Magnetic resonance (MR) is a highly versatile technique with great potential for use in industrial applications; from the in situ study of unit operations to the optimisation of product properties. This thesis, concerned with the latter, is divided into two parts. Firstly, dynamic MR is applied to characterise the flow behaviour, or rheology, of process fluids. Such characterisation is typically performed using conventional rheometry methods operating offline, with an online, or inline, method sought for process control and optimisation. Until recently, MR was an unlikely choice for this application due to the requirement of high-field MR hardware. However, recent developments in low-field MR hardware mean that the potential of MR in such applications can now be realised. Since the implementation of MR flow imaging is challenging on low-field MR hardware, two new approaches to MR rheometry are described using pulsed field gradient (PFG) MR. A cumulant analysis of the PFG MR signal is first used to characterise the rheology of model power-law fluids, namely xanthan gum-in-water solutions, accurate to within 5% of conventional rheometry, the data being acquired in only 6% of the time required when using MR flow imaging. The second approach utilises a Bayesian analysis of the PFG MR signal to characterise the rheology of model Herschel--Bulkley fluids, namely Carbopol 940-in-water solutions; data are acquired in only 12% of the time required for analysis using MR flow imaging. The suitability of the Bayesian MR approach to study process fluids is demonstrated through experimental study on an alumina-in-acetic acid slurry used by Johnson Matthey. Secondly, MR imaging is used to provide insights into the origins and mechanisms of colloidal gel collapse. Many industrial products are colloidal gels, a space-spanning network of attractive particles with a yield stress. Colloidal gels are, however, known to undergo gravitational collapse after a latency period, thus limiting the shelf-life of products. This remains poorly understood, with a more detailed understanding of both fundamental interest and practical importance. To this end, MR imaging is applied offline to investigate the phase behaviour of colloidal gels. In particular, a comparison of the simulated and experimental phase diagrams suggests gravitational gel collapse to be gravity-driven. Furthermore, measurement of the colloid volume fraction using MR imaging indicates the formation of clusters of colloids at the top of the samples. Whether such clusters initiate gravitational gel collapse is yield stress-dependent; the gravitational stress exerted by a cluster must be sufficient to yield the colloidal gel.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2011. / Despite the extensive research work carried out on flow through short square-edged orifice plates over the last century (e.g. Johansen, 1930; Benedict, 1977; Alvi et al., 1978; Swamee, 2005; ESDU, 2007), gaps in the engineering data still exist for certain ranges of flow conditions and geometries. The majority of data available in the literature are for Newtonian fluids in the turbulent flow regime (ESDU, 2007). Insufficient data have been observed for the orifice with pipe diameter ratio, β = 0.2, in the laminar flow regime. There are no experimental data for β = 0.3 and 0.57. The objective of this thesis was to conduct wide-ranging experimental studies of the flow in orifice plates, which included those geometrical configurations, by measuring pressure loss coefficients and discharge coefficients across the orifice plates using both Newtonian fluids and non-Newtonian fluids in both laminar and turbulent flow regimes. The test work was conducted on the valve test rig at the Cape Peninsula University of Technology. Four classical circular short square-edged orifice plates having, β = 0.2, 0.3, 0.57 and 0.7, were tested. In addition, two generation 0 Von Koch orifice plates (Von Koch, 1904), with equivalent cross sectional area were also tested for β = 0.57. Water was used as Newtonian fluid to obtain turbulent regime data and also for calibration purposes to ensure measurement accuracy and carboxymethyl cellulose, bentonite and kaolin slurries were used at different concentrations to obtain laminar and transitional loss coefficient data. The hydraulic grade line method was used to evaluate pressure loss coefficients (Edwards et al., 1985), while the flange tap arrangement method was used to determine the discharge coefficients (ESDU, 2007). A tube viscometer with three different pipe diameters was used to obtain the rheological properties of the fluids. The results for each test are presented in the form of pressure loss coefficient (kor) and discharge coefficient (Cd) against pipe Reynolds number (Re)

Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2013 / The flow of reactive viscous fluids in porous media presents a theoretically challenging problem and has a broad range of scientific, technological and engineering applications. Real life areas where such flow systems are encountered include drying of food, geothermal energy extraction, nuclear waste disposal, the flow of heat and fluid inside human organs, insulation of buildings, groundwater movement, oil and gas production, astrophysical plasmas, magnetohydrodynamic (MHD) pumps and generators, metal extraction and granulation of metals, aerospace and ship propulsion and automobile exhaust systems. The reactions within such flow systems are inherently exothermic. It is in this view that we carry out studies of thermal effects and thermal stability criteria for unsteady flows of reactive variable viscosity non-Newtonian fluids through saturated porous media. The study focuses on non-Newtonian fluids mainly because the majority of industrial fluids exhibit non-Newtonian character. Particular focus will be on fluids of the differential type exemplified by third grade fluid. Both analytical and numerical techniques were employed to solve the nonlinear partial differential equations that were derived from the conservation principles, namely the principles of conservation of mass, momentum and energy balance. Graphical representations were adopted in trying to explain the response of solutions to various flow parameter variations. In chapter 1 we defined important terms and expressions, laid down a summary of important applications, carried out literature survey, stated the statement of the problem, the aims and objectives of the study as well as an outline of the envisaged research methodology. Chapter 2 focuses on the derivations of the fundamental equations that derive the flow system. These are the continuity equation, the momentum equation and the energy equation. In chapter 3 we computationally investigated the unsteady flow of a reactive temperature dependent viscosity third grade fluid through a porous saturated medium with asymmetric convective boundary conditions. The response of velocity and temperature fields to each of the various flow parameters was analysed and interpreted. A transient increase in both the velocity and temperature profiles with an increase in the reaction strength, viscous heating and fluid viscosity parameter was observed. On the other hand, a transient decrease in the field properties was observed with increase in non-Newtonian character and the porous medium shape parameter. The reaction was noticed to blow-up if, depending on other flow parameters, the reaction strength is not carefully controlled.

O estudo do comportamento reológico de fluidos não Newtonianos tem grande importância em diversas áreas da engenharia. O aumento na demanda destes fluidos por exemplo, no uso doméstico, pessoal e em processos químicos acarreta em dificuldades que vão desde o processo de sua mistura ao seu manuseio. Dentre os fluidos não Newtonianos estão os viscoelásticos, os quais exibem deformação aparente quando os níveis de tensões são inferiores ao limite de escoamento do material e, dentro desta classe, alguns ainda podem apresentam comportamento elástico quando submetidos à baixa taxa de cisalhamento. Juntamente com os efeitos elasto-viscoplásticos, os materiais podem apresentar comportamento tixotrópico, onde devido as tensões sua reestruturação não é instantânea. Na presente Tese, fez-se um estudo numérico a fim de analisar o problema especifico de escoamentos de fluidos elasto-viscoplásticos com comportamento tixotrópico em uma expansão planar abrupta na razão de aspecto 4 : 1. O modelo mecânico aplicado consiste de uma equação viscoelástica para o campo de tensões, uma evolutiva para o parâmetro de estrutura do material, bem como as equações de conservação de massa e momento. O modelo mecânico aplicado mostrou-se capaz de prever o comportamento tixotrópico. A aproximação numérica do modelo aplicado foi feita através do método estabilizado de elementos finitos, especificamente o método Galerkin Mínimos-Quadrados (GLS), o qual foi implementado no código de elementos finitos para fluidos não Newtonianos em desenvolvimento no Laboratório de Mecânica dos Fluidos Aplicada e Computacional (LAMAC) da Universidade Federal do Rio Grande do Sul. Os fenômenos reológicos presentes no problema foram analisados a partir da influência da cinemática do escoamento, da elasticidade e da tixotropia, no nível de estruturação do material, na posição e tamanho das regiões não escoadas e na deformação elástica do material. Os resultados mostraram-se satisfatórios, pois condizem com os apresentados na literatura, apontando a boa predição do modelo mecânico aplicado bem como a robustez de sua implementação computacional. / The rheological behavior of non-Newtonian uids study is of great then importance in many areas of engineering. The increase in demand of these uids - for example, domestic use, personal and processes chemical - causes di culties ranging from the process of mixing it to handling. Among the non-Newtonian uids are viscoelastic, which exhibit apparent deformation when stress levels are lower than the yield limit of the material and, within this class, some still have elastic behavior when subjected to low shear rates. Together with the elastic-viscoplastic e ects, materials may exhibit thixotropic behavior, ie, due the restructuring strain is not instantaneous. In this thesis was made a numerical study to simulate the speci c problem of ow of elastic-viscoplastic uids with thixotropic behavior in abrupt planar expansion { common geometry in industrial systems associated with elastic-viscoplastic uids, whose ratio the aspect is 4:1. The mechanical behavior of most of these structured materials, are highly non-Newtonian, with this, there is need to make them more pseudoplastic, causing undesirable behaviors such as thixotropic which is a phenomenon somewhat characterized and modeled in the literature. The mechanical model applied is able to predict thixotropic behavior and is composed of a viscoelastic equation for the stress eld and an evolutionary to the material structure parameter in addition to the mass and momentum conservation equations. This mechanical model is approximated by a stabilized nite element model, called the Galerkin method of least squares (GLS). In order to study the rheological phenomena present in the problem is analyzed the in uence of the ow kinematics, elasticity and thixotropy in the level of structure of the material, in position and size of unyielded regions and the elastic deformation of the material. The results were satisfactory, since the the study of intensity the U the results agree with those reported in the literature pointing to good prediction of the mechanical model applied well as the hardiness of their computational implementation.The results of the elasticity showed quite spectacular behavior of unyielded regions of the material since for high values of relaxation time, the unyielded region of channel larger has the form of " ngers"because of the high exibility of the material along the line of symmetry of the channel. The results of the analysis of the elastic deformation show, that model correctly dosing the elasticity in the unyielded regions. The thixotropic e ects reported a slower structuring of the material with increasing characteristic time, in response to strain change caused by the expansion, results indicate that for high values of relaxation time, higher the distance between the unyielded regions of smaller channel and larger.

O estudo do comportamento reológico de fluidos não Newtonianos tem grande importância em diversas áreas da engenharia. O aumento na demanda destes fluidos por exemplo, no uso doméstico, pessoal e em processos químicos acarreta em dificuldades que vão desde o processo de sua mistura ao seu manuseio. Dentre os fluidos não Newtonianos estão os viscoelásticos, os quais exibem deformação aparente quando os níveis de tensões são inferiores ao limite de escoamento do material e, dentro desta classe, alguns ainda podem apresentam comportamento elástico quando submetidos à baixa taxa de cisalhamento. Juntamente com os efeitos elasto-viscoplásticos, os materiais podem apresentar comportamento tixotrópico, onde devido as tensões sua reestruturação não é instantânea. Na presente Tese, fez-se um estudo numérico a fim de analisar o problema especifico de escoamentos de fluidos elasto-viscoplásticos com comportamento tixotrópico em uma expansão planar abrupta na razão de aspecto 4 : 1. O modelo mecânico aplicado consiste de uma equação viscoelástica para o campo de tensões, uma evolutiva para o parâmetro de estrutura do material, bem como as equações de conservação de massa e momento. O modelo mecânico aplicado mostrou-se capaz de prever o comportamento tixotrópico. A aproximação numérica do modelo aplicado foi feita através do método estabilizado de elementos finitos, especificamente o método Galerkin Mínimos-Quadrados (GLS), o qual foi implementado no código de elementos finitos para fluidos não Newtonianos em desenvolvimento no Laboratório de Mecânica dos Fluidos Aplicada e Computacional (LAMAC) da Universidade Federal do Rio Grande do Sul. Os fenômenos reológicos presentes no problema foram analisados a partir da influência da cinemática do escoamento, da elasticidade e da tixotropia, no nível de estruturação do material, na posição e tamanho das regiões não escoadas e na deformação elástica do material. Os resultados mostraram-se satisfatórios, pois condizem com os apresentados na literatura, apontando a boa predição do modelo mecânico aplicado bem como a robustez de sua implementação computacional. / The rheological behavior of non-Newtonian uids study is of great then importance in many areas of engineering. The increase in demand of these uids - for example, domestic use, personal and processes chemical - causes di culties ranging from the process of mixing it to handling. Among the non-Newtonian uids are viscoelastic, which exhibit apparent deformation when stress levels are lower than the yield limit of the material and, within this class, some still have elastic behavior when subjected to low shear rates. Together with the elastic-viscoplastic e ects, materials may exhibit thixotropic behavior, ie, due the restructuring strain is not instantaneous. In this thesis was made a numerical study to simulate the speci c problem of ow of elastic-viscoplastic uids with thixotropic behavior in abrupt planar expansion { common geometry in industrial systems associated with elastic-viscoplastic uids, whose ratio the aspect is 4:1. The mechanical behavior of most of these structured materials, are highly non-Newtonian, with this, there is need to make them more pseudoplastic, causing undesirable behaviors such as thixotropic which is a phenomenon somewhat characterized and modeled in the literature. The mechanical model applied is able to predict thixotropic behavior and is composed of a viscoelastic equation for the stress eld and an evolutionary to the material structure parameter in addition to the mass and momentum conservation equations. This mechanical model is approximated by a stabilized nite element model, called the Galerkin method of least squares (GLS). In order to study the rheological phenomena present in the problem is analyzed the in uence of the ow kinematics, elasticity and thixotropy in the level of structure of the material, in position and size of unyielded regions and the elastic deformation of the material. The results were satisfactory, since the the study of intensity the U the results agree with those reported in the literature pointing to good prediction of the mechanical model applied well as the hardiness of their computational implementation.The results of the elasticity showed quite spectacular behavior of unyielded regions of the material since for high values of relaxation time, the unyielded region of channel larger has the form of " ngers"because of the high exibility of the material along the line of symmetry of the channel. The results of the analysis of the elastic deformation show, that model correctly dosing the elasticity in the unyielded regions. The thixotropic e ects reported a slower structuring of the material with increasing characteristic time, in response to strain change caused by the expansion, results indicate that for high values of relaxation time, higher the distance between the unyielded regions of smaller channel and larger.

Orientadores: Vivaldo Silveira Junior, Javier Telis Romero / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-06T15:00:42Z (GMT). No. of bitstreams: 1 Gratao_AnaCarolinaAmaral_D.pdf: 2034155 bytes, checksum: 7a7cc4a961cab6b38ae3dc5ee5f3f9d8 (MD5) Previous issue date: 2006 / Doutorado / Engenharia de Alimentos / Doutor em Engenharia de Alimentos

Orientador: Marcelo Martins dos Santos / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-18T21:33:13Z (GMT). No. of bitstreams: 1 Dias_GilberlandioJesus_D.pdf: 729241 bytes, checksum: 697941f5eb00690299a087d1432b35cf (MD5) Previous issue date: 2011 / Resumo: Neste trabalho estudamos o escoamento de fluidos viscosos não Newtonianos, modelados pelo sistema estacionário incompressível de Navier-Stokes obedecendo a uma Lei de Potência, em domínios com canais infinitos. Tratamos basicamente de dois tipos de domínios: domínios com canais cuja seção transversal é limitada e domínios com canais possuindo seção transversal ilimitada. Tanto para domínios com seção transversal limitada quanto para domínios com seção transversal ilimitada, estudamos o problema proposto por Ladyzhenskaya e Solonnikov [Zap. Nauchn. Sem. Leningrad Otdel. Mat. Inst. Steklov (LOMI), 96(1980)117-160 (English Transl.: J. Soviet Math., 21, 1983, 728-761)]. Findamos nosso trabalho fazendo um estudo sobre estimativas em espaços de Sobolev com peso para soluções do sistema de Stokes com Lei de Potência / Abstract: In this work we study the flow of the viscous non-Newtonian fluids, modeled by the steady incompressible Navier-Stokes system obeying a power-law, in domains with infinite channels. We deal basically two types of domains: domains with channels whose cross section is limited and domains with channels having unlimited cross section. For both domains with limited cross section and for domains with unbounded cross section, we study the problem proposed by Ladyzhenskaya and Solonnikov [Zap. Nauchno. Sem Leningrad Otdel. Mat. Inst. Steklov (Lomi), 96 (1980) 117-160 (Portugu¿es Transl.: J. Soviet Math., 21, 1983, 728-761)]. We finished our work making a study of estimates in Sobolev weight spaces for solutions of the Stokes power-law system / Doutorado / Matematica / Doutor em Matemática

Some non-newtonian fluids exhibit nonmonotonous dependence of the shear stress on shear rate. This nonmonoticity leads to flow instabilities which result in formation of banded flow, namely in shear banding and vorticity banding. An important role is played here by so called stress diffusion which uniquely determines size of bands in the flow. If the classical kinetic approach is employed and the spatial inhomogeneity of the flow is taken into the account, then stress diffusion can be obtained in the fluid model, however this approach has difficulties with identifying heat transfer within the continuum. In this thesis, we present alternative approach how to introduce stress diffusion to fluid models. We employ thermodynamical framework proposed by Rajagopal and Srinivasa (2000), this approach guaranties thermodynamical consistency of resulting model and also the interplay between stress diffusion and heat transfer can be easily established. Furthermore, we extend this framework such that wider range of viscoelastic models can be obtained, in particular we derive Johnson-Segalman model. Powered by TCPDF (www.tcpdf.org)

[pt] O deslocamento de um líquido por outro em espaços anulares é comumente encontrado na indústria do petróleo, e a maioria deles envolve materiais não newtonianos. O espaço anular muitas vezes apresenta irregularidades causadas pela erosão, onde quantidades consideráveis de fluido de perfuração podem ser deixadas para trás durante o processo de deslocamento, comprometendo a qualidade da operação de cimentação. Motivados por esse processo industrial, testes de deslocamento entre líquidos a vazão constante foram realizados em espaços anulares cuja parede externa possui, em uma determinada posição axial, um aumento repentino de diâmetro seguido de uma diminuição repentina de diâmetro mais a jusante. O objetivo dos experimentos era determinar a eficiência do deslocamento em função da vazão, reologia dos fluidos e geometria da cavidade. Os resultados revelaram forte influência desses parâmetros na eficiência de deslocamento. Ao mesmo tempo, um estudo numérico foi desenvolvido. Simulações numéricas das equações de Navier-Stokes em geometria axissimétrica para fluidos incompressíveis foram acopladas ao método Level-Set para captura da interface. Fluidos com viscosidade constante e o modelo newtoniano generalizado com função viscosidade de Carreau-Yasuda foram utilizados. Isso permitiu simular deslocamentos entre dois fluidos newtonianos e entre um fluido newtoniano e outro não-newtoniano. Este foi utilizado tanto como fluido deslocador quanto como deslocado. Foram realizadas simulações para várias razões de diâmetros, viscosidades, tempos de relaxação, e números de capilaridade e de Reynolds. Identificamos quando a aproximação do espaço anular por duas placas paralelas pode ser aplicada e calculamos como a forma da interface depende dos parâmetros investigados. / [en] The displacement of a fluid caused by another one, inside annular spaces, is commonly found in the oil industry and most of these rearrangements involve non-Newtonian materials. The annular space often shows irregularities caused by erosion, in which considerable amounts of drilling fluid can be left behind during the displacement process, compromising the cementing operation efficiency. Motivated by that industrial process, fluid-fluid displacement tests at constant flow rate were performed in annular spaces in which their exterior walls displayed - in a determined axial position - an abrupt expansion followed by an abrupt contraction. The purpose of the tests were to determine the displacement efficiency as a function of flow rate, rheological properties and geometric cavity. The results revealed a strong influence of these parameters on the displacement efficiency. At the same time, a numerical research was developed. Numerical simulations of the Navier-Stokes equations in axisymmetric geometry for incompressible fluids were coupled to the Level-Set method to capture the interface. Fluids with constant viscosity and the generalized Newtonian model with viscosity function of Carreau-Yasuda were used. That allowed to simulate displacements between two Newtonian fluids and a Newtonian and a non-Newtonian fluid. This was used both as a displacer and as a displaced fluid. Simulations were performed for several diameters and viscosities ratios, relaxatation time, capilar and Reynolds numbers. We identified when the approximation of the annular space by two parallel plates can be applied and calculated how the shape of the interface depends on the investigated parameters.

We develop a viscoelastic version of the volume of fluid algorithm for tracking deformable interfaces. The code uses the piecewise linear interface calculation method to reconstruct the interface, the continuous surface force formulation to model interfacial tension forces and utilizes the semi-implicit Stokes solver (enabling computations at low Reynolds numbers). The algorithm is primarily designed to simulate the flow of superposed fluids and the drop in a flow problem in 2D shear flows of viscoelastic and/or Newtonian fluids. The code is validated against linear stability theory for the two-layer flow case and against experimental and other documented numerical investigations for the droplet-matrix case. / Ph. D.