[pt] Umas das etapas mais complexas e críticas durante a construção de poços de petróleo é o processo de cimentação primária, definido como: O processo de instalação de cimento no anular entre o revestimento e a formação exposta ao poço [1]. Ela fornece isolamento zonal permanente para evitar contaminação ou migração de fluidos indesejáveis no anular, protege o revestimento da ocorrência de corrosão e fornece estabilidade hidráulica e mecânica para o revestimento ao longo da vida produtiva do poço de petróleo. Neste processo, ainda na etapa de perfuração, irregularidades na seção transversal (washouts) podem ser geradas como resultado de diversos colapsos parciais da seção do poço aberto em decorrência da presença de rochas pouco consolidadas da formação. Uma operação de cimentação primária bem sucedida dependerá se o sistema de fluidos espaçadores e a pasta de cimento deslocam de forma adequada e completa o fluido de perfuração do anular e washouts. Motivados por esse problema industrial, a presente dissertação usa um simulador numérico DNS (Direct Numerical Simulation) com o objetivo de analisar sistematicamente o comportamento hidrodinâmico e calcular a eficiência do deslocamento entre dois fluidos newtonianos miscíveis através de um anular contendo uma expansão seguida de uma contração abrupta. Investigamos como diferentes viscosidades e densidades dos fluidos, um injetado e outro deslocado, a miscibilidade entre eles, a taxa de injeção e a dimensão do washout retangular afetam o escoamento bifásico. Consideramos uma geometria axissimétrica durante processos de deslocamentos verticais, e as equações governantes são resolvidas em coordenadas cilíndricas, permitindo investigar diferentes aberturas anulares. Devido à miscibilidade entre os fluidos, nossos resultados preveem eficiências de deslocamento altíssimas, próximas a 100 Fluidos não-newtonianos são usualmente utilizados durante o processo industrial de cimentação primária de poços de petróleo. Contudo, as altas eficiências de deslocamentos encontradas em nossos resultados motivam estudos futuros sobre a influência da miscibilidade em deslocamentos de fluidos complexos. Estes resultados também motivam o uso de fluidos espaçadores para tentar controlar as propriedades de interface. Desta forma, é possível que a utilização de sistemas que se aproximem das condições reológicas e hidrodinâmicas de deslocamento entre fluidos newtonianos miscíveis poderá contribuir para um aumento da eficiência de deslocamento e, consequentemente, otimizar o processo de deslocamento de sistemas de fluidos, tendo em vista melhorias na integridade da cimentação de poços de petróleo. / [en] One of the most complex and critical stages during the construction ofoil wells is the primary cementing process, defined as the process of installingcement in the annulus between the casing and the exposed formation to thewell [1]. Primary cementing provides permanent zonal isolation to preventcontamination or migration of unwanted fluids in the annulus, protects thecasing from corrosion, and provides hydraulic and mechanical stability forthe casing throughout the productive life of the oil well. In this process,during the drilling stage, irregularities in the cross-section (washouts) can begenerated because of various partial collapses of the open wellbore section dueto the presence of poorly consolidated rocks in the formation. A successfulprimary cementing operation will depend on whether the spacer fluid systemand cement slurry adequately and completely displace the drilling fluid fromthe annulus and washouts.Motivated by this industrial problem, the present dissertation uses aDirect Numerical Simulation (DNS) numerical simulator to systematically analyze the hydrodynamic behavior and calculate the displacement efficiency between two miscible newtonian fluids through an annulus containing an expansion followed by an abrupt contraction. We investigate how different viscositiesand densities of the injected and displaced fluids, their miscibility, injectionrate, and the dimension of the rectangular washout affect the two-phase flow.We consider an axisymmetric geometry during vertical displacement processes,and the governing equations are solved in cylindrical coordinates, allowing theinvestigation of different annular clearances. Due to the miscibility betweenthe fluids, our results predict very high displacement efficiencies, close to 100Non-newtonian fluids are commonly used during the industrial processof primary cementing of oil wells. However, the high displacement efficienciesfound in our results motivate further studies on the influence of miscibilityin displacements of complex fluids. These results also encourage the use ofspacer fluids attempting to control the interfacial properties. Therefore, the useof systems that approximate the rheological and hydrodynamic conditions ofdisplacement between miscible newtonian fluids may contribute to an increasein displacement efficiency and, consequently, optimize the displacement processof fluid systems, aiming at improvements in the integrity of well cementing.

<p>Fibre suspensions in the fluid medium are common in industry, biology, and the environment. Industrial examples of concentrated suspensions include fresh concrete, uncured solid rocket fuel, and biomass slurries; natural examples include silt transfer in rivers and red blood cells in the blood.  These suspensions often include a Newtonian fluid as their suspending medium; still, these suspensions exhibit a plethora of non-Newtonian properties, such as yield stresses, rate-dependent rheology, and normal stresses, to name a few. Other than volume fraction, the type of fiber material, the presence of fluid-fiber or fiber-fiber interactions such as hydrodynamic, Brownian, colloidal, frictional, chemical, and/or electrostatic determine the rheological behavior of suspension. The average inter-fiber gaps between the neighboring fibers decrease significantly as the suspension volume fraction move towards a concentrated regime. As a result, in this regime, inter-fiber interactions become dominant.  Moreover, the surface asperities are present on the fiber surface even in the case of so-called smooth fibers, as fibers in real suspensions are not perfectly smooth. Hence, contact forces arising from the direct touching of the fibers become one of the essential factors in determining the rheology of suspensions.</p> <p>We first describe the causes of yield stress, shear thinning, and normal stress differences in fibre suspensions. We model the fibers as inextensible continuous flexible slender bodies with the Euler-Bernoulli beam equation governing their dynamics suspended in an incompressible Newtonian fluid. The fiber dynamics and fluid flow coupling is achieved using the immersed boundary method (IBM). In addition, the fiber surface roughness lead to inter-fiber contacts resulting in normal and tangential forces between the fibers, which follow Coulomb’s law of<br> friction. The surface roughness is modeled as hemispherical protrusions on the fiber surfaces. In addition to the comparison of the computational model to the experimental results, we demonstrate that attractive interactions lead to yield stress and shear thinning rheology.</p> <p>Furthermore, we investigate the effects of fiber aspect ratio, roughness, flexibility, and volume fraction on the rheology of concentrated suspensions. We find that the suspension viscosity increases with increasing the volume fraction, roughness, fiber rigidity, and aspect ratio. The increase in relative viscosity is the macroscopic manifestation of a similar increase  in the microscopic contact contribution with these parameters. In addition, we observe positive and negative first and second normal stress differences, respectively, in agreement with previous experiments. Lastly, we propose a modified Maron-Pierce law to quantify the the jamming volume fraction with varying fiber aspect ratio and roughness. Additionally, we provide a constitutive model to calculate the viscosity at various volume fractions, aspect ratios, and shear rates.</p>

<p>This is a thesis work proposed by Sweco System in order to carry out a study related to the heating system of a circular fuel oil storage tank or cistern. The study tank is a 23m diameter and 18m height with a storage capacity of around 7500m3 of Eo5 heavy fuel oil. The content ought to be at a minimum storage temperature of 50ºC so that the fuel oil is fluid enough and operation labors can be adequately performed. In fact, these types of heavy fuel oils have fairly high viscosities at lower temperatures and the heating and pumping system can be compromised at temperatures below the pour point. For this purpose a heating system is installed to maintain the fluid warm. So far the system was operated by an oil burner but there are plans to its replacement by a District Heating-heat exchanger combo. Thereby, tank heating needs, flow and thermal patterns and heat transfer within it are principally studied.</p><p> </p><p>Tank boundaries are studied and their thermal resistances are calculated in order to dimension heat supply capacity. The study implies Finite Elements (Comsol Multiphysics) and Finite Volume (Fluent) analysis to work out some stationary heat transfer by conduction cases on some parts and thermal bridges present on these boundaries. Afterwards both cooling and heating processes of the fuel oil are studied using several strategies: basic models and Computational Fluid Dynamics (CFD). CFD work with Fluent is focused on optimizing inlet and outlet topologies. Understanding the cooling process is sought as well; Fluent CFD transient models are simulated in this way as well. Additionally the effect of filling levels is taken into account leading to a multiphase (fuel oil and air) flow cases where especially heating coupling of both phases is analyzed.</p><p> </p><p>Results show that maximum heat supply needs are around 80kW when the tank temperature is around 60ºC and 70kW when it is around 50ºC. Expectedly the main characteristic of the flow turns out to be the buoyancy driven convective pattern. K-ε turbulence viscous models are applied to both heating and cooling processes showing thermal stratification, especially at the bottom of the tank. Hotter fluid above follows very complex flow patterns. During the heating processes models used predict fairly well mixed and homogenous temperature distribution regardless small stratification at the bottom of the tank. In this way no concrete inlet-outlet configuration shows clear advantages over the rest. Due to the insulation of the tank, low thermal conductivity of the fluid and vast amount of mass present in the tank, the cooling process is slow (fluid average temperature drops around 5.7 ºC from 60ºC in 15 days when the tank is full and ambient temperature is considered to be at -20ºC) and lies somewhere in the middle between the solid rigid and perfect mixture cooling processes. However, due to stratification some parts of the fluid reach minimum admissible temperatures much faster than average temperature does. On the other hand, as expected, air phase acts as an additional thermal resistance; anyhow the cooling process is still faster for lower filling levels than the full one.</p> / <p>El presente proyecto fue propuesto por Sweco Systems para llevar a cabo un estudio relacionado con el sistema de calefacción de una cisterna o tanque de almacenamiento de fuel oil circular. Dicho tanque tiene 23 m de diámetro  y 18 m de altura con una capacidad de almacenamiento de alrededor de 7500 m³ de Eo5 fuel oil pesado. El contenido mantenerse a una temperatura mínima de 50 ºC de manera que el fuel oil es suficientemente fluido para que las labores de operación puedan ser ejecutadas adecuadamente. De hecho, estos tipos de fuel oil pesado tienen altas viscosidades a bajas temperaturas y, por tanto, tanto los sistemas de calefacción y como el de bombeo pueden verse comprometidosr a temperaturas por debajo del pour point. Con este fin un sistema de calefacción es instalado para mantener el fluido suficientemente caliente. Hasta el momento, el sistema era operado por un quemador de fuel, sin embargo, hay planes que éste sea sustituido por un combo intercambiador de calor-District Heating. Por lo tanto, principalmente son estudiadas las necesidades de calefacción así como los flujos térmicos y fluidos.</p><p>Se estudian las fronteras del tanque, y sus respectivas resistencias térmicas son calculadas con el fin de dimensionar la capacidad necesaria de suministro de calor. El estudio implica Elementos Finitos (Comsol Multiphysics) y Volúmenes Finitos (Fluent) para elaborar análisis estacionarios de transferencia de calor por conducción en algunos casos. Existen puentes térmicos en las paredes y su importancia es también anallizada. Posteriormente se estudian tanto los procesos de calentamiento y enfriamiento del fuel oil utilizando diversas estrategias: modelos básicos y Dinámica de Fluidos Computacional (CFD). El trabajo con CFD se centra en la optimización de topologías de entradas y salidas del sistema. También es solicitado entender el proceso de enfriamiento; En este sentido, se simulan modelos CFD transitorios de Fluent. Además, el efecto de los niveles de llenado se tiene en cuenta dando lugar a estudios de flujo multifase (fuel oil y aire), haciendo hincapié en el análisis de acoplamiento de transferencia de calor entre las dos fases.</p><p>Los resultados muestran que las necesidades de calefacción máximas son de alrededor de 80kW cuando la temperatura del tanque es de alrededor de 60 º C y 70kW cuando está alrededor de 50 ºC. Como era de esperar, la principal característica de este tipo de flujos es la convección natural resultante de las fuerzas de flotabilidad. Se aplican modelos turbulentos k-ε a los procesos de calentamiento y enfriamiento, mostrando estratificación térmica, sobre todo en la parte inferior de la cisterna. El líquido más caliente que se sitúa encima muestra complejos patrones de flujo. Durante los procesos de calentamiento, los modelos utilizados predicen un buen mezclado y distribución homogénea de la temperatura independientemente de esta pequeña estratificación en la parte inferior de la cisterna. De esta manera, ninguna concreta configuración de entradas-salidas simuladas muestra claras ventajas sobre el resto. Debido al aislamiento de la cisterna, la baja conductividad térmica del fluido y la gran cantidad de masa presente en el tanque el proceso de enfriamiento es lento (la temperatura media del fluido desciende 5.7 º C desde 60 º C en 15 días cuando el tanque está lleno y la temperatura ambiente es de -20 º C) y se encuentra en algún lugar en medio de los procesos de enfriamiento del sólido rígido y perfecta mezcla. Sin embargo, debido a la estratificación, algunas partes el líquido alcanzan la temperatura mínima admisible mucho más rápido que la media de temperatura. Por otra parte, como se esperaba, la fase de aire actúa como una resistencia térmica adicional, de todos modos, el proceso de enfriamiento es aún más rápido para niveles de llenado más bajos que el lleno.</p>

This is a thesis work proposed by Sweco System in order to carry out a study related to the heating system of a circular fuel oil storage tank or cistern. The study tank is a 23m diameter and 18m height with a storage capacity of around 7500m3 of Eo5 heavy fuel oil. The content ought to be at a minimum storage temperature of 50ºC so that the fuel oil is fluid enough and operation labors can be adequately performed. In fact, these types of heavy fuel oils have fairly high viscosities at lower temperatures and the heating and pumping system can be compromised at temperatures below the pour point. For this purpose a heating system is installed to maintain the fluid warm. So far the system was operated by an oil burner but there are plans to its replacement by a District Heating-heat exchanger combo. Thereby, tank heating needs, flow and thermal patterns and heat transfer within it are principally studied.   Tank boundaries are studied and their thermal resistances are calculated in order to dimension heat supply capacity. The study implies Finite Elements (Comsol Multiphysics) and Finite Volume (Fluent) analysis to work out some stationary heat transfer by conduction cases on some parts and thermal bridges present on these boundaries. Afterwards both cooling and heating processes of the fuel oil are studied using several strategies: basic models and Computational Fluid Dynamics (CFD). CFD work with Fluent is focused on optimizing inlet and outlet topologies. Understanding the cooling process is sought as well; Fluent CFD transient models are simulated in this way as well. Additionally the effect of filling levels is taken into account leading to a multiphase (fuel oil and air) flow cases where especially heating coupling of both phases is analyzed.   Results show that maximum heat supply needs are around 80kW when the tank temperature is around 60ºC and 70kW when it is around 50ºC. Expectedly the main characteristic of the flow turns out to be the buoyancy driven convective pattern. K-ε turbulence viscous models are applied to both heating and cooling processes showing thermal stratification, especially at the bottom of the tank. Hotter fluid above follows very complex flow patterns. During the heating processes models used predict fairly well mixed and homogenous temperature distribution regardless small stratification at the bottom of the tank. In this way no concrete inlet-outlet configuration shows clear advantages over the rest. Due to the insulation of the tank, low thermal conductivity of the fluid and vast amount of mass present in the tank, the cooling process is slow (fluid average temperature drops around 5.7 ºC from 60ºC in 15 days when the tank is full and ambient temperature is considered to be at -20ºC) and lies somewhere in the middle between the solid rigid and perfect mixture cooling processes. However, due to stratification some parts of the fluid reach minimum admissible temperatures much faster than average temperature does. On the other hand, as expected, air phase acts as an additional thermal resistance; anyhow the cooling process is still faster for lower filling levels than the full one. / El presente proyecto fue propuesto por Sweco Systems para llevar a cabo un estudio relacionado con el sistema de calefacción de una cisterna o tanque de almacenamiento de fuel oil circular. Dicho tanque tiene 23 m de diámetro  y 18 m de altura con una capacidad de almacenamiento de alrededor de 7500 m3 de Eo5 fuel oil pesado. El contenido mantenerse a una temperatura mínima de 50 ºC de manera que el fuel oil es suficientemente fluido para que las labores de operación puedan ser ejecutadas adecuadamente. De hecho, estos tipos de fuel oil pesado tienen altas viscosidades a bajas temperaturas y, por tanto, tanto los sistemas de calefacción y como el de bombeo pueden verse comprometidosr a temperaturas por debajo del pour point. Con este fin un sistema de calefacción es instalado para mantener el fluido suficientemente caliente. Hasta el momento, el sistema era operado por un quemador de fuel, sin embargo, hay planes que éste sea sustituido por un combo intercambiador de calor-District Heating. Por lo tanto, principalmente son estudiadas las necesidades de calefacción así como los flujos térmicos y fluidos. Se estudian las fronteras del tanque, y sus respectivas resistencias térmicas son calculadas con el fin de dimensionar la capacidad necesaria de suministro de calor. El estudio implica Elementos Finitos (Comsol Multiphysics) y Volúmenes Finitos (Fluent) para elaborar análisis estacionarios de transferencia de calor por conducción en algunos casos. Existen puentes térmicos en las paredes y su importancia es también anallizada. Posteriormente se estudian tanto los procesos de calentamiento y enfriamiento del fuel oil utilizando diversas estrategias: modelos básicos y Dinámica de Fluidos Computacional (CFD). El trabajo con CFD se centra en la optimización de topologías de entradas y salidas del sistema. También es solicitado entender el proceso de enfriamiento; En este sentido, se simulan modelos CFD transitorios de Fluent. Además, el efecto de los niveles de llenado se tiene en cuenta dando lugar a estudios de flujo multifase (fuel oil y aire), haciendo hincapié en el análisis de acoplamiento de transferencia de calor entre las dos fases. Los resultados muestran que las necesidades de calefacción máximas son de alrededor de 80kW cuando la temperatura del tanque es de alrededor de 60 º C y 70kW cuando está alrededor de 50 ºC. Como era de esperar, la principal característica de este tipo de flujos es la convección natural resultante de las fuerzas de flotabilidad. Se aplican modelos turbulentos k-ε a los procesos de calentamiento y enfriamiento, mostrando estratificación térmica, sobre todo en la parte inferior de la cisterna. El líquido más caliente que se sitúa encima muestra complejos patrones de flujo. Durante los procesos de calentamiento, los modelos utilizados predicen un buen mezclado y distribución homogénea de la temperatura independientemente de esta pequeña estratificación en la parte inferior de la cisterna. De esta manera, ninguna concreta configuración de entradas-salidas simuladas muestra claras ventajas sobre el resto. Debido al aislamiento de la cisterna, la baja conductividad térmica del fluido y la gran cantidad de masa presente en el tanque el proceso de enfriamiento es lento (la temperatura media del fluido desciende 5.7 º C desde 60 º C en 15 días cuando el tanque está lleno y la temperatura ambiente es de -20 º C) y se encuentra en algún lugar en medio de los procesos de enfriamiento del sólido rígido y perfecta mezcla. Sin embargo, debido a la estratificación, algunas partes el líquido alcanzan la temperatura mínima admisible mucho más rápido que la media de temperatura. Por otra parte, como se esperaba, la fase de aire actúa como una resistencia térmica adicional, de todos modos, el proceso de enfriamiento es aún más rápido para niveles de llenado más bajos que el lleno.