Dissertations / Theses on the topic 'Rheology of suspensions'
To see the other types of publications on this topic, follow the link: Rheology of suspensions.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Rheology of suspensions.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Purnomo, Eko Hari. "Rheology of aging suspensions." Enschede : University of Twente [Host], 2008. http://doc.utwente.nl/59045.
Full text
2
Bibbó, Miguel Angel. "Rheology of semiconcentrated fiber suspensions." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14875.
Full text
3
Ullah, Khan Asad. "Rheology and processing of ceramic suspensions." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7308.
Full text
4
Rossi, Sylvia Elena. "Polymer adsorption and rheology of clay suspensions." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267740.
Full text
5
Jamali, Safa. "Rheology of Colloidal Suspensions: A Computational Study." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1432054369.
Full text
6
Shaikh, Saif. "Dynamics and rheology of concentrated suspensions of rigid fibers." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0495.
Full textAbstract:
Une étude combinant expériences et analyses est menée afin de rationaliser la dynamique et la rhéologie des suspensions très concentrées de fibres rigides, non colloïdales dans un fluide newtonien. Des mesures rhéologiques couplées à des mesures de la microstructure sont réalisées à l’aide de plusieurs dispositifs expérimentaux permettant d’analyser différents types de géométries et d’écoulements. Des expériences de rhéologie standards (rhéologie à volume contrôlé), ainsi qu’une méthode de rhéologie non-conventionnelle (rhéologie à pression contrôlée) sont associées afin de mesurer la contrainte de cisaillement, la pression de la phase particulaire et la fraction volumique des suspensions très concentrées. Un autre dispositif expérimental a été conçu dans le but d’étudier la microstructure (distribution spatiale et distribution d’orientations) d’une suspension de fibres rigides dans un écoulement de Poiseuille oscillant. Alors que ce type d’écoulement est réversible pour un liquide newtonien, dans le cas d’une suspension concentrée, les interactions entre particules introduisent des changements irréversibles de microstructure. Cette microstructure est affectée et a un effet sur l’écoulement imposé, cette dépendance non-linéaire incluant les interactions hydrodynamiques. L’objectif de ces expériences est d’apporter un éclairage sur des effets tels que la rhéofluidification observée à fort taux de cisaillement et sur le démixage dû à la migration induite par cisaillementA combined work of experiments and data analyses is proposed to investigate the dynamics and rheology of highly concentrated suspensions of non-colloidal rigid rods in a Newtonian fluid. Detailed measurements of the rheology and the microstructure are made using a variety of experimental devices with different geometries and imposed flows. Standard rheology experiments (volume-controlled rheology), as well as a novel method of rheometry, are carried out to measure torques, particle pressures, and volume fractions at high concentration (pressure-controlled rheology). Another experiment has been designed and constructed to study the microstructure (spatial and orientation distribution) of a suspension of rigid rods in an oscillatory parabolic flow. Though the flow is reversible in these systems, the changes in the microstructure are irreversibile in the case of concentrated suspensions due to particle interactions. The microstructure is affected by, and has an effect, on the imposed flows; this non-linear dependency includes hydrodynamic interactions. The purpose of these experiments is to gain insight into phenomena such as apparent shear-thinning at high shear rates and demixing due to shear-induced migration
7
Sakabe, Hiroshi. "The structure and rheology of strongly interacting suspensions." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283944.
Full text
8
Shafiei, Sabet Sadaf. "Shear rheology of cellulose nanocrystal (CNC) aqueous suspensions." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45679.
Full textAbstract:
Scientific and commercial interests in renewable nanomaterials have been receiving increasing attention over the years. Cellulose nanocrystal (CNC) derived from entirely renewable resources promises wide applicability owing to its high strength, chirality, self-assembly and electromagnetic properties. In this thesis the rheology of CNC aqueous suspensions was studied and the rheological behaviour was correlated with their microstructure. It has been found that the CNC aqueous suspensions experience two microstructural transitions by increasing CNC concentration: a transition from isotropic to chiral nematic liquid crystal occurs above a first critical concentration, and by further increasing concentration, the suspensions go through another transition from chiral nematic liquid crystal to gel above a second critical concentration. The viscosity profile of anisotropic suspensions shows a three-region behaviour characteristic of liquid crystals, and after gel formation a single shear thinning is observed over the whole investigated range.
CNC suspensions possessing a higher degree of sulfation have more tendency to form anisotropic chiral nematic structures, and form gels at relatively higher concentration compared to those with a lower degree of sulfation. Sonication up to 1000 J/g CNC, breaks all the aggregates in the system and significantly decreases the viscosity. Although the sonication-induced decrease in viscosity levels off through further sonication (>1000 J/g CNC), it still affects the viscosity of anisotropic suspensions at low shear rates by increasing the size of chiral nematic domains.
The effects of adding NaCl to CNC aqueous suspensions have been evaluated in different concentration regimes: isotropic, anisotropic chiral nematic, and gel. For isotropic samples and gels, the viscosity decreases by the addition of NaCl up to 5 mM. For anisotropic samples, on the other hand, the viscosity at low shear rates increases by addition of NaCl up to 5 mM due to decrease in chiral nematic domain size. However, at high shear rates, where all the domains are broken, the viscosity decreases when adding NaCl. Further addition of NaCl (>5 mM) results in extensive aggregation in suspension, and thus the viscosity increases.
9
Ma, Wing Kui Anson. "The microstructure and rheology of carbon nanotube suspensions." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611278.
Full text
10
Avery, Michael Philip. "Dense suspensions : nanostructure, rheology and applications in printing." Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.730855.
Full text
11
Dbouk, Talib. "Rheology of concentrated suspensions & shear-induced migration." Nice, 2011. http://www.theses.fr/2011NICE4060.
Full textAbstract:
Lorsqu’une suspension concentrée est en écoulement, il est fréquent d’observer que la concentration en particules ne reste pas homogène mais que les particules migrent vers des régions préférentielles de l’écoulement. Globalement, il existe deux types de modèles pour décrire cette interaction entre l’écoulement et la structure qui apparaît dans la suspension. Les premiers sont assez phénoménologiques et reposent sur l’étude des collisions qui surviennent entre les particules en écoulement. Ils donnent lieu à une description de la migration en termes de diffusion des particules. Le second modèle, appelé « Suspension Balance Model » (SBM), fait appel à l’action des contraintes normales d’origine particulaires engendrées par l’écoulement. Ce modèle semble très pertinent mais son utilisation souffre du manque de données sur les contraintes normales dans les suspensions. Ce manuscrit rapporte une étude expérimentale et numérique de la rhéologie et de la migration induite par un écoulement dans des suspensions non-browniennes concentrées. La partie expérimentale consiste à mesurer, en géométrie torsionnelle plan-plan, la viscosité, les deux différences de contraintes normales et le tenseur des contraintes particulaires. Les contraintes particulaires déterminées expérimentalement sont alors injectées dans le « Suspension Balance Model » qui relie le flux de particules à la divergence du tenseur des contraintes particulaires, dans le cas d’un écoulement de cisaillement simple. Les équations couplées de la conservation de la masse, des particules et du moment d’inertie sont implémentées dans OpenFOAMr et résolues par la méthode des volumes finis. Les résultats numériques sont comparés à des résultats numériques et expérimentaux de la littérature. Enfin, le SBM est généralisé pour être utilisé dans tout type d’écoulement à 2 dimensions ; les cas du cisaillement d’un nuage de particules et de l’effet de la gravité dans un écoulement de Couette horizontal sont traitésThis thesis deals with an experimental and numerical investigation of the phenomenon of shear-induced particle migration in inhomogeneous shear flows of mono-dispersed non-colloidal suspensions at neglected inertia. Varieties of diffusion flux models that predict the shear-induced migration were presented. However, in this work, the Suspension Balance Model (SBM) is adopted. The latter describes the migration flux of particles as the divergence of the particles Stress tensor. According to the need for the different measurable parameters in this Model, a new experiment was developed for measuring the viscosity, the two Normal Stress Differences and the particle stress tensor of mono-dispersed non-Brownian suspensions of hard spheres flowing between rotating parallel disks over a wide range of concentrations (2. 20-0. 46). The original SBM is modified based on the new measurements. The Finite Volume Method via the OpenFOAM package is used as the technique to solve the problem numerically. Solutions are generated and results are compared to similar ones generated with the original model. Finally, the SBM model is extended into two-dimensional situations within a general Frame-invariant structure that takes into account the local kinematics of the suspension
12
Derakhshandeh, Babak. "Rheology of low to medium consistency pulp fibre suspensions." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37371.
Full textAbstract:
Papermaking is a major industry to manufacture products vital to education, communication, and packaging. Most operations in this industry deal with the flow of different mass concentrations of pulp suspensions. Therefore, the flow properties (rheology) of pulp suspensions are of great importance for the optimal functionality of most unit operations in the industry.
Yield stress is one of the most important rheological properties in designing process equipment, thus needs to be determined by a reliable technique. Two established and extensively used methods for determining yield stress were compared with a velocimetry technique. The yield stresses were determined for commercial pulp suspensions at fibre mass concentrations of 0.5 to 5 wt. %. The results were compared and models were proposed to predict the yield stress as a function of fibre mass concentration. The yield stress values obtained by the velocimetry technique were found to be the most reliable.
Conventional rheometry and local velocimetry techniques were further used to study the flow behaviour of pulp suspensions beyond the yield stress. Pulp suspensions were found to be shear-thinning up to a certain high shear rate. The Herschel–Bulkley constitutive equation was used to fit the local steady-state velocity profiles and to predict the steady-state flow curves obtained by conventional rheometry. Conventional rheometry was found to fail at low shear rates due to the presence of wall slip. Consistency between the various sets of data was found for all suspensions studied.
Finally, the same approach was used to study thixotropy and transient flow behaviour of concentrated pulp suspension of 6 wt.%. Pulp was found to exhibit a plateau in the flow curve where a slight increase in the shear stress generated a jump in the corresponding shear rate, implying the occurrence of shear banding. The velocity profiles were found to be discontinuous in the vicinity of the yielding radius where a Herschel-Bulkley model failed to predict the flow. Shear history and the time of rest prior to the measurement were found to play a significant role on the rheology and the local velocity profiles of pulp suspension.
13
Xu, Jianhua. "Rheology of polymeric suspensions polymer nanocomposites and waterborne coatings /." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1127317214.
Full text
14
Ganley, William John. "Structure and rheology of clay suspensions and Pickering emulsions." Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.730906.
Full text
15
Wilson, Laurence. "Optical force measurements in concentrated colloidal suspensions." Thesis, University of Edinburgh, 2007. http://hdl.handle.net/1842/3220.
Full textAbstract:
This work concerns the construction and testing of an optical tweezers-based force transducer, and its application to a hard-sphere colloidal system. A particle in an optical trap forward-scatters a fraction of the trapping light, which is collected in order to give high-resolution information on the trapped particle’s position relative to the trap centre. The system is then calibrated to convert particle displacements to forces. The colloid used in this study is a density- and refractive index-matched suspension of PMMA particles, radius 860 ± 70nm, with volume fractions in the range φ = 40 → 62%. Passive microrheological measurements have yielded information about rearrangements in a tracer’s cage of nearest neighbours, as well as highly localised measurements of the high-frequency viscosity, where the presence of the colloidal host causes around a tenfold increase compared to the bare solvent case. Measurements have also demonstrated the effect of sample history on local short-time self-diffusion coefficient, with perturbations caused by translating a particle within the sample taking up to an hour to relax in a φ = 58% sample. The high resolution particle tracking offered by this technique has also allowed for the first measurement of structure at a shorter lengthscale than the ‘dynamic cage size’ observed using other experimental techniques. In addition, active measurements have shown the emergence of a yield stress on the order of 5Pa as the volume fraction approaches the glass transition at φ ≈ 58%.
16
Llewellin, Edward William. "The rheology of bubble bearing magmas : theory and experiments." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251071.
Full text
17
Davies, Russell Martin. "Zeolites in ceramic suspensions : a study of rheological effect." Thesis, Keele University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288426.
Full textAbstract:
Molecular sieves with low silicon to aluminium ratio exhibit high ion-exchange capacity and fast exchange kinetics for the removal of divalent cations, such as Mg2 +, Ca2 + and Sr>. Owing to their unique structure and properties and the similarity of their composition to many ceramic materials, zeolites are also promising materials for use in the ceramics industry. The processing of modem ceramics formulations, e.g. glaze and coating suspensions. generally requires constant rheological characteristics over time. Glaze suspension rheology. however. usually changes with time due to the continual dissolution of the solid fraction, i.e. the frit. This study, therefore, evaluates the suitability of zeolites as ion exchangers and rheological stabilisers for the glaze industry. It is important that the zeolites in question are able to withstand the conditions of high shear and temperature experienced during ball milling without loss of crystallinity. This is detennined in this study using a variety of techniques including TGA, XRD, XRF. SEM. FTIR, zeta potential and particle size measurements. Other important properties of zeolites include their surface charge characteristics, ion exchange capacity and rheology modifying behaviour. These properties are evaluated using zeta potential, ICP. and rheology measurements respectively. Zeta potential measurements show that the surface charge properties of zeolites are a function of the silica and alumina components at the surfaces of the respective structures. i.e. the silicon to aluminium ratio. TGA, XRD, XRF, FTIR, ICP and zeta potential results show that the crystallinity of each zeolite analysed is independent of ball milling, whereas, ion exchange capacity decreases significantly after milling. The ion exchange capacity of each zeolite, however, is sufficient to cause a marked decrease in the total divalent ion concentration in the liquid phase of each glaze suspension after milling. The monovalent ion concentration in the liquid phase of each suspension may increase or decrease depending on the type of zeolite employed. The changing rheology of each suspension, on zeolite addition, also varies depending on the initial composition of the glaze components, the liquid phase ion concentration and the type of zeolite used. Time resolved measurements show that the rheology of each suspension, in the presence of zeolite, continues to change up to eight weeks after milling due to further dissolution of the glaze components. This study, therefore, concludes that although zeolites are effective at modifying the liquid phase ion concentration and rheology of concentrated glaze suspensions, they are unable to completely stabilise suspension rheology over time. The ion exchange ability of zeolites. however, may still prove to be of benefit to the glaze industry, especially in the removal of Ca2+ and Mg2+ ions from hard water sources.
18
Harrison, Andrew William. "One and two point micro-rheology of hard sphere suspensions." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5764.
Full textAbstract:
The material that is covered in this thesis concerns the calibration and application of a set of optical tweezers to be used for one- and two-point micro-rheology experiments on hard sphere colloidal suspensions. The colloidal suspensions that were used in this study were all quasi-monodisperse density- and refractive index-matched PMMA particles that had a radii, a = 0:90 ± 0:05μm or a = 0:86 ± 0:07 for one-point microrheology experiments and radii a = 0:90 ± 0:05μm or a = 0:133 ± 0:010μm for the two-point micro-rheology experiments. By collecting the forward scattered light from a single optically trapped particle the particle's displacements in time were used to determine passive microviscosity, η(Passive) μ , for colloidal suspension in the range of 0:10 < Ø < 0:57 and comparison with literature data has been made and agreement found. Actively dragging an optically trapped particle through suspensions with volume fractions of the same range has yielded the active microviscosities, η(Active) μ , for both high and low shear regimes, displaying shear thinning behaviour. Comparison to literature data has been made and agreement found as well. Collecting the forward scattered light from two optically trapped particles has been used to determine the cross-correlated motion of the two particles in bare solvent and in suspensions with volume fraction Ø = 0:02. The friction coefficients ξ1;1 and ξ1;2 were extracted from the cross-correlated motion of the particles and agreement was found with theoretical predictions for bare solvent only. The suspensions with volume fraction Ø = 0:02 were found to have a friction coefficient ξ1;1 that was greater than what theory predicted with the suspension with bath particles a = 0:90 ± 0:05μm had the greater magnitude. The magnitude ξ1;2 was found to decrease for the suspension with bath particles of radius a = 0:133 ± 0:010μm and to increase for the suspension with bath particles a = 0:90 ± 0:05μm.
19
Jomha, A. I. "The power requirements for mixing concentrated solid/liquid suspensions." Thesis, University of Bradford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376348.
Full text
20
Hess, Andreas [Verfasser], and Nuri [Akademischer Betreuer] Aksel. "Rheology of polyelectrolyte multilayer modified suspensions / Andreas Hess. Betreuer: Nuri Aksel." Bayreuth : Universität Bayreuth, 2014. http://d-nb.info/1059907976/34.
Full text
21
Laganapan, Aleena Maria. "Rheology and structure of ceramic suspensions under constraints : a computational study." Thesis, Limoges, 2015. http://www.theses.fr/2015LIMO0082/document.
Full textAbstract:
L'enjeu principal de cette thèse est de comprendre et prédire les propriétés structurales et rhéologiques de suspensions colloïdales en tenant compte d'éléments complexes tels que (1) les interactions hydrodynamiques (IHs) et/ou (2) des forces extérieures. Nous employons dans cette thèse deux des techniques numériques les plus rapides de la littérature: la dynamique brownienne standard (BD), pour les systèmes où les IHs peuvent être ignorées; et la technique hybride "stochastic rotation dynamics - molecular dynamics" (SRD-MD), pour les systèmes où les IHs doivent être incorporées.Trois systèmes colloïdaux différents ont été étudiés. Le premier est un système de sphères dures soumis à un cisaillement, où le but a été de vérifier que l'introduction des IHs dans la SRD-MD peut correctement reproduire la relation entre la viscosité et la fraction volumique. Les résultats de viscosité sont en accord avec les résultats connus, qu'ils soient analytiques, numériques et expérimentaux. Le second système consiste en une suspension d'alumine, pour laquelle les interactions sont décrites par la théorie DLVO (Derjaguin-Landau-Verwey-Overbeek). Les simulations montrent que le seuil de percolation (phi_c) diminue lorsque la profondeur du puits de potentiel augmente. De plus, nous observons que la prise en compte des IHs tend à former des structures plus allongées également, par rapport aux structures obtenues sans les IHs. Les valeurs de phi_c obtenues dans les simulations sont en bon accord avec celles estimées par le modèle de la contrainte seuil (YODEL) établi par Flatt et Bowen. Le troisième système comporte deux types de colloïdes qui interagissent par un potentiel de Yukawa. Ce système binaire est soumis à l'influence d'un mur attractif. Nous montrons que la présence d'un mur attractif peut altérer la structure cristalline des agrégats à la surface telle qu'une structure de type CsCl qui se forme au lieu de la structure métastable de type NaCl. Finalement, nous avons réalisé une étude préliminaire par SRD-MD de suspensions soumises à un cisaillement oscillant. Nous montrons que lorsque la suspension est soumise au cisaillement oscillant en même temps que l'agrégation se produit, des structures plus compactes se formentThe main objective of this thesis is to predict and understand the structural and rheological properties of colloidal suspensions when (1) hydrodynamic interactions (HIs) and/or (2) external forces are present. We employ two of the fastest techniques in literature: Brownian dynamics (BD), for systems without HIs; and the hybrid "stochastic rotation dynamics - molecular dynamics" (SRD-MD) for systems with HIs. Three different systems were studied. The first is a system of hard spheres subjected to shear, where the goal was to ensure that SRD-MD can correctly reproduce the viscosity vs. volume fraction relationship. The results are consistent with known analytical, numerical and experimental data. The second system is an alumina suspension described by the DLVO theory (Derjaguin-Landau-Verwey-Overbeek). The simulations show that the percolation threshold (phi_c) decreases as the depth of the potential well increases. Moreover, we note that HIs tend to form more elongated structures compared to the systems without HIs. The phi_c values obtained are in good agreement with those estimated by Flatt and Bowen's yield stress model (YODEL). The third system consists of binary colloids that interact by Yukawa potential and subjected to the influence of an attractive wall. We show that the presence of an attractive wall may alter the crystalline structures such that CsCl crystals are formed instead of the metastable NaCl crystals. Finally, we conducted a preliminary study of suspensions under an oscillating shear. We show that when the aggregation process suspension coincides with the oscillatory motion, more compact structures are formed
22
Madraki, Fatemeh. "Shear Thickening in Non-Brownian Suspensions." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1584354185678102.
Full text
23
Clausen, Jonathan Ryan. "The effect of particle deformation on the rheology and microstructure of noncolloidal suspensions." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34680.
Full textAbstract:
In order to study suspensions of deformable particles, a hybrid numerical technique was developed that combined a lattice-Boltzmann (LB) fluid solver with a finite element (FE) solid-phase solver. The LB method accurately recovered Navier-Stokes hydrodynamics, while the linear FE method accurately modeled deformation of fluid-filled elastic capsules for moderate levels of deformation. The LB/FE technique was extended using the Message Passing Interface (MPI) to allow scalable simulations on leading-class distributed memory supercomputers.
An extensive series of validations were conducted using model problems, and the LB/FE method was found to accurately capture proper capsule dynamics and fluid hydrodynamics. The dilute-limit rheology was studied, and the individual normal stresses were accurately measured. An extension to the analytical theory for viscoelastic spheres [R. Roscoe. J. Fluid Mech., 28(02):273-93, 1967] was proposed that included the isotropic pressure disturbance. Single-body deformation was found to have a small negative (tensile) effect on the particle pressure.
Next, the rheology and microstructure of dense suspensions of elastic capsules were probed in detail. As elastic deformation was introduced to the capsules, the rheology exhibited rapid changes. Moderate amounts of shear thinning were observed, and the first normal stress difference showed a rapid increase from a negative value for the rigid case, to a positive value for moderate levels of deformation. The particle pressure also demonstrated a decrease in compressive stresses as deformation increased. The corresponding changes in microstructure were quantified. Changes in particle self-diffusivity were also noted.
24
Guy, Ben Michael. "The physics of the flow of concentrated suspensions." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/29572.
Full textAbstract:
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.
25
Weisen, Albree Rae. "Thermorheological Dynamics of Glycerol-Based Colloidal Silica Suspensions." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1626785313712582.
Full text
26
Snook, Braden. "The dynamics of the microstructure and the rheology in suspensions of rigid particles." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4700.
Full textAbstract:
Des méthodes numériques et expérimentales ont été utilisées pour identifier la relation entre les propriétés macroscopiques et la microstructure d'une suspension contenant soit des sphères soit des fibres rigides. Pour les fibres, les résultats en utilisant un modèle numérique original indiquent que les contacts sont dominants dans la prédiction de la dynamique de la microstructure. Les résultats montrent en outre que les contacts doivent être inclus dans le calcul des contraintes afin de prédire avec précision les différences de contraintes normales. Des expériences ont été effectués pour mesurer les différences de contraintes normales et ont sont en accord avec les prédictions numériques. Cela valide le modèle développé et ses résultats. Les écarts avec les travaux antérieurs dans la littérature ont été examinées. Le temps nécessaire pour atteindre l'état d'équilibre et l'influence de confinement de la géométrie expérimentale peuvent être la source de ces différences. Pour les sphères, une expérience a été construite pour étudier la dynamique de la migration de particules dans un écoulement de Poiseuille. Nous avons mesuré la fraction volumique de particules avec une grande résolution ainsi que les distribution de vitesse. Les résultats dans le régime stationnaire de migration finale ont été jugés en excellent accord avec les précédentes simulations discrètes et les expériences dans des géométries et concentrations. La dynamique a été comparée à le modèle de bilan de suspension ('Suspension Balance Model'). L'accord avec ce modèle n'est bon qu'à grande fraction volumique. Des développements supplémentaires concernant la rhéologie utilisés dans le SBM sont nécessairesNumerical and experimental methods were used to reveal the complex relationship between the macroscopic properties and the microstructure of a suspension where either spheres or rigid fibers were considered. For fibers, results using a newly developed numerical model indicate that contacts are dominant in predicting the dynamics of the microstructure. The results show contacts must be included in calculating the stress in order to accurately predict the normal stress differences as well. Experiments measuring the normal stress differences were performed and were found to be in agreement with the numerical predictions, validating the model and its results. Discrepancies with previous work in the literature were examined. The long time required to reach steady state and the influence of confinement from the experimental geometry were found to be the source of these differences. For spheres, an experiment was built to study the dynamics of particle migration in parabolic flow. High-resolution particle volume fraction and velocity distribution measurements were made. Steady state results were found to be in excellent agreement with previous discrete element simulations and experiments at similar geometries and volume fractions. Dynamic results were compared to the suspension balance model (SBM). Excellent agreement with the SBM was exhibited only at the highest bulk particle volume fraction. Accordingly, additional development of the rheology used in the SBM is required to understand the role of the bulk volume fraction on its predictions. The results from this experiment will greatly aid this endeavor by providing the experimental data required for validation
27
Liberto, Teresa. "Physico-chemical study of calcite colloidal suspensions : from macroscopic rheology to microscopic interaction." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1140/document.
Full textAbstract:
La calcite (carbonate de calcium) est un matériau extrêmement répandu dans les roches telles que le marbre et comme constituant dans des domaines variés (bâtiment, pharmacie, papier, art). La compréhension des propriétés mécaniques des suspensions de calcite constitue une étape importante pour améliorer à la fois leur maniabilité ainsi que les propriétés finales du matériau fabriqué. Cette étude relie les propriétés rhéologiques (élasticité, écoulement) de ces suspensions à leurs interactions microscopiques. Les interactions attractives entre particules de calcite confèrent aux pâtes les propriétés de gels colloidaux caractérisés par un module élastique et une déformation critique, et ce pour une large gamme de concentrations. L'étude de ces grandeurs en fonction de la concentration a permis de mettre en évidence pour la première fois l'existence de deux régimes de déformation (liens forts et faibles) prédits théoriquement et de caractériser la dimension fractale. L'étude des interactions a été réalisée grâce à la mesure du potentiel Zeta des pâtes, du pH et au calcul de la longueur de Debye résultant de la force ionique. L'ajout d'additifs tels que la chaux ou la soude modifie les interactions. La chaux réduit fortement l'élasticité initiale des pâtes, facilitant leur maniabilité et renforçant la réactivité de la pâte en présence de CO2. L'ajout de soude augmente fortement l'attraction entre les particules ce qui se traduit à l'échelle macroscopique par l'existence de bandes de cisaillement. Cette manifestation de l'attraction entre colloïdes à l'échelle macroscopique avait été observée dans des émulsions concentrées mais encore jamais dans les gels colloïdauxCalcite (calcium carbonate) is an extremely widespread material that can be found naturally in rocks (i.e. marble, limestone) and is employed in many industrial fields such as paper filling, pharmaceutical, art or construction. Understanding the mechanical properties of calcite suspensions is a first step to improve the workability of the paste as well as the final properties of solid mineral materials. Macroscopic characterization of calcite suspensions via rheological measurements are linked to microscopic interactions, via DLVO analysis. Our calcite pastes are weakly attractive systems showing a typical colloidal gel behavior and characterized by an elastic shear modulus and a critical strain. The elastic domain of pure calcite suspensions is characterized for a wide range of volume concentrations. The deformation at the end of linearity exhibits a minimum versus concentration, a major prediction of colloidal gel theory, never verified so far. The interaction forces between particles are tuned by addition of simple ionic species. Rheological measurements are analyzed through DLVO calculations, obtained by chemical speciations and ζ potential measurements on dense suspensions. Addition of calcium hydroxide improves initially the workability of the paste, enhancing the reactivity when in contact with CO2. The role of interaction forces is also evaluated with flow measurements. The addition of sodium hydroxide increases strongly the attraction between particles, inducing shear bands at the macroscopic scale. This correlation is well known for emulsions but never verified so far for colloidal gels
28
Kotze, Reinhardt. "Rheological characterisation of highly concentrated mineral suspensions using an ultrasonic velocity profiler." Thesis, Cape Peninsula University of Technology, 2007. http://hdl.handle.net/20.500.11838/1150.
Full textAbstract:
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2007The rheological behaviour of non-Newtonian, highly concentrated and non-transparent fluids used in industry have so far been analysed using commercially available instruments, such as conventional rotational rheometers and tube viscometers. When dealing with the prediction of non-Newtonian flows in pipes, pipe fittings and open channels, most of the models used are empirical in nature. The fact that the fluids or slurries that are used normally are opaque, effectively narrows down the variety of applicable in-line rheometers even further, as these instruments are normally based on laser or visible light techniques, such as Laser Doppler Anemometry. Electrical Resistance Tomography is a non-invasive method used to look into opaque suspensions during pipe flow, but cannot be used to measure in-line rheometry. In this research, an Ultrasound Pulsed Echo Doppler Velocity Profile technique (UVP), in combination with a pressure difference (PD) was tested to provide in-line measurement of rheological parameters. The main objective ofthis research was to evaluate the capabilities of the UVP-PD technique for rheological characterisation of different concentrations of non-transparent non-Newtonian slurries. A unique pipe viscometer was designed and constructed. It consisted of four pipes, one of stainless steel and three of PVC, linked to an in-line mass-flow meter and equipped with two different ranges of pressure transducers on each pipe. The stainless steel pipe, with an inner diameter of 16 mm, was equipped with a specially designed flow adapter for in-line rheological characterisation using the UVP-PD method. The three PVC pipes with different diameters of 9 mm, 13 mm and 16 mm served as a tube viscometer for in-line rheological characterisation of mineral suspensions.
29
Guzmán, Jara Marcelo Andrés. "Non-Ideal rheology and spatial structures of bacterial suspensions in the semi-dilute regime." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/152138.
Full textAbstract:
Magíster en Ciencias, Mención FísicaEn esta tesis se presenta un estudio de la reología y de las estructuras espaciales que surgen en suspensiones de bacterias en el regimen semi-diluido. Debido al tamaño microscópico de las bacterias, su densidad y velocidad de propulsión, estas viven en un ambiente caracterizado por un bajo número de Reynolds, por lo que la fuerza y torque total sobre ellas son nulos. Por lo tanto, a primer orden, las perturbaciones en el campo de velocidades producidas por estos nadadores corresponde a un dipolo de fuerzas. Además, el dipolo de fuerzas ejerce un cizalle en el fluido, el que puede traducirse en una viscosidad activa cuando se impone un flujo externo. Esta contribución puede llegar a ser tal que la viscosidad total es nula o incluso negativa, como se ha encontrado experimentalmente. Los nadadores presentan interacciones de corto y largo alcance. En el regimen semi-diluido, las concentraciones siguen siendo bajas, pero suficientemente altas para que las interacciones de corto alcance sean relevantes sin que las de largo alcance jueguen un rol fundamental. Estas interacciones se traducen principalmente en un alineamiento entre bacterias cercanas debido a efectos estéricos e hidrodinámicos. En esta tesis se extiende la teoría cinética de suspensiones bacterianas en el régimen dilu- ido, considerando interacciones de corto alcance a través de una integral colisional. Se presen- tan dos tipos de interacciones: alineamiento polar y nemático. A partir de la ecuación cinética es posible obtener las ecuaciones hidrodinámicas de la densidad, la orientación promedio y el tensor nemático cuando existe un flujo impuesto. En particular, en esta tesis se estudia el caso de un flujo de corte uniforme. Para sistemas homogéneos se encontró que por sobre cierta concentración crítica, existe una transición hacia una fase polar o nemática, según el tipo de interacción. Ambas fases dan origen a una viscosidad oscilante en el tiempo. A través de un análisis de separación de escalas, cercano a la concentración crítica, se obtienen expresiones analíticas para la orientación promedio y el cizalle producido por una suspensión. Resultados numéricos revelan, además, que para grandes tasas de corte la fase ordenada se pierde. En particular, para colisiones nemáticas, esta fase se pierde de manera subcrítica. Finalmente se estudió la dependencia espacial de la suspensión bacteriana. A través de simulaciones tipo DSMC (Direct Simulation Monte Carlo) se resolvió la ecuación cinética condiciones de borde rígidas, encontrando estructuras espaciales en la suspensión bacteriana. El mismo fenómeno se encuentra al emplear condiciones de borde periódicas, por lo que se analizó la estabilidad lineal de la solución homogénea al ser perturbada con ondas planas. Los resultados indican que la inestabilidad ocurre para grandes longitudes de onda, por lo que es posible mediarla a través del tamaño del sistema. Además, al incluir interacciones de largo alcance al análisis de estabilidad, se obtienen que estas sólo modifican cuantitativamente los resultados. Finalmente, este fenómeno también se encontró en tres dimensiones.
Este trabajo ha sido financiado por CONICYT
30
Kotzé, Reinhardt. "Rheological characterisation of highly concentrated mineral suspensions using an ultrasonic velocity profiler /." [S.l. : s.n.], 2007. http://dk.cput.ac.za/cgi/viewcontent.cgi?article=1037&context=td_cput.
Full text
31
Wu, Jingshu. "Direct simulation of flexible particle suspensions using lattice-boltzmann equation with external boundary force." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33858.
Full textAbstract:
Determination of the relation between the bulk or rheological properties of a particle suspension and its microscopic structure is an old and important problem in physical science. In general, the rheology of particle suspension is quite complex, and the problem becomes even more complicated if the suspending particle is deformable. Despite these difficulties, a large number of theoretical and experimental investigations have been devoted to the analysis and prediction of the rheological behavior of particle suspensions. However, among these studies there are very few investigations that focus on the role of particle deformability.
A novel method for full coupling of the fluid-solid phases with sub-grid accuracy for the solid phase is developed. In this method, the flow is computed on a fixed regular 'lattice' using the lattice Boltzmann method (LBM), where each solid particle, or fiber, is mapped onto a Lagrangian frame moving continuously through the domain. The motion and orientation of the particle are obtained from Newtonian dynamics equations. The deformable particle is modeled by the lattice-spring model (LSM).The fiber deformation is calculated by an efficient flexible fiber model. The no-slip boundary condition at the fluid-solid interface is based on the external boundary force (EBF) method. This method is validated by comparing with known experimental and theoretical results.
The fiber simulation results show that the rheological properties of flexible fiber suspension are highly dependent on the microstructural characteristics of the suspension. It is shown that fiber stiffness (bending ratio BR) has strong impact on the suspension rheology in the range BR < 3. The relative viscosity of the fiber suspension under shear increases significantly as BR decreases. Direct numerical simulation of flexible fiber suspension allows computation of the primary normal stress difference as a function of BR. These results show that the primary normal stress difference has a minimum value at BR ∼ 1. The primary normal stress differences for slightly deformable fibers reaches a minimum and increases significantly as BR decreases below 1. The results are explained based on the Batchelor's relation for non-Brownian suspensions. The influence of fiber stiffness on the fiber orientation distribution and orbit constant is the major contributor to the variation in rheological properties. A least-squares curve-fitting relation for the relative viscosity is obtained for flexible fiber suspension. This relation can be used to predict the relative viscosity of flexible fiber suspension based on the result of rigid fiber suspension.
The unique capability of the LBM-EBF method for sub-grid resolution and multiscale analysis of particle suspension is applied to the challenging problem of platelet motion in blood flow. By computing the stress distribution over the platelet, the "blood damage index" is computed and compared with experiments in channels with various geometries [43]. In platelet simulation, the effect of 3D channel geometry on the platelet activation and aggregation is modeled by using LBM-EBF method. Comparison of our simulations with Fallon's experiments [43] shows a similar pattern, and shows that Dumont's BDI model [40] is more appropriate for blood damage investigation. It has been shown that channels with sharp transition geometry will have larger recirculation areas with high BDI values. By investigating the effect of hinge area geometry on BDI value, we intend to use this multiscale computational method to optimize the design of Bileaflet mechanical heart valves.
Both fiber simulations and platelet simulations have shown that the novel LBM-EBF method is more efficient and stable compare to the conventional numerical methods. The new EBF method is a two-Cway coupling method with sub-grid accuracy which makes the platelet simulations possible. The LBM-EBF is the only method to date, to the best of author's knowledge, that can simulate suspensions with large number of deformable particles under complex flow conditions. It is hoped that future researchers may benefit from this new method and the algorithms developed here.
32
Hallbom, Donald John. "Pipe flow of homogeneous slurry." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2399.
Full textAbstract:
The objective of this Thesis is to devise a system for the "rheology-based design" of non-settling (homogeneous) slurry pipelines that is more conducive to application by practicing engineers without impairing its accuracy or utility for research purposes. The cornerstone is the development of a new rheological model and constitutive equation for homogeneous slurry based on the aggregation/deaggregation of the suspended mineral particles. This “yield plastic” model is shown to describe a family of models that includes the Newtonian, Bingham plastic and Casson models as special cases. It also closely approximates the results of many consistency models, including power law, yield power law, Cross and Carreau-Yasuda.
The yield plastic model is then used to develop design equations to determine the pressure-gradient of laminar and turbulent pipe flow. A relative energy dissipation criterion is proposed for the laminar-turbulent transition and shown to be consistent with currently used transition models for Newtonian and Bingham fluids. Finally, a new dimensionless group (the “stress number”) is proposed that is directly proportional to the pressure-gradient and independent of the velocity. When the design equations are presented graphically in terms of the stress number and the plastic Reynolds number, the resulting “design curve diagram” is shown to be a dimensionless (pressure-gradient vs. velocity) pipe flow curve.
The net result is that the hydraulic design of homogeneous slurry systems only requires the use of a single constitutive equation and three engineering design equations. The results are presented in a conceptually easy form that will foster an intuitive understanding of non-Newtonian pipe flow. This will assist engineers to understand the impact of slurry rheology when designing, operating and troubleshooting slurry pipelines and, in the future, other slurry related processes.
33
Han, Long. "Study of the rheological properties of Nomex fibrids." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2205.
Full textAbstract:
Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains ix, 110 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 54-59).
34
Andrew, Chryss, and andrew chryss@rmit edu au. "Pipeline Transport of Coarse Mineral Suspensions Displaying Shear Thickening." RMIT University. Civil, Environmental and Chemical Engineering, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20081127.112225.
Full textAbstract:
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.
35
Choudhury, Tahsin Hassan. "The development of an experimental piece of equipment to monitor the sedimentation of suspensions." Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/7556.
Full text
36
Wallevik, Jon Elvar. "Rheology of Particle Suspensions : Fresh Concrete, Mortar and Cement Paste with Various Types of Lignosulfonates." Doctoral thesis, Norwegian University of Science and Technology, Department of Structural Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-319.
Full textAbstract:
The major issue concerns how the different lignosulfonate types changes the rheological properties of the cement based material (concrete, mortar and cement paste) as a function of temperature and time. In such terms, it is demonstrated that the high molecular weight lignosulfonates performs far better than the low molecular weight ones. The former type also performs considerable better compared to a naphthalene based polymer.
The above investigation is done with help from the second part of this thesis, which identifies some of the parameters p1, p2,... affecting the shear viscosity η = η ( p1, p2,...) of the cement based material. This is done by investigating the thixotropic behavior of cement paste mixed with either lignosulfonates or naphthalene. The thixotropic behavior is directly related to coagulation, dispersion and re-coagulation of the cement particles. In making the analysis, a modification is applied to the Hattori-Izumi theory, which is a theory about the bookkeeping of the number of reversible coagulated connections between the cement particles. The modification consist, among other things, of include a fading memory to the analysis. That is, the cement paste is allowed to remember its recent past. By a combination of experimental results and numerical simulations, it is demonstrated that such memory term is very important.
An experimental error is present during a viscometric measurement on concrete (a coaxial cylinders viscometer is used). The error is generated by particle migration. Investigating and compensating for this error constitutes the third part of this thesis. Realizing the nature of this error, some corrections are applied. However, with these corrections, one is only extracting the viscometric values of a "fat'' concrete that surrounds the inner cylinder of the viscometer after the particle migration is basically complete, and not of the concrete in the original homogenous state.
37
Bossler, Frank [Verfasser], and E. [Akademischer Betreuer] Koos. "Structural Investigations of Capillary Suspensions using Rheology and Confocal Microscopy / Frank Bossler ; Betreuer: E. Koos." Karlsruhe : KIT-Bibliothek, 2018. http://d-nb.info/116254080X/34.
Full text
38
Agarwal, Neeraj. "Transient Shear Flow Rheology of Concentrated Long Glass Fiber Suspensions in a Sliding Plate Rheometer." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/34784.
Full textAbstract:
Transient viscosity growth measurements at the startup of shear flow were performed on long glass fiber-filled polypropylene. Samples were prepared with fibers pre-oriented either in 1-direction, 3-direction or random in 1-3 plane, where the 1-direction is the direction of shear motion, the 2-direction is perpendicular to the shear plane and the 3-direction is the neutral direction. A sliding plate rheometer incorporating a shear stress transducer was constructed in the lab. It was shown that this device works well for the tested materials including a Newtonian oil, a low density polyethylene (LDPE) and short glass fiber-filled polypropylene. The transient viscosity growth behavior for long glass fiber suspensions was subsequently investigated. The results suggested that both, fiber length and fiber concentration have pronounced effect on the steady state suspension viscosity. It was also observed that the transient behavior of the pre-oriented samples was highly dependent on the initial orientation state of the fibers.Master of Science
39
Fusier, Jennifer. "Suspensions floculées modèles : de la caractérisation à la modélisation." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1114/document.
Full textAbstract:
Les suspensions de particules colloidales dans des fluides newtoniens sont utilisées dans un grand nombre de secteurs pour leurs propriétés complexes. Ces dernières proviennent de l’interaction entre les forces hydrodynamiques et les forces physico-chimiques interparticulaires. Malgré de nombreuses études dédiées aux comportements des suspensions colloïdales le lien entre propriétés macroscopiques et forces d’interactions est toujours source de discussions. L’objectif de ce travail est de comprendre et caractériser, aux différentes échelles, et à l’aide de différentes techniques expérimentales, le lien entre la floculation des suspensions et quelques grandeurs rhéologiques (module élastique et contrainte seuil) caractérisant leur comportement macroscopique.La diversité chimique, en taille et en forme des constituants des pâtes cimentaires ainsi que la réactivité du système rendant l’étude trop délicate, des suspensions modèles sont utilisées (particules de silice sphériques et broyés en suspension dans de l’eau).Les suspensions colloïdales formulées sont thixotropes, l’évolution des propriétés rhéologiques en fonction du temps est analysée.Pour les deux types de suspensions, on observe que la contrainte seuil et le module élastique augmentent avec la fraction volumique en particules, la force ionique et le temps de repos.Ces deux grandeurs dépendent de la microstructure des suspensions mais décrivent deux réponses distinctes du matériau suite à l’application d’une sollicitation mécanique. Bien que ces grandeurs soient pilotées par la microstructure du matériau il n’y a pas d’évidence qu’elles soient liées l’une à l’autre. Cependant toutes les données G’=f(Tc) se placent sur une courbe unique pour un type de particule et une taille donnée. Ce résultat confirme que le module élastique peut être utilisé comme un paramètre de structuration caractérisant l’influence de la floculation sur la contrainte seuil. De plus nous nous sommes intéressés à l’impact de la taille des particules sur la réponse rhéologique du matériau. Nous observons que la contrainte seuil est proportionnelle à l’inverse de la taille des particules au carré et le module élastique à l’inverse de la taille des particules. Les modèles présents dans la littérature ne prédisent pas la même normalisation par la taille, cela suggère que les interactions interparticulaires contrôlant le comportement macroscopique ne sont pas encore totalement comprises.L’observation des suspensions au repos par microscopie confocale ne révèle pas de réorganisation structurelle dans le temps. Ainsi la thixotropie des suspensions s’explique probablement par l’existence de nano-organisations structurelles. Cependant des différences de structures sont mises en évidence pour des suspensions de formulations éloignées. Une structure primaire dépendant de l’intensité des interactions et de la fraction volumique se forme de manière instantanée une fois que le précisaillement est arrêté. Il s’en suit une évolution des propriétés rhéologiques avec le temps de repos qui est attribuée à des réarrangements très localisés non visibles par microscopieSuspensions of colloidal particles suspended in a Newtonian fluid are encountered in many fields of daily life or industrial sectors. Complex behavior of colloidal suspensions comes from the interplay between hydrodynamical and several physico-chemical interactions between the particles. Even if a lot of works have been devoted to these topics, the complex relationships between the interparticle forces and the suspension's overall macroscopic behavior are far from being fully understood. This work aims to understand and characterize, at different scales, and through several techniques, the link between the flocculation state and some rheological properties (elastic modulus and yield stress) of colloidal suspensions.As in real system diversity in sizes, shapes, chemical constituents combined with chemical reaction make the system hard to control we work with model suspensions (spherical and crushed silica particles suspended in water).The suspensions being highly thixotropic, we characterize the evolution of their rheological properties (elastic modulus: G’ and yield stress: τc) with time.We observe for both materials that yield stress and elastic modulus increase with volume fraction, ionic strength and resting time.The two quantities G’ and τc depend on the microstructure ie the floculation state but are linked to two different kinds of response when a mechanical loading is apply to the system. Of course, both quantities depend on the flocculation state of the system but there is not clear evidence that these two quantities must be linked one to the other. However all the data G’=f (τc) collapse onto a simple curve for a given type and a given size of particle. This result proves that elastic shear modulus can be used as a “structural parameter” to account for the influence of flocculation on the yield stress.Moreover we focus on the effect of particle size on the measured properties and we observe that the yield stress scales with the inverse of the squared particle size and the elastic modulus with the inverse of particle size. The models existing in literature do not predict this scaling which would suggest that the interactions controlling macroscopic behaviour are still not fully understood.The observations performed with cofocal microscopy do not reveal any structural organisations when suspensions are left at rest. Then thixotropy of suspensions is assumed to be linked to nano scale change in microstructure. But different microstructure are observed regarding the suspension formulation. A primary microstructure is instantaneously formed once preshear is stopped depending on the intensity of interactions and volume fraction. After that the evolution of rheometric quantities with resting time are attributed to very local rearrangement not detectable with microscopy
40
Miller, Ryan Michael. "Continuum Modeling of Liquid-Solid Suspensions for Nonviscometric Flows." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4864.
Full textAbstract:
A suspension flow model based on the "suspension balance" approach has been developed. This work modifies the model to allow the solution of suspension flows under general flow conditions. This requires the development of a frame-invariant constitutive model for the particle stress which can take into account the spatially-varying local kinematic conditions. The mass and momentum balances for the bulk suspension
and particle phase are solved numerically using a finite volume method. The particle stress is based upon the computed rate of strain and the local kinematic conditions. A nonlocal stress
contribution corrects the continuum approximation of the particle phase for finite particle size effects. Local kinematic conditions are accounted through the local ratio of rotation to extension in the flow field. The coordinates for the stress definition are the local principal axes of the rate of strain field.
The developed model is applied to a range of problems. (i) Axially-developing conduit flows are computed using both the full two-dimensional solution and the more computationally
efficient "marching" method. The model predictions are compared to experimental results for cross-stream particle concentration profiles and axial development lengths. (ii) Model
predictions are compared to experiments for wide-gap circular Couette flow of a concentrated suspension in a shear-thinning liquid. With minor modification, the suspension flow model predicts the major trends and results observed in this flow. (iii) Comparisons are made to experiments for an axisymmetric contraction-expansion. Model predictions for a two-dimensional planar contraction flow test the influence of model formulation. The variation of the magnitude of an isotropic particle normal stress with local kinematic conditions and anisotropy in the
in-plane normal stresses are both explored. The formulation of the particle phase stress is found to have significant effects on the solid fraction and velocity. (iv) Finally, for a rectangular
piston-driven flow and an obstructed channel flow, a "computational suspension dynamics" study explores the effect of particle migration on the bulk flow field, system pressure drop
and particle phase composition.
41
Chou, Yi-Ping. "Improving the strength of ceramics by controlling the interparticle forces and rheology of the ceramic suspensions." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248369.
Full text
42
Dabak, Turgay. "Formulation of the particle size distribution effects on the rheology and hydraulics of highly-concentrated suspensions." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/74729.
Full textAbstract:
A formulation was developed for the rheological characterization of highly concentrated suspensions, accounting for the physical effects of particle size distribution. A number of dimensionless parameters were developed signifying the physical characteristics of the solids and the vehicle fluid, and functionally related to the yield-stress and a flow parameter. Each of these expressions of the formulation contains an empirical dimensionless coefficient accounting for the interparticle and fluid/solid interactions that are not explained by the physical parameters involved. A formulation and a methodology were also developed for predicting the shear viscosity behavior of highly concentrated suspensions at low and high shear-rates through the use of three parameters signifying effects of particle size distribution. A number of applications were made using various non-coal and limited coal-liquid mixture data reported in the literature to demonstrate the general validity of the formulations.
A methodology was proposed for the analysis of the particle size distribution effects on the overall optimum energy efficiency during hydraulic transportation and particle size reduction. The computer model developed for this purpose was employed to evaluate the transportation energy consumption and the energy consumed in the grinding process to prepare the slurry, in pipes of various sizes and lengths for a coal slurry of various specified particle size distributions and concentrations. Correlations obtained indicated the sensitivity of transportation energy efficiency to various parameters including the maximum packing concentration, relative concentration, specific surface area of particles, surface area mean size, pipe size and length, and annual mixture throughput. The results of combined energy calculations have shown that the particle size distribution and related physical parameters can significantly affect the energy efficiency due to both grinding and transportation, and the delivered cost of slurry fuels.Ph. D.
43
Lim, Amanda Seet Hwa. "Implementing the split Hopkinson pressure bar technique for complex fluid evaluation." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 252 p, 2010. http://proquest.umi.com/pqdweb?did=1992504671&sid=8&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text
44
Vu, Thai Son. "Rhéologie des suspensions non newtoniennes." Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00598310.
Full textAbstract:
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
45
Egres, Ronald G. Jr. "The effects of particle anisotropy on the rheology and microstructure of concentrated colloidal suspensions through the shear thickening transition." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 12.78 Mb., 263 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3200542.
Full text
46
Kessler, Christopher S. "Freeze Casting of Aqueous PAA-Stabilized Carbon Nanotube-Al2O3 Suspensions." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/44137.
Full textAbstract:
Freeze casting is a colloidal processing technique that shows great promise for development of nanostructured materials. A ceramic nanopowder is dispersed with a polymer in water, under carefully controlled pH. The suspension is cast into a suitable mold and frozen, then de-molded and exposed to a vacuum to sublimate and remove the water. Polymer adsorption and rheology were studied to optimize and characterize a colloidal suspension of a 38 nm Al2O3 powder. The dispersant, dispersant amount, pH and solids loading were examined to determine the best conditions for freeze casting. Based on adsorption and viscosity data, optimal conditions for freeze casting were found with Poly(acrylic acid) (PAA) dispersant, at 2.00 wt% (of Al2O3), pH of 9.5, and a solids loading of 40 vol%. Carbon nanotubes (CNTs) were added to that suspension in increments of 0.14, 0.28, 0.53, 1.30 and 2.60 vol%. The viscosity increased dramatically upon addition of 1.30 vol% CNTs. The colloidal CNT-Al2O3 suspension was successfully freeze cast and the microstructure showed a very smooth fracture surface. It was determined that upon resting, the suspension undergoes a physical change which must be completed to obtain advantageous microstructure. Freeze cast Al2O3 discs with and without CNTs were measured using a concentric ring test, with strengths on the order of one MPa. The freeze cast sample was successfully debinded, but the heating profile attempted was not effective in obtaining full density.Master of Science
47
Pfeiff, Carlos. "Dépendance de la traînée d'obstacles cylindriques de la rhéologie de suspensions aqueuses concentrées." Grenoble 1, 1986. http://www.theses.fr/1986GRE10093.
Full textAbstract:
Etude experimentale a l'aide de plusieurs types de viscosimetres. On degage un modele semi-empirique pour l'estimation du seuil de contraintes et de la viscosite apparente. Mesure de la trainee exercee sur des obstacles cylindriques. Etude de l'influence du rapport d'elancement et de la presence des parois laterales.
48
Kagarise, Christopher D. "Rheological Characterization and Modeling of Micro- and Nano-Scale Particle Suspensions." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1259699454.
Full text
49
Fan, Zhihang. "Flow and rheology of multi-walled carbon nanotubes thermoset resin suspensions in processing of glass fiber composites." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 254 p, 2007. http://proquest.umi.com/pqdweb?did=1362534231&sid=8&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text
50
Vernier, Frederic C. "Influence of emulsifiers on the rheology of chocolate and suspensions of cocoa or sugar particles in oil." Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503471.
Full textAbstract:
Rheological measurements were conducted on samples of chocolate containing various lecithin fictions and lipid sources in order to find a replacement for PGPR, a yield value reducing synthetic emulsifier. Only the oats extract was found to provide the desired reduction in yield value. together with a reduction in plastic viscosity similar to lecithin. Synthetic surfactants bearing various structural characteristics were investigated for their ability to reduce the yield value of chocolate. The best performances were obtained for emulsifiers with long tail groups, such as polymerised fatty acids or long chain hydrocarbons. Polglycerol esters of fatty acids of low HLB provided an excellent yield value reducing ability. Strong interaction of the surfactant head group with the sugar surfaces (mostly by hydrogen bonding) was found to be crucial for effective yield value reduction. Visualisation of lecithin and P(1PR in a sugar in oil suspension (a model of chocolate) was achieved. Both emulsifiers were localised at the interface between sugar and oil, and lecithin was found to displace some of the PGPR from the interface. Solvent extraction experiments were conducted on sugar in oil suspensions containing lecithin, PGPR, an oats extract and a mixture of lecithin and PGPR. SAXS and SANS work conducted suggested that while free PGPR has no impact on the rheological properties of a sugar in oil suspension once a critical concentration corresponding to a yield value minimum had been reached, free lecithin contributed to the formation of loose multilayers between sugar particles, resulting in increased yield value. The influence of various emulsifiers on the rheological properties of cocoa suspensions was also investigated. Lecithin and PGPR showed a similar effects on the yield values to what was observed in the case of sugar in oil dispersions. However, the oats extract was found to have virtually no surface active effect, probably due to poor interactions of its surface active glycolipid with the cocoa particle surfaces