna fluidens hastighetsfält. I denna rapport studeras en simuleringsmetod som utnyttjar den spektrala noggrannheten hos fouriertransformen för att finna partikelhastigheterna via fluidens hastighetsfält. Metoden tillämpas på en periodisk kub med en suspension av små, sfäriska partiklar påverkade av gravitationen i en fluid i ett försök att efterlikna beteendet hos ett likadant, icke-periodiska system. Resultat för fåpartikelsystem förklarar kvalitativt formen på lösningsströmningar i förhållande till valet av inerpolation mellan partikelpositioner och rutnät, samt kvantitativt kartlägger vissa konvergensegenskaper hos en viss klass av interpolerande funktioner, cardinal B-splines. Egenskaperna hos denna metod på det periodiska systemet studeras och jämförs med en liknande studie av det icke-periodiska systemet för många, ~1000, partiklar.
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Kim, Jinho. "Floc properties in stirred suspensions." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268458.
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Parker, A. R. "Particle interactions in fluid suspensions." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384501.
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Bibbó, Miguel Angel. "Rheology of semiconcentrated fiber suspensions." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14875.
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Haffner, Benjamin. "Stabilité des suspensions fortement aérées." Thesis, Paris Est, 2015. http://www.theses.fr/2015PEST1095/document.
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Nous étudions le drainage des mousses de suspension granulaire. Nos paramètres de contrôle sont : la fraction en gaz, la taille des bulles, celle des particules et la fraction volumique de celles-ci dans la phase interstitielle. En premier lieu, nous mesurons la proportion de liquide et de particules retenus dans le réseau de la mousse en fonction des paramètres cités précédemment. Ces mesures réalisées une fois le drainage terminé apportent des éléments de compréhension indispensables à la description des vitesses de drainage. Nous montrons également que certaines combinaisons de nos paramètres d'étude conduisent au blocage du système gaz, liquide, solide. Dans un second temps, nous avons identifié différents régimes de cinétique de drainage, nous montrons qu'ils sont contrôlés par deux paramètres : (i) le rapport lambda de la taille des particules et de la taille des constrictions du réseau, (ii) la fraction en particules dans la phase interstitielle phi. Le point clé pour comprendre ces régimes est le piégeage des particules dans la mousse qui peut avoir deux origines : (i) par piégeage collectif (jamming) qui peut survenir pour des fractions étonnamment basses à cause de la géométrie du réseau interstitiel, (ii) la capture individuelle des particules par la mousse lorsque leur taille devient supérieure à celle des constrictions du réseau interstitiel. Des particules encore plus grosses sont exclues du réseau et participent à une remontée de la vitesse de drainage, faisant apparaître un minimum pour le régime correspondant à la capture individuelle. La fraction granulaire de la phase interstitielle est aussi essentielle, le drainage pouvant être stoppé pour des fractions suffisamment élevées lorsque lambda est judicieusement choisi. Ce travail propose des pistes prometteuses pour la stabilité des matériaux triphasiquesWe study the drainage of granular suspensions foams. Our control parameters are the gas fraction, the bubble size, the particles size and the interstitial particle fraction. First, we measure the proportion of liquid and particles retained in the foam network as function of the above mentioned parameters. These measurements are performed when the drainage is over, they are essential for the description of drainage velocity. We show that certain combinations of our study parameters lead to the jamming of the three-phase system : gas, liquid, solid. Secondly, we highlight different regimes of drainage velocity, we show that is controlled by two parameters : (i) lambda, the ratio of the particle size and constriction size, (ii) the fraction of particles in the interstitial network : phi. The key to understand these regimes is the trapping of particles in the foam : (i) the jamming, which may occur for surprisingly low fractions due to the geometry of the pore network, (ii) the particles captured by the foam network when they become larger than the constrictions network. Finally, larger particles excluded from the network increase the drainage velocity, as a consequence the minimum for the velocity corresponds to the individual capture. The granular fraction of the suspension in the foam network is the other key parameter. Especially, the drainage can be stopped for sufficiently high fractions for certain values of lambda. This work offers promising outlook for the stability of three-phase materials
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Forsyth, Claire. "Complex flow of concentrated suspensions." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25403.
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This thesis describes work done to investigate the effects of flow on concentrated suspensions. The work is largely about the effects of flow on concentrated colloidal suspensions, however, a short section on the effects of flow on concentrated granular suspensions is also given. Concentrated suspensions show a variety of complex flow behaviour. They can show Newtonian, shear thinning or shear thickening behaviour, depending on the applied stress or shear rate and concentration. The shear thickening behaviour may be discontinuous and this is characterised by a dramatic increase in viscosity above a certain threshold of stress. This is thought to be closely related to flow induced jamming, which can be defined as the conversion of a liquid system into a solid by imposed stress. This behaviour is not well understood and can cause significant complications in industry. It also has potential applications, for example in shock absorption. Due to their complexities and potential applications, gaining a better understanding of how shear thickening and jamming materials behave is of interest and forms the basis of this thesis. In this work, bespoke shear cells and a novel method to detect flow induced jamming were designed and utilised. This allowed jamming to be visualised and evaluated quantitatively. Conditions where jamming occurs were mapped out and the effects of parameters such as concentration, shear stress, system geometry and system confinement were investigated. This, and an analysis of jamming statistics, allowed ways to prevent and control jamming to be identified and a better understanding of the system to be achieved. Such an analysis is lacking in literature. The conditions where jamming was detected using the novel equipment matched well with measurements using a commercial rheometer. This supported the idea of discontinuous shear thickening and flow induced jamming being closely related. The studies allowed a mechanism for flow induced jamming and discontinuous shear thickening to be proposed. By designing and using novel equipment that is not commercially available, a better understanding of the effects of flow on concentrated suspensions was achieved. This could ultimately lead to a better understanding of complex flow systems and lead to more efficient processes.
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Williams, Richard Andrew. "Electrochemical behaviour of ferrosilicon suspensions." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47302.
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Ham-Pichavant, Frédérique. "Mécanismes d'égouttage des suspensions fibreuses." Bordeaux 1, 1994. http://www.theses.fr/1994BOR10580.
Full textAbstract:
Sur une machine a papier, on distingue deux zones en ce qui concerne l'egouttage: la zone ou l'egouttage se fait par gravite et celle ou le vide est necessaire pour continuer l'extraction de l'eau. Les deux mecanismes sont totalement differents et il importe donc de pouvoir les caracteriser separement. Nous avons mis au point sur l'appareil britt jar des tests nous permettant d'etudier l'egouttage naturel et la reponse au vide. En modifiant le comportement a l'egouttage des pates par raffinage et traitement enzymatique, nous avons pu mettre en evidence les parametres qui influent sur l'aptitude a l'egouttage des suspensions fibreuses
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Lemaire, Élisabeth. "Suspensions electro et magneto-rheologiques." Paris 7, 1992. http://www.theses.fr/1992PA077258.
Full textAbstract:
Nous avons etudie l'effet de l'application d'un champ electrique ou magnetique a des suspensions colloidales de deux types: une suspension er de spheres de silice hydratee dans de l'huile silicone et une suspension aqueuse de particules superparamagnetiques. Le champ applique dote chaque particule d'un moment magnetique ou electrique, selon le cas. Si l'energie d'interaction electrique ou magnetique domine l'agitation brownienne, les particules se rassemblent en fibrilles alignees dans la direction du champ. Cette anisotropie de structure s'accompagne de changements rheologiques remarquables. Nous les avons caracterises par l'apparition d'une contrainte seuil et d'un module d'elasticite. La contrainte seuil ainsi que l'allure generale du rheogramme ont ete obtenus par des experiences de rheometrie stationnaire menees dans differentes geometries: capillaire cylindrique, plan/plan, couette cylindrique; le module de rigidite, determine a l'aide d'un rheometre oscillant plan/plan. Les resultats experimentaux ont ete interpretes sur la base du calcul de la force d'interaction de deux spheres dielectriques ou paramagnetiques soumises a un champ electrique ou magnetique respectivement. Ce modele conduit a des predictions en accord satisfaisant avec les resultats experimentaux cependant que la structure de la suspension ne peut etre modelisee par un ensemble de chaines isolees comme le calcul le suppose. Plus que de chaines, la suspension, soumise a un champ, est formee de fibrilles dont la section peut contenir un grand nombre de particules. Des experiences d'optique, etudiant la transmission des suspensions structurees, nous ont permis de caracteriser le changement de structure, consecutif a l'application du champ, par la taille des domaines formes et le champ minimum a appliquer pour observer leur formation
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Tang, Yanfei. "Stratification in Drying Particle Suspensions." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/87435.
Full textAbstract:
This thesis is on molecular dynamics studies of drying suspensions of bidisperse nanoparticle mixtures. I first use an explicit solvent model to investigate how the structure of the dry film depends on the evaporation rate of the solvent and the initial volume fractions of the nanoparticles. My simulation results show that the particle mixtures stratify according to their sizes when the suspensions are quickly dried, consistent with the prediction of recent theories. I further show that stratification can be controlled using thermophoresis induced by a thermal gradient imposed on the drying suspension. To model larger systems on longer time scales, I explore implicit solvent models of drying particle suspensions in which the solvent is treated as a uniform viscous background and the liquid-vapor interface is replaced by a potential barrier that confines all the solutes in the solution. Drying is then modeled as a process in which the location of the confining potential is moved. In order to clarify the physical foundation of this moving interface method, I analyze the meniscus on the outside of a circular cylinder and apply the results to understand the capillary force experienced by a spherical particle at a liquid-vapor interface. My analyses show that the capillary force is approximately linear with the displacement of the particle from its equilibrium location at the interface. An analytical expression is derived for the corresponding spring constant that depends on the surface tension and lateral span of the interface and the particle radius. I further show that with a careful mapping, both explicit and implicit solvent models yield similar stratification behavior for drying suspensions of bidisperse particles. Finally, I apply the moving interface method based on an implicit solvent to study the drying of various soft matter solutions, including a solution film of a mixture of polymers and nanoparticles, a suspension droplet of bidisperse nanoparticles, a solution droplet of a polymer blend, and a solution droplet of diblock copolymers.PHD
Drying is a ubiquitous phenomenon. In this thesis, I use molecular dynamics methods to simulate the drying of a suspension of a bidisperse mixture of nanoparticles that have two different radii. First, I use a model in which the solvent is included explicitly as point particles and the nanoparticles are modeled as spheres with finite radii. Their trajectories are generated by numerically solving the Newtonian equations of motion for all the particles in the system. My simulations show that the bidisperse nanoparticle mixtures stratify according to their sizes after drying. For example, a “small-on-top” stratified film can be produced in which the smaller nanoparticles are distributed on top of the larger particles in the drying film. I further use a similar model to demonstrate that stratification can be controlled by imposing a thermal gradient on the drying suspension. I then map an explicit solvent system to an implicit one in which the solvent is treated as a uniform viscous background and only the nanoparticles are kept. The physical foundation of this mapping is clarified. I compare simulations using the explicit and implicit solvent models and show that similar stratification behavior emerge in both models. Therefore, the implicit solvent model can be applied to study much larger systems on longer time scales. Finally, I apply the implicit solvent model to study the drying of various soft matter solutions, including a solution film of a mixture of polymers and nanoparticles, a droplet of a bidisperse nanoparticle suspension, a solution droplet of a polymer blend, and a droplet of a diblock copolymer solution.
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Griese, Andrew Herman. "Relaxation behavior of dense suspensions." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127924.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 16-17).
Dense suspensions of solid particles in Newtonian fluids exhibit a variety of non-Newtonian behaviors depending on the shear stress applied to the suspension and the particle mass fraction ([mathematical symbol]m). Suspensions at sufficiently high fm shear-thicken dramatically and eventually shear jam, showing behaviors typified by solids. But, little is known about how dense suspensions relax out of this stressed rheological state. To understand the relaxation behavior of a cornstarch/water dense suspension, samples are prepared at different fm, in the range that shows dramatic shear thickening, between 54.5% and 58.5% cornstarch. Each sample is formed into drops and kept in the stressed state through dynamic shearing using a B&K permanent magnet shaker, then allowed to relax. We show that dense suspensions relax with two distinct timescales. A short timescale that is independent of [mathematical symbol]m, denoting the settling of the drop onto the flat surface, and a longer timescale that is governed by the viscosity of the dense suspension and increases as [mathematical symbol]m increases above 55.75%. Our work provides an understanding of how a dense suspension relaxes out of a shear-thickened state.
by Andrew Herman Griese.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Bonnoit, Claire. "Ecoulement de suspensions granulaires modèles." Paris 6, 2009. https://pastel.archives-ouvertes.fr/tel-00463534.
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Hanotin, Caroline. "Rhéophysique des suspensions granulaires vibrées." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0150/document.
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Quantifier l'impact des vibrations sur les propriétés rhéologiques des suspensions granulaires trouve son intérêt en géophysique et dans de nombreux secteurs industriels. Par exemple, les mécanismes de liquéfaction des sols sous l'effet d'une secousse demeurent mal connus à ce jour. L'objet de cette thèse est d'apporter une compréhension fondamentale des modifications induites par les vibrations sur les propriétés physiques et mécaniques d'un système modèle composé de billes de verre sphériques et monodisperses immergées dans un fluide newtonien en concentration dense (Φ≈0.61). Dans un premier temps, le comportement rhéologique macroscopique global des suspensions a été étudié à l'aide d'un rhéomètre couplé à une cellule vibrante. Les vibrations font disparaître la contrainte seuil du matériau et font apparaître un plateau newtonien contrôlé par une compétition entre les contraintes de lubrification et les contraintes frictionnelles. Un autre type d'expérience, la rhéométrie à chute de bille par Imagerie par Résonance Magnétique, montre des résultats similaires. Dans un second temps, la dynamique de réorganisation locale des grains a été sondée grâce à des expériences de diffusion de la lumière faisant appel à une caméra CCD et fondées sur l'analyse des fluctuations d'intensité des figures de speckle. Cette technique a permis de sonder la dynamique des particules aux temps longs. Il est apparu que le temps caractéristique de relaxation obtenu est relié à la viscosité au plateau newtonien de la suspension granulaire vibrée, ce qui a permis d'établir un lien entre le comportement rhéologique macroscopique des échantillons et la dynamique diffusionnelle à l'échelle du grainQuantify the impact of vibrations on the rheological properties of granular suspensions is of paramount importance in many environmental or industrial areas. For example, the soil liquefaction mechanisms, as a result of an earthquake, remain poorly understood by now. The purpose of this thesis is to provide a fundamental understanding of the modifications induced by the vibrations on physical and mechanical properties of a model concentrated suspension (Φ≈0.61), made up of spherical monodisperse glass beads immersed in a Newtonian fluid. In a first step, the macroscopic rheological behavior of this system has been studied using a classical rheometer coupled with a vibrating cell. The vibrations induce the vanishing of the yield stress of the material and the emergence of a Newtonian plateau at low shear. Thus, it has been shown that the viscosity of the suspension is controlled by a competition between lubrication and frictional stresses. Another type of experiment, the falling ball rheometry by Magnetic Resonance Imaging, shows similar results. In a second step, the local dynamics of the grains was probed by diffusing wave spectroscopy using a CCD camera based on the analysis of the intensity fluctuations of speckle patterns. This technique allowed to probe the dynamics of particles at long times. It appears that the characteristic relaxation time obtained is related to the suspension viscosity, thereby linking the macroscopic rheological properties to the diffusional dynamics at the grain scale
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Furbank, Roy Jeffrey. "Drop formation from particulate suspensions." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-05172004-100527/unrestricted/furbank%5Froy%5Fj%5F200407%5Fphd.pdf.
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Thesis (Ph. D.)--School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2005. Directed by F. Joseph Schork.Schork, F. Joseph, Committee Chair ; Morris, Jeffrey F., Committee Co-Chair ; Forney, Larry J., Committee Member ; Breedveld, Victor, Committee Member ; Mucha, Peter J., Committee Member ; Smith, Marc K., Committee Member. Includes bibliographical references.
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Wade, Theresa. "The electroacoustics of milk suspensions." Thesis, The University of Sydney, 1996. https://hdl.handle.net/2123/27567.
Full textAbstract:
The zeta potential and size distribution of casein micelles and fat globules from
bovine milk have been investigated with the relatively new technique of electroacoustics.
This technique requires no dilution or change of environment of the casein micelles or fat
globules. The zeta potential obtained at natural pH for casein micelles from a
commercial skim milk suspension was —18 mV and the median diameter was 0.2 um A
zeta potential of —19 mV was obtained for homogenized fat globules from a commercial
milk suspension, a zeta potential of —22 mV was obtained for natural fat globules from a
commercial cream suspension and a zeta potential of —36 mV was obtained for fat
globules from a recombined milk suspension. The median sizes obtained for the fat
globules from the various suspensions were reasonable but at present electroacoustics
cannot give a true indication of the spread of the size distribution for the fat globules.
Two processes used in the dairy industry were investigated with electroacoustics.
The size and zeta potential of casein micelles were monitored during acidification and
renneting. For both processes it was found that the trends in zeta potential obtained
with electroacoustics during the two processes agreed extremely well with trends
reported in the literature. However, the trends in size observed with electroacoustics
were different fiom trends reported in the literature. The difi‘erences in the trends in size
of the casein micelles obtained during the renneting and acidification processes have
been explained in terms of structural changes occurring to the casein micelles during the
two processes. Hence the technique of electroacoustics can not only measure zeta
potential and apparent particle size but may be able to monitor structural changes in
particles during various processes.
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Chachanidze, Revaz. "Collective phenomena in blood suspensions." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0632.
Full textAbstract:
Ce travail a été réalisé dans l’I. R. P. H. E. (Institut de Recherche sur les Phénomènes Hors Équilibre), unité de recherche de l’Université d’Aix-Marseille en collaboration avec l’Université de la Sarre, la Faculté de Physique Expérimentale. Cette étude est consacrée à une meilleure compréhension de la microcirculation du sang in vitro, ainsi que des phénomènes collectifs qui prennent place dans la microcirculation. Il se concentre principalement sur la margination en fonction du contrast de rigidité dans une suspension de globules rouges. L’expérience modale a été développée pour étudier la margination, causée exclusivement par le contraste de la déformabilité entre les deux sous-populations de globules rouges: les saines et les rigidifiéesThis work was carried out in collaboration between I.R.P.H.E. (Institut de Recherche sur les Phénomènes Hors Équilibre), research unit of Aix-Marseille University and University of Saarland, Faculty of Experimental Physics (Naturwissenschaftlich-Technische Fakultät der Universität des Saarlandes) and aims to investigate microcirculatory hydrodynamics of blood in vitro. The study is dedicated to better understanding of complex collective phenomena that take place in microcirculation of blood through microfluidic in vitro experiments. It mainly focuses rigidity based margination in suspension of RBCs. For this purpose, model experiment was developed to examine margination caused exclusively by contrast of deformability between two sub-populations of RBCs
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Injety, Sahana. "Formulation of a nevirapine co-crystal as a liquid dosage form." University of the Western Cape, 2016. http://hdl.handle.net/11394/5060.
Full textAbstract:
Magister Pharmaceuticae - MPharmCo-crystals are a solid phase phenomena that could enhance the physicochemical properties of an active pharmaceutical ingredient. A co-crystal has never been incorporated into a liquid dosage form with the assurance of maintaining its co-crystal state until absorption under defined conditions. This study aims to develop a liquid formulation with a nevirapine co-crystal. A protocol was developed to investigate all the five co-formers that were used to make the nevirapine co-crystals to-date. The most appropriate co-former was selected for a liquid dosage form to study the integrity and the scaling up of the co-crystal in a suspension formulation. Co-formers used were viz. saccharin, glutaric acid, salicylic acid, rac-tartaric acid and maleic acid. These were characterized according to their physical, chemical, pharmacological and pharmaceutical properties. A grading scale was used to select the most appropriate co-former for a suspension formulation. Comparatively, saccharin produced the best combination of physical, chemical, pharmacological and pharmaceutical properties, especially with regard to the particle size and the specific gravity which proved to be very useful as optimal criteria for suspension formulation. Upon selection of the ideal co-former, scale-up of the nevirapine saccharin co-crystal was performed from a small scale of 350 mg to a large scale of 5 g. Nevirapine-saccharin (NVSC) co-crystals were prepared utilizing the slow evaporation technique, using methanol as the solvent and the percentage yield of the co-crystals were > 80 %. The identity of co-crystals was confirmed using hot stage microscopy (HSM), differential scanning calorimetry (DSC), fourier transform infra- red (FTIR) and thermogravimetric analysis (TGA). Three co-crystal suspension formulations were prepared using the excipients identified in the branded, Viramune® suspension, with each formulation containing viscosity enhancers such as aerosil 200, carbopol 971G and carbopol 974P. To ascertain the co- crystal integrity in the suspension, it was filtered and the filtrate was identified with DSC and FTIR while the filtered solution was identified with ultraviolet spectroscopy (UV). The co-crystal suspension formulation with optimal pH, viscosity and assurance of co-crystal integrity was the carbopol 974P formulation. The UV and DSC of the filtrate of the suspension revealed that the co-crystal had not separated into its individual components and remained intact while in suspension form irrespective of the excipients added. This formulation proceeded to the quality control stage. It was assessed for its pH, viscosity and dissolution according to the USP 32 standards and compared to the branded nevirapine suspension, Viramune ®, presently on the market. The suspension was characterized for particle size, zeta potential and polydispersity index. The dissolution results assayed by High Performance Liquid Chromatography (HPLC) revealed a drug release of 86 % in the Viramune® suspension while the NVSC co- crystal suspension achieved a drug release of 94% within 30 minutes of dissolution.
National Research Foundation (NRF)
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Mouroko-Mitoulou, Thomas. "Filtration de suspensions minérales avec formation d'un gâteau liquéfiable : cas d'une suspension de carbonate de calcium." Compiègne, 2002. http://www.theses.fr/2002COMP1430.
Full textAbstract:
L'importance économique croissante des suspensions colloi͏̈dales hautement concentrées, a conduit à la recherche des procédés alternatifs à la concentration (déshydratation) thermiqueo Les suspensions faiblement ou moyennement concentrées ont été déshydratées en présence de dispersants par des procédés mécaniques à faible consommation d'énergie utilisables sur filtre-presse (filtrationcompression, accompagné ou non par un champ électrique) en vue d'obtenir des gâteaux hautement concentrés en solides et fluidifiés 0 La filtration-compression en présence de dispersants chimiques (Coatex DV798, Coatex DV806, Coatex DV 67, Coatex DV 765, Coatex DV 834, Coatex DV 828) a permis d'obtenir des gâteaux relativement fluides ayant une siccité comprise entre 69 et 74%. La filtration en présence de dispersants, assistée d'un champ électrique a permis d'obtenir des gâteaux légèrement plus secs que la filtration ordinaire, difficilement liquéfiableso La filtration-compression en présence de dispersants suivie d'une compression assistée d'un champ électrique a permis d'obtenir des gâteaux relativement plus secs que les gâteaux obtenus par filtration-compression Gusqu'à 80% de siccité avec le dispersant cationique Coatex DV 67), mais non liquéfiés. La présence des agents dispersants en amont d'un procédé de filtration-compression s'accompagne d'une perte de dispersant dans le filtrat, qui rend presque inévitable la mise aux normes de ces quantités de filtrats difficilement recyclables. Finalement un procédé original à été mis au point à savoir la filtration en deux étapes qui consiste à former un seul gâteau par la filtration successive de deux suspensions: la première ne contient aucun agents dispersant, contrairement à la deuxième suspensiono Ce procédé à été modélisé et appliqué aussi bien sur les suspensions du carbonate de calcium que certaines autres suspensions de particules minérales (le carbonate de calcium précipité, le carbonate de calcium "OMY A 50", le kaolin, l'hydroxyde d'aluminium et le dioxyde de titane)o Comparativement aux résultats de la filtration en une seule étape, les siccités des différents gâteaux sont sensiblement voisines en revanche la viscosité des gâteaux obtenus par filtration en deux étapes est améliorée et contrairement aux filtrats totalement contaminés de la filtration en une seule étape, la quantité de filtrat lors de la filtration en deux étapes est fortement réduite et donc facilement recyclableo Les résultats obtenus au laboratoire ont été confirmés à l'échelle de filtre-presse pilote, en outre les gâteaux formés ont été comparés aux gâteaux obtenus par concentration thermique des suspensions, principalement leur stabilité sur une période de 8 jourso En plus du fait de la facile application, le concept de la filtration en deux étapes est peut être appliqué à la défloculation in situ ainsi qu'au lavage des gâteaux de filtration.
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Périn, Frédéric. "Application de la methode d'homogeneisation aux suspensions de fibres longues et aux suspensions multidisperses de particules." Paris 6, 1994. http://www.theses.fr/1994PA066423.
Full textAbstract:
La methode d'homogeneisation est appliquee a une suspension bidimensionnelle concentree et localement periodique de fibres orientees plongees dans un fluide visqueux incompressible. Dans la premiere partie, on considere un ecoulement longitudinal. La suspension se comporte comme un fluide newtonien anisotrope, le tenseur de viscosite etant du second ordre et entierement determine par la microstructure qui n'evolue pas dans le temps. Dans la deuxieme partie, on considere un ecoulement transverse. La suspension se comporte comme un fluide non newtonien anisotrope, le tenseur de viscosite etant du quatrieme ordre et entierement determine par la microstructure qui evolue dans le temps en restant localement periodique. De plus, il apparait dans les equations globales de mouvement des termes d'inertie inattendus. Si la microstructure presente des symetries, on peut obtenir des bornes pour certains des coefficients de viscosite rencontres dans ces deux mouvements. Les resultats numeriques montrent que ces bornes constituent de bonnes approximations des valeurs calculees numeriquement et que la concentration ne peut a elle seule decrire le comportement global du milieu. Dans la troisieme partie, on montre que les resultats obtenus toujours par la methode d'homogeneisation et concernant les suspensions tridimensionnelles concentrees de particules s'etendent au cas des suspensions multidisperses de particules. De meme, dans la quatrieme partie, on montre que les resultats obtenus dans la premiere partie s'etendent au cas des suspensions multidisperses de fibres
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Wafra, Mustapha. "Sédimentation en présence d'agrégation dans les suspensions colloïdales : Etude expérimentale des suspensions de carbonate de calcium." Paris 13, 1994. http://www.theses.fr/1994PA132009.
Full textAbstract:
La sédimentation des suspensions colloïdales de carbonate de calcium en présence d'agrégation présente une grande variété de comportements suivant la fraction volumique des particules. Après avoir présenté une analyse bibliographique du sujet et une étude de la caractérisation physico-chimique et de l'état de dispersion des suspensions étudiées, l'essentiel de la thèse est consacré à la description et à l'analyse des mesures de vitesse de sédimentation. En particulier, l'utilisation d'une approche en lois d'échelle et la prise en compte de la répartition spatiale des particules (empilement compact d'agrégats fractals) ont permis d'interpréter les comportements originaux observés, les valeurs de la fraction volumique séparant les différents domaines de variation ainsi que les résultats des mesures de vitesse de sédimentation.
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Navarro, Argemí Eloy. "Hydrodynamic effects on active colloidal suspensions." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/665006.
Full textAbstract:
The goal of this thesis is studying hydrodynamic effects on active colloidal suspensions. Hydrodynamic interaction is propagated through the fluid in which the colloids displace due to the flow they create during their motion. It can lead to the emergence of collective phenomena, such as the self-assembly of more complex structures. Hydrodynamic interactions are not the only present in the system, since other forces may be acting between colloids, or there can be external fields acting on them such as gravity. We present our study for two different systems: magnetic colloids and Janus particles. When applying a circular magnetic field, we can induce a rotation to a particle possessing a magnetic moment. Due to the coupling of the flow with the one created by surrounding particles and with system interfaces, a rotor will eventually self-propel. Two magnetic moments interact with each other through the magnetic dipole-dipole force, which tends to align them into arrays. We study how the balance between hydrodynamic, magnetic and gravitational forces determines the morphology of the structures magnetic colloids can form. Janus particles have two faces with different chemical properties, thus the interaction between them depends on their relative orientation. We study the morphology and order of the structures that can emerge for these particles as a function of the intensity, sign and reach of the interaction between them, as well as the type of flow they create when self-propelling. Methodologically, we have combined the use of far-field theory to draw analytical expressions that have given us qualitative insight on the results we could expect with high-performance computing simulations which have allowed us to extend our study to bigger systems.En aquesta tesi ens proposem estudiar els efectes hidrodinàmics en suspensions col·loidals actives. La interacció hidrodinàmica es propaga a través del fluid en el que es desplacen els col·loids degut al flux que ells mateixos creen durant el seu moviment, podent donar lloc a l’emergència de fenòmens col·lectius, com l’autoorganització en estructures més complexes. Les interaccions hidrodinàmiques no són les úniques presents en el sistema, ja que pot haver-hi d’altres forces actuant entre els col·loids, o podem considerar l’efecte d’altres camps com la gravetat. Presentem el nostre estudi per a dos sistemes diferents: col·loids magnètics i partícules Janus. En aplicar un camp magnètic circular, es pot induir una rotació a una partícula que posseeixi un moment magnètic. Degut a l’acoplament del flux amb el creat per altres partícules i les parets del sistema, un rotor pot acabar desplaçant-se. Dos moments magnètics interactuen entre ells mitjançant la força dipolar, que afavoreix el seu alineament i la formació de cadenes de col·loids. Estudiem com el balanç entre interaccions hidrodinàmiques, magnètiques i efectes gravitatoris afecta a la morfologia de les estructures que poden formar els col·loids magnètics. Les partícules Janus tenen dues cares amb propietats químiques diferents, quelcom que dóna lloc a una interacció entre elles que depèn de la seva orientació relativa. Estudiem les estructures que poden aparèixer per a aquestes partícules com a funció de la intensitat, signe i abast d’aquesta interacció, així com de la forma del flux que creen en desplaçar-se. Metodològicament, hem combinat expressions analítiques aproximades per tenir una idea qualitativa dels fenòmens que hom pot esperar amb simulacions per ordinador per poder estudiar els fenòmens col·lectius en sistemes de més partícules.
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Angélique, Deboeuf. "Interactions hydrodynamiques dans les suspensions macroscopiques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00423044.
Full textAbstract:
Ce travail concerne les suspensions macroscopiques en régime visqueux, pour lesquelles les interactions sont purement hydrodynamiques, au travers de deux expériences modèles.La première, de nature rhéologique, vise à caractériser les contraintes de la phase particulaire dans une suspension isodense cisaillée. Elle met en évidence une pression des particules, proportionnelle au cisaillement imposé, analogue à la pression osmotique, proportionnelle à la température dans les systèmes Browniens. Les résultats obtenus pour des concentrations en particules allant de 0.30 à 0.50, indiquent que les contraintes normales induites dépendent fortement de la concentration.
La seconde expérience concerne des suspensions bidisperses fluidisées de particules plus denses que le fluide. L'efficacité de la fluidisation à ségréger ou à mélanger les particules de tailles différentes est testée pour différents débits imposés. Pour des rapports de tailles assez grands et quelle que soit la concentration, il existe un état ségrégé stationnaire (grosses billes seules surmontées de petites seules). Les vitesses de fronts de ségrégation permettent de discriminer les modèles empiriques proposés dans la littérature : le modèle de Funamizu & Takakuwa rend compte des mesures, avec un seul paramètre ajustable. En revanche, lorsque le rapport de tailles est inférieur à 4/3, et pour une certaine gamme de concentration, aucun état stationnaire n'est observé. Les suspensions oscillent entre états mélangés et états partiellement ségrégés avec une période variant avec la composition et la concentration : le processus de ségrégation est interrompu par un phénomène de mélange encore inexpliqué.
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Astorsdotter, Jennifer. "Dewatering Cellulose Nanofibril Suspensions through Centrifugation." Thesis, KTH, Skolan för kemivetenskap (CHE), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215079.
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Cellulose nanofibrils (CNF) is a renewable material with unique strength properties. A difficulty in CNF production is that CNF suspensions contain large amounts of water. If CNF suspension volume can be decreased by dewatering facilitated by centrifugation, then transportation costs and storage costs can be reduced. The aim of this thesis is to investigate the impact various parameters have on CNF centrifugation dewatering and identify optimal conditions for maximal water removal. A laboratory study was conducted using four materials; 2.0 w% enzymatically treated CNF (CNF1), 1.9 w% carboxymethylated CNF (CNF2) and two commercial samples (1.9 w% CNFA and 1.8 w% CNFB). The main method was analytical centrifugation up to 2330 g. Parameters tested were initial concentration before centrifugation, temperature, NaCl addition, pH, and applied solid compressive pressure (g-force and surface weight). In addition to centrifugation experiments the four materials were characterized with laser diffraction, UV-vis absorption, Dynamic light scattering, and dry weight measurements. Analysis of the experimental data collected show that increase in initial concentration give a higher final concentration, but less water is removed. Furthermore, temperature changes have no effect on separation of CNF and water. At an applied solid compressive pressure of 3 kPa and initial concentration at 1.5 w% the concentrations 5.5 w%, 1.5 w%, 4.0 w%, and 4.3 w% can be reach for CNF1, CNF2, CNFA, and CNFB respectively. After extrapolation of polynomial functions fitted to experimental data an applied solid compressive pressure of 22 kPa and initial concentration at 1:5 w%, the concentrations 9.1 w%, 1.5 w%, 6.9 w%, and 7.9 w% are predicted for CNF1, CNF2, CNFA, and CNFB respectively. The thickening of CNF suspensions achieved and predicted in this thesis implies possibilities for large amounts of water removal, e.g. the water content in a CNF1 suspension is reduced from 65.7 litres/kg CNF to 10.0 litres/kg CNF at the solid compressive pressure 22 kPa. The concentrations at 22 kPa are determined by extrapolation from experimental data <3 kPa solid compressive pressure. The carboxymethylated CNF2 can not be dewatered unless it is diluted or if salt or pH is adjusted. This is directly correlated to the electrostatic forces in the suspension and the Debye length. Addition of salt or lowered pH also eliminate any concentration gradients in diluted and centrifuged CNF2 suspensions.Cellulosa nanofibriller (CNF) är ett förnybart material med unika styrkeegenskaper. En svårighet med produktion av CNF är att CNF suspensioner innehåller stora mängder vatten. Om volymerna av CNF suspensioner kan minskas med avvattning genom centrifugering, då kan transport- och lagerkostnader sänkas. Målet med det här examensarbetet är att undersöka vilken inverkan olika parametrar har på CNF-avvattning genom centrifugering och identifiera optimala förhållanden för maximalt avlägsnande av vatten. En laboratoriestudie utfördes på fyra olika material. De fyra materialen är 2 w% enzymatiskt behandlad CNF (CNF1), 1.9 w% karboxymetylerad CNF (CNF2) och två kommersiella prover (1.9 w% CNFA och 1.8 w% CNFB). Den huvudsakliga metoden var analytisk centrifugering upp till maximalt 2330 g. De testade parametrarna var initial koncentration innan centrifugering, temperatur, NaCl tillsats, pH, och applicerat fast kompressionstryck (g-kraft och ytvikt). Förutom centrifugeringsexperimenten så karaktäriserades the fyra mmaterialen med laser diffraktion, UV-vis absorption, dynamisk ljusspridning och vägningar av torrhalt. Analys av den experimentella data som insamlats visar att en ökad initial koncentration ger en högre slutkoncnentration, men mindre vatten kan bortföras. Temperaturförändringar har ingen effekt på separation av CNF och vatten. Vid ett applicerat fast kompressibelt tryck på 3 kPa och en initial koncentration 1.5 w% kan koncentrationerna 5.5 w%, 1.5 w%, 4.0 w%, och 4.3 w% nås för CNF1, CNF2, CNFA, och CNFB. Efter extrapolering av polynoma funktioner passad till experimentell data förutspås att koncentrationerna 9.1 w%, 1.5 w%, 6.9 w%, och 7.9 w% kan nås för CNF1, CNF2, CNFA, and CNFB vid 22 kPa och en initial koncentration på 1.5 w%. Förtjockningen av CNF suspensioner som kan, eller förutspås kunna nås genom centrifugering i det här examensarbetet innebär att det är möjligt att avlägsna stora mängder vatten, till exempel kan vatteninnehållet i CNF1 minskas från 65.7 liter/kg CNF till 10.0 liter/kg CNF vid 22 kPa fast kompressionstryck. Koncentrationerna vid 22 kPa fast kompressionstryck är extrapolerade från exprimentell data <3 kPa fast kompressionstryck. Den karboy- metylerade CNF2 kan inte avvattnas om den inte späds ut eller om salt eller pH justeras. Detta är direkt kopplat till de elektrostatiska krafterna i suspensionen och Debye längden. Tillsats av salt eller sänkt pH eliminerar också de koncentrationsgradienter som kan förekomma i utspädda centrifugerade CNF2 suspensioner.
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Ullah, Khan Asad. "Rheology and processing of ceramic suspensions." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7308.
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Barker, Dean Anthony. "Thermal processing of highly filled suspensions." Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/252100.
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A novel continuous casting process used to form a highly filled, thermoplastic paste into a net shape ceramic body has been investigated, a method termed thermal paste processing (TPP). TPP uses a long cylindrical die cooled below the solidification temperature of the continuous phase, so that the extrudate merges from the die as a solid rod. Thermal processes were investigated using standard and novel power compensated DSC techniques, yielding both enthalpic response and thermal transport properties. The rheological behaviour was characterised over 9 decades of apparent shear rate, for temperatures from the melt to mushy range. Steady and dynamic shear responses were probed with controlled stress and controlled strain rotational rheometers, using smooth or serrated parallel disks, concentric cylinders, or vane-type geometries. Capillary rheometry using the multi-pass technique was also performed. The rheological characterisation revealed a mismatch between expected and measured onset temperatures when using a parallel disk rheometer; this led to the measurement and simulation of the sample’s and rheometer’s temperature fields. These results were incorporated into the description of the paste’s rheological response to temperature. The thermal and rheological parameters yielded by the above characterisations were incorporated into a 2-D axisymmetric model of the TPP die system using the finite element method (FEM). The numerical code performance was compared against three suitable benchmark problems reported in the literature. The results from one case concerning the melting of gallium in a square cavity revealed a possible cause of circulation cell instability observed in many numerical results, but not respond experimentally. Predictions from the numerical simulations were compared with equivalent experimental data from an instrumented TPP die system. The formulation variations demonstrate poor to good agreement with experimental data.
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Guda, Swathi Mucha Peter John. "Rayleigh-Taylor instability in sedimenting suspensions." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,1276.
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Thesis (M.S.)--University of North Carolina at Chapel Hill, 2006.Title from electronic title page (viewed Mar. 27, 2008). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mathematics Applied Mathematics." Discipline: Mathematics; Department/School: Mathematics.
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Abubakar, Muhiddin. "Controlled sedimentation of concentrated colloidal suspensions." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439508.
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Dreiss, CeÌcile Ayako. "Structure and interactions of colloidal suspensions." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404422.
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Pancholi, Ketan Pinakin. "Microbubbling of viscous liquids and suspensions." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/17281/.
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This research comprises of device designing and processing of biomaterial suspensions based on co-flowing medium and air. The preparation of stable microbubble suspensions is fundamental to a wide range of technological applications across the scientific, engineering, medical and industrial sectors; from the production of basic foodstuffs to the self-assembly of smart materials. A key requirement in such preparation is to control the size distribution (i.e. mean and standard deviation) of the resulting microbubbles, with ideally a monodispersion being achieved. Such quality control is important because when the microbubbles are used in, for example, in ultrasound imaging, the response of such a microbubble to ultrasound excitation is strongly influenced by the radius and the thickness of the microbubble and also the mechanical properties of any coating material. This response, in tum, determines the amplitude and frequency of the ultrasound signal scattered by the microbubbles and the threshold for microbubble destruction. In first part of the work, a device is designed and optimized to microbubble silicone oils of different viscosities. All the important physical parameters like liquid and air flow rate, capillary diameter, gap between two capillaries, viscosity and surface tension are investigated to understand the mechanisms of bubble formation and to idealise the processing technique. The condition of bubble formation; a ratio of air to liquid pressure is found to be related to viscosity of liquid which is important in materials processing. Bubble dynamics are also modelled to predict the air jet diameter which can control the diameter of bubble being produced. It was shown that air jet diameter has a strong relationship to viscosity of the liquid. Secondly, using a similar device and technique, lipid suspension and nano gold particulate colloids are microbubbled to show that process is suitable for producing near monodisperse microbubbles with more than 20 minutes life time. These microbubbles have immediate application as ultrasound contrast agent and drug delivery vehicle. Moreover, it is also found that nano-particulate reinforced bubbles can enhance the non-linearity of backscatter at low amplitude pressure. To further reduce the diameter of bubbles, a hybrid flow focussing and electrospraying device is developed to show that monodisperse size of bubbles less than 10 μm can be produced. This process has been syslematically studied to conclude that the product of applied voltage and flow ratio governs the diameter of bubbles generated.