Dissertations / Theses on the topic 'Laminar flow. Fluid dynamics. Two-phase flow'

Master of Science<br>Department of Mechanical and Nuclear Engineering<br>Steven Eckels<br>Both cavitating and flashing flows are important phenomena in fluid flow. Cavitating flow, a common consideration in valves, orifices, and metering devices, is also a concern in loss of coolant accidents for liquid water in power plants when saturation pressures are below atmospheric pressure. Flashing flow is a common consideration for devices such as relief and expansion valves and fluid injectors as well as for loss of coolant accidents in which the coolant’s saturation pressure is above atmospheric. Of the two phenomena, flashing flow has received greater interest due to its applicability to safety concerns, though cavitating flow is perhaps of greater interest in terms of energy efficiency. It is possible for cavitating and flashing flow to actually become sonic. That is, the local velocity of a fluid can exceed the local speed of sound due to the unique properties of two-phase mixtures. When a flow becomes sonic, it is possible for the flow to accelerate and impose additional energy losses that would not otherwise occur. Models of this aspect of two-phase flow are not well developed, typically only being presented for the case of constant area ducts. In this paper two models for cavitating sonic flow are developed and described by applying the integral forms of the mass, momentum, and energy equations to a control volume of variable cross-sectional area. These models, based on the homogeneous equilibrium model (HEM) and separated flow model, are then applied to experimental data taken by the author with R-134a as the fluid of interest. Experimental data were taken with four instrumented converging-diverging nozzles of various geometries using a custom testing rig that allowed for precise control and measurement of flow parameters such as mass flow, temperature, and pressure. The resultant data from the models are then examined, focusing on the resultant velocities, Mach numbers, quality, and shear stresses.

Dissertation (Ph.D.) -- Worcester Polytechnic Institute.<br>Keywords: Multiphase flow; Two-fluid modeling; Direct numerical simulation; Two fluid modeling. Includes bibliographical references (leaves 116-119).

Thesis (M.S.)--University of Missouri-Columbia, 2008.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 19, 2009) Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2006.<br>Title from document title page. Document formatted into pages; contains viii, 88 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 73-76).

Physics of immiscible two-phase flow in porous media is relevant for various industrial and environmental applications. Wettability defined as the relative affinity of fluids with the solid surface has a significant impact on the dynamics of immiscible displacement. Although wettability effects on the macroscopic fluid flow behaviour are well known, there is a lack of pore-scale understanding. Considering the crucial role of wettability in a diverse range of applications; this research aims to provide a pore-scale picture of interface configuration induced by variations in the wetting characteristics of porous media. Besides, this study also relates the pore-scale interfacial phenomena with the macroscopic response of fluids. High-resolution direct numerical simulations (DNS) at multiscale (single capillary and a highly heterogeneous porous media) were performed using computational fluid dynamics (CFD) approach in which the Navier-Stokes equation coupled with the volume of fluid method is solved to represent immiscible displacement. Numerical results demonstrate that at pore scale as the wettability of porous media changes from strong to intermediate wet the effects of pore geometry (that includes corner angle and orientation angle) on the interfacial dynamics also enhances. This was demonstrated by the non-monotonic behaviour of entry capillary pressure at the junction of pore, curvature reversal in the converging-diverging capillary and the co-existence of concave and convex interfaces in heterogeneous porous media with uniform contact angle distribution. In addition to simulations, theoretical argument is also presented that rationalize the underlying physics of complex, yet intriguing interfacial phenomena shown by DNS. Overall this research extends the fundamental understanding of multiphase flow in porous media and paves the way for future studies on porous media.

Master of Science<br>Department of Mechanical and Nuclear Engineering<br>Steven Eckels and Mohammad Hosni<br>This research presents results from experimental and numerical investigations of two-phase flow pattern analysis in a staggered tube bundle. Shell-side boiling tube bundles are used in a variety of industries from nuclear power plants to industrial evaporators. Fluid flow patterns in tube bundles affect pressure drop, boiling characteristics, and tube vibration. R-134a was the working fluid in both the experimental and computational fluid dynamics (CFD) analysis for this research. Smooth and enhanced staggered tube bundles were studied experimentally using a 1.167 pitch to diameter ratio. The experimental tube bundles and CFD geometry consist of 20 tubes with five tubes per pass. High speed video was recorded during the experimental bundle boiling. Bundle conditions ranged in mass fluxes from 10-35 kg/m[superscript]2.s and inlet qualities from 0-70% with a fixed heat flux. Classification of the flow patterns from these videos was performed using flow pattern definitions from literature. Examples of smooth and enhanced bundle boiling high speed videos are given through still images. The flow patterns are plotted and compared with an existing flow pattern map. Good agreement was found for the enhanced tube bundle while large discrepancies exist for the smooth tube bundle. The CFD simulations were performed without heat transfer with non-symmetrical boundary conditions at the side walls, simulating rectangular bundles used in this and other research. The two-phase volume of fluid method was used to construct vapor interfaces and measure vapor volume fraction. A probability density function technique was applied to the results to determine flow patterns from the simulations using statistical parameters. Flow patterns were plotted on an adiabatic flow pattern map from literature and excellent agreement is found between the two. The agreement between simulation results and experimental data from literature emphasizes the use of numerical techniques for tube bundle design.

Moving contact line problems appear in many natural and industrial processes. A contact line is formed where the interface between two immiscible fluids meets a solid wall. Examples from everyday life include raindrops falling on a window and water bugs resting on water surfaces. In many cases the dynamics of the contact line affects the overall behavior of the system. Industrial applications where the contact line behavior is important include gas and oil recovery in porous media, lubrication, inkjet printing and microfluidics. Computer simulations are fundamental tools to understand and predict the behavior.   In this thesis we look at numerical simulations of dynamic contact line problems. Despite their importance, the physics of moving contact lines is poorly understood. The standard Navier-Stokes equations together with the conventional no-slip boundary condition predicts a singularity in the shear stresses at the contact line. Atomistic processes at the contact line come into play, and it is necessary to include these processes in the model to resolve the singularity. In the case of capillary driven flows for example, it has been observed that the microscopic contact line dynamics has a large impact on the overall macroscopic flow. In Paper I we present a new multiscale model for numerical simulation of flow of two immiscible and incompressible fluids in the presence of moving contact points (i.e. two-dimensional problems). The paper presents a new boundary methodology based on combining a relation between the apparent contact angle and the contact point velocity, and a similarity solution for Stokes flow at a planar interface (the analytic Huh and Scriven velocity). The relation between the angle and the velocity is determined by performing separate microscopic simulations. The classical Huh and Scriven solution is only valid for flow over flat walls. In Paper II we use perturbation analysis to extend the solution to flow over curved walls. Paper III presents the parallel finite element solver that is used to perform the numerical experiments presented in this thesis. Finally, the new multiscale model (presented in Paper I) is applied to a relevant microfluidic research problem in Paper IV. For this problem it is very important to have a model that accurately takes the atomistic effects at contact lines into account.

Submerged flat sheet membranes are mostly used in membrane bioreactors for wastewater treatment. The major problems for these modules are concentration polarization and subsequent fouling. By using gas-liquid two-phase flow, these problems can be ameliorated. This thesis aimed to optimize the use of gas-liquid two-phase flow as a cleaning mechanism for submerged flat sheet membrane. The effect of various hydrodynamic factors such as airflow rate, nozzle size, nozzle geometry, intermittent bubbling, intermittent filtration, channel gap width, feed concentration and membrane baffles were investigated for model feed materials (yeast suspensions and mixed liquor from activated sludge plants). Insights into mechanisms by which two-phase flow reduces fouling for submerged flat sheet membranes were obtained by using Computational Fluid Dynamics. Experiments conducted showed that an optimal airflow rate exists beyond which no further flux enhancement was achieved. Fouling reduction increased with nozzle size at constant airflow. Nozzles of equal surface area but different geometries performed differently in terms of fouling reduction. Bubble size distribution analyses revealed that the percentage of larger bubbles and bubble rise velocities increased with the airflow rate and nozzle size. Thus the results of this study suggest that the effectiveness of two-phase flow depends on the bubble size. CFD simulations revealed that average shear stress on the membrane increased with airflow rate and bubble size and further indicated that an optimal bubble size possible exists. Using intermittent filtration as an operating strategy was found to be more beneficial than continuous filtration. This study also showed the importance of the size of the gap between the submerged flat sheet membranes. Increasing the gap from 7 mm to 14 mm resulted in an increase in fouling by about 40% based on the rate of increase in suction pressure (dTMP/dt). Finally, this is the first study which investigated the effect of baffles in improving air distribution across a submerged flat sheet membrane. It was found that baffles decreased the rate of fouling at least by a factor of 3.0 based on the dTMP/dt data.

Flow mechanisms affect transport processes during condensation. Most studies on two-phase flow regimes are qualitative in nature, typically providing only information to guide the identification of the respective regimes and the transitions between them. These studies have, however, not yielded quantitative information to assist the development of pressure drop and heat transfer models. Such qualitative studies have also yielded results with considerable variability between investigators. A comprehensive investigation of flow mechanisms, void fraction, pressure drop and heat transfer during condensation of R404A in microchannels was conducted. In contrast to all prior investigations, high-speed video recordings and image analyses were used to directly measure void fraction, slug frequencies, vapor bubble velocity, vapor bubble dimensions and liquid film thicknesses in tube diameters ranging from 0.508 to 3.00 mm. Experiments were conducted at reduced pressures and mass fluxes ranging from 0.38 to 0.77 and 200 to 800 kg m-2 s-1, respectively, to document their influences on the condensation process at local vapor qualities ranging from 0 to 1. This information was used to develop a model for the void fraction in condensing flows. A complementing set of heat transfer and pressure drop measurements were conducted on the same geometries at similar conditions, and the void fraction model was used in conjunction with these measurements to develop improved heat transfer and pressure drop models. This comprehensive set of experiments and analyses yields a self-consistent and accurate treatment of high-pressure condensation in small hydraulic diameter geometries. Furthermore, the heat transfer model was found to agree well with condensing ammonia and carbon dioxide data that were obtained at significantly different conditions in different tube diameters. The added physical understanding of the condensation process and the models developed will serve as important building blocks for the design of microscale condensers and thermal systems.

Un estudio numérico del comportamiento térmico y fluido-dinámico de flujos bifásicos, liquido-gas, en conductos es presentado. El análisis numérico es basado en dos diferentes modelos. El primer modelo es conocido como quasi-homogéneo, este modelo asume el flujo bifásico como una mezcla homogénea, que esta caracterizada por un flujo másico, una presión y una temperatura de mezcla. Estas tres variables son encontradas por medio de la resolución numérica de las ecuaciones de conservación de masa, momento y energía. Las velocidades de las fases gas y liquida pueden ser evaluadas a partir del flujo másico total de mezcla y de la distribución de una de las fases en el volumen, la cual es determinada mediante expresiones empíricas. Aunque el modelo quasi-homogéneo es capaz de dar buenos resultados en diferentes aplicaciones donde el flujo bifásico esta presente, este modelo no puede dar información de cada una de las fases independientemente. Sí el modelo quasi-homogéneo es aplicado considerando las restricciones con algunos configuraciones de flujo y el hecho de no incluir los términos de intercambio a través de la interfase, este modelo es capaz de convertirse en una buena herramienta de estimación del comportamiento térmico y fluido-dinámico en diferentes sistemas térmicos, donde el flujo bifásico esta presente. El segundo modelo es conocido como dos-fluidos, este modelo permite considerar que el liquido y el gas coexisten en un mismo volumen de control y que cada una de las fases esta caracterizada por tener una velocidad y una temperatura diferente. Este modelo tiene en cuenta las interacciones entre cada una de las fases y la interfase, así es capaz de reconocer la influencia de los intercambios de masa, momento y energía a través de la interfase. El modelo de dos-fluidos necesita más información empírica que el modelo quasi-homogéneo para cerrar y resolver el sistema de ecuaciones que lo caracteriza. <br/><br/>La simulación numérica ha sido desarrollada por medio de la técnica de los volúmenes finitos basada en una integración transitoria, unidimensional o bidimensional de las ecuaciones de continuidad de masa, momento lineal y energía. La presión, las velocidades, las temperaturas y la distribución de cada una da las fases al interior del conducto son obtenidas por medio de la resolución de las ecuaciones gobernantes.<br/><br/>Un método semi-implícito basado en el conocido método de corrección de presiones para resolver fluidos en una fase SIMPLE, ha sido empleado para resolver el acoplamiento entre la presión y la velocidad. Los algoritmos de resolución para cada uno de los modelos desarrollados en esta Tesis son detallados.<br/><br/>La verificación y validación de los modelos presentados en este trabajo se han realizado contra expresiones analíticas y datos experimentales obtenidos desde la literatura técnica o mediante la infraestructura experimental del CTTC. Una comparativa de resultados entre el modelo quasi-homogéneo y el modelo de dos-fluidos para un caso unidimensional es presentado. Además, dos casos reportados en la literatura han sido usados para comparar los resultados del modelo de dos-fluidos en dos dimensiones.<br/><br/><br/>Aplicaciones de los modelos desarrollados en esta Tesis son presentados con el propósito de mostrar las posibilidades ofrecidas por ellos para mejorar el diseño de diferentes equipos térmicos y evitar condiciones de trabajo no deseadas. Un intercambiador de calor del tipo de doble tubo es analizado, observando la influencia de diferentes parámetros sobre el comportamiento térmico y fluido-dinámico. La resolución numérica de un intercambiador del tipo aleta y tubo trabajando como un evaporador o un condensador ha sido comparado con datos experimentales, llegando a obtener un buen ajuste entre ellos. Finalmente, las condiciones de trabajo de un panel solar son optimizadas mediante la simulación numérica, con el objetivo de evitar alcanzar condiciones peligrosas que produzcan daños severos a la instalación.

In order to explain the observed time-dependent salinity variations in seafloor hydrothermal vent fluids, quasi-numerical and fully numerical fluid flow models of the NaCl-H2O system are constructed. For the quasi-numerical model, a simplified treatment of phase separation of seawater near an igneous dike is employed to obtain rough estimates of the thickness and duration of the two-phase zone, the amount of brine formed, and its distribution in the subsurface. For the fully numerical model, the equations governing fluid flow, the thermodynamic relations between various quantities employed, and the coupling of these elements together in a time marching scheme is discussed. The fully numerical model is benchmarked against previously published heat pipe and Elder problem simulation results, and is shown to be largely in agreement with those results. A number of simulation results are presented in the context of two-phase flow and phase separation within the framework of the single pass model. It is found that a quasi-stable two-phase (liquid + vapor) zone at depth below the hydrothermal discharge outlet gives rise to vent fluid with lower than normal seawater salinity. Additionally, it is shown that increasing the spatial extent of the two-phase zone can lower vent fluid salinity. The numerical approach used in this thesis is able to generate salinity patterns predicted by a widely held conceptual model of vent fluid salinity variation, and may be able to explain the vent fluid salinities and temperatures found at the Main Endeavour Vent Field on the Juan de Fuca Ridge, as this approach is able to produce simulated vent fluid salinities that match observed values from the Endeavour Field vents Dante and Hulk.

The study and modelling of two-phase flow, even the simplest ones such as the bubbly flow, remains a challenge that requires exploring the physical phenomena from different spatial and temporal resolution levels. CFD (Computational Fluid Dynamics) is a widespread and promising tool for modelling, but nowadays, there is no single approach or method to predict the dynamics of these systems at the different resolution levels providing enough precision of the results. The inherent difficulties of the events occurring in this flow, mainly those related with the interface between phases, makes that low or intermediate resolution level approaches as system codes (RELAP, TRACE, ...) or 3D TFM (Two-Fluid Model) have significant issues to reproduce acceptable results, unless well-known scenarios and global values are considered. Instead, methods based on high resolution level such as Interfacial Tracking Method (ITM) or Volume Of Fluid (VOF) require a high computational effort that makes unfeasible its use in complex systems. In this thesis, an open-source simulation framework has been designed and developed using the OpenFOAM library to analyze the cases from microescale to macroscale levels. The different approaches and the information that is required in each one of them have been studied for bubbly flow. In the first part, the dynamics of single bubbles at a high resolution level have been examined through VOF. This technique has allowed to obtain accurate results related to the bubble formation, terminal velocity, path, wake and instabilities produced by the wake. However, this approach has been impractical for real scenarios with more than dozens of bubbles. Alternatively, this thesis proposes a CFD Discrete Element Method (CFD-DEM) technique, where each bubble is represented discretely. A novel solver for bubbly flow has been developed in this thesis. This includes a large number of improvements necessary to reproduce the bubble-bubble and bubble-wall interactions, turbulence, velocity seen by the bubbles, momentum and mass exchange term over the cells or bubble expansion, among others. But also new implementations as an algorithm to seed the bubbles in the system have been incorporated. As a result, this new solver gives more accurate results as the provided up to date. Following the decrease on resolution level, and therefore the required computational resources, a 3D TFM have been developed with a population balance equation solved with an implementation of the Quadrature Method Of Moments (QMOM). The solver is implemented with the same closure models as the CFD-DEM to analyze the effects involved with the lost of information due to the averaging of the instantaneous Navier-Stokes equation. The analysis of the results with CFD-DEM reveals the discrepancies found by considering averaged values and homogeneous flow in the models of the classical TFM formulation. Finally, for the lowest resolution level approach, the system code RELAP5/MOD3 is used for modelling the bubbly flow regime. The code has been modified to reproduce properly the two-phase flow characteristics in vertical pipes, comparing the performance of the calculation of the drag term based on drift-velocity and drag coefficient approaches.<br>El estudio y modelado de flujos bifásicos, incluso los más simples como el bubbly flow, sigue siendo un reto que conlleva aproximarse a los fenómenos físicos que lo rigen desde diferentes niveles de resolución espacial y temporal. El uso de códigos CFD (Computational Fluid Dynamics) como herramienta de modelado está muy extendida y resulta prometedora, pero hoy por hoy, no existe una única aproximación o técnica de resolución que permita predecir la dinámica de estos sistemas en los diferentes niveles de resolución, y que ofrezca suficiente precisión en sus resultados. La dificultad intrínseca de los fenómenos que allí ocurren, sobre todo los ligados a la interfase entre ambas fases, hace que los códigos de bajo o medio nivel de resolución, como pueden ser los códigos de sistema (RELAP, TRACE, etc.) o los basados en aproximaciones 3D TFM (Two-Fluid Model) tengan serios problemas para ofrecer resultados aceptables, a no ser que se trate de escenarios muy conocidos y se busquen resultados globales. En cambio, códigos basados en alto nivel de resolución, como los que utilizan VOF (Volume Of Fluid), requirieren de un esfuerzo computacional tan elevado que no pueden ser aplicados a sistemas complejos. En esta tesis, mediante el uso de la librería OpenFOAM se ha creado un marco de simulación de código abierto para analizar los escenarios desde niveles de resolución de microescala a macroescala, analizando las diferentes aproximaciones, así como la información que es necesaria aportar en cada una de ellas, para el estudio del régimen de bubbly flow. En la primera parte se estudia la dinámica de burbujas individuales a un alto nivel de resolución mediante el uso del método VOF (Volume Of Fluid). Esta técnica ha permitido obtener resultados precisos como la formación de la burbuja, velocidad terminal, camino recorrido, estela producida por la burbuja e inestabilidades que produce en su camino. Pero esta aproximación resulta inviable para entornos reales con la participación de más de unas pocas decenas de burbujas. Como alternativa, se propone el uso de técnicas CFD-DEM (Discrete Element Methods) en la que se representa a las burbujas como partículas discretas. En esta tesis se ha desarrollado un nuevo solver para bubbly flow en el que se han añadido un gran número de nuevos modelos, como los necesarios para contemplar los choques entre burbujas o con las paredes, la turbulencia, la velocidad vista por las burbujas, la distribución del intercambio de momento y masas con el fluido en las diferentes celdas por cada una de las burbujas o la expansión de la fase gaseosa entre otros. Pero también se han tenido que incluir nuevos algoritmos como el necesario para inyectar de forma adecuada la fase gaseosa en el sistema. Este nuevo solver ofrece resultados con un nivel de resolución superior a los desarrollados hasta la fecha. Siguiendo con la reducción del nivel de resolución, y por tanto los recursos computacionales necesarios, se efectúa el desarrollo de un solver tridimensional de TFM en el que se ha implementado el método QMOM (Quadrature Method Of Moments) para resolver la ecuación de balance poblacional. El solver se desarrolla con los mismos modelos de cierre que el CFD-DEM para analizar los efectos relacionados con la pérdida de información debido al promediado de las ecuaciones instantáneas de Navier-Stokes. El análisis de resultados de CFD-DEM permite determinar las discrepancias encontradas por considerar los valores promediados y el flujo homogéneo de los modelos clásicos de TFM. Por último, como aproximación de nivel de resolución más bajo, se investiga el uso uso de códigos de sistema, utilizando el código RELAP5/MOD3 para analizar el modelado del flujo en condiciones de bubbly flow. El código es modificado para reproducir correctamente el flujo bifásico en tuberías verticales, comparando el comportamiento de aproximaciones para el cálculo del término d<br>L'estudi i modelatge de fluxos bifàsics, fins i tot els més simples com bubbly flow, segueix sent un repte que comporta aproximar-se als fenòmens físics que ho regeixen des de diferents nivells de resolució espacial i temporal. L'ús de codis CFD (Computational Fluid Dynamics) com a eina de modelatge està molt estesa i resulta prometedora, però ara per ara, no existeix una única aproximació o tècnica de resolució que permeta predir la dinàmica d'aquests sistemes en els diferents nivells de resolució, i que oferisca suficient precisió en els seus resultats. Les dificultat intrínseques dels fenòmens que allí ocorren, sobre tots els lligats a la interfase entre les dues fases, fa que els codis de baix o mig nivell de resolució, com poden ser els codis de sistema (RELAP,TRACE, etc.) o els basats en aproximacions 3D TFM (Two-Fluid Model) tinguen seriosos problemes per a oferir resultats acceptables , llevat que es tracte d'escenaris molt coneguts i se persegueixen resultats globals. En canvi, codis basats en alt nivell de resolució, com els que utilitzen VOF (Volume Of Fluid), requereixen d'un esforç computacional tan elevat que no poden ser aplicats a sistemes complexos. En aquesta tesi, mitjançant l'ús de la llibreria OpenFOAM s'ha creat un marc de simulació de codi obert per a analitzar els escenaris des de nivells de resolució de microescala a macroescala, analitzant les diferents aproximacions, així com la informació que és necessària aportar en cadascuna d'elles, per a l'estudi del règim de bubbly flow. En la primera part s'estudia la dinàmica de bambolles individuals a un alt nivell de resolució mitjançant l'ús del mètode VOF. Aquesta tècnica ha permès obtenir resultats precisos com la formació de la bambolla, velocitat terminal, camí recorregut, estela produida per la bambolla i inestabilitats que produeix en el seu camí. Però aquesta aproximació resulta inviable per a entorns reals amb la participació de més d'unes poques desenes de bambolles. Com a alternativa en aqueix cas es proposa l'ús de tècniques CFD-DEM (Discrete Element Methods) en la qual es representa a les bambolles com a partícules discretes. En aquesta tesi s'ha desenvolupat un nou solver per a bubbly flow en el qual s'han afegit un gran nombre de nous models, com els necessaris per a contemplar els xocs entre bambolles o amb les parets, la turbulència, la velocitat vista per les bambolles, la distribució de l'intercanvi de moment i masses amb el fluid en les diferents cel·les per cadascuna de les bambolles o els models d'expansió de la fase gasosa entre uns altres. Però també s'ha hagut d'incloure nous algoritmes com el necessari per a injectar de forma adequada la fase gasosa en el sistema. Aquest nou solver ofereix resultats amb un nivell de resolució superior als desenvolupat fins la data. Seguint amb la reducció del nivell de resolució, i per tant els recursos computacionals necessaris, s'efectua el desenvolupament d'un solver tridimensional de TFM en el qual s'ha implementat el mètode QMOM (Quadrature Method Of Moments) per a resoldre l'equació de balanç poblacional. El solver es desenvolupa amb els mateixos models de tancament que el CFD-DEM per a analitzar els efectes relacionats amb la pèrdua d'informació a causa del promitjat de les equacions instantànies de Navier-Stokes. L'anàlisi de resultats de CFD-DEM permet determinar les discrepàncies ocasionades per considerar els valors promitjats i el flux homogeni dels models clàssics de TFM. Finalment, com a aproximació de nivell de resolució més baix, s'analitza l'ús de codis de sistema, utilitzant el codi RELAP5/MOD3 per a analitzar el modelatge del fluxos en règim de bubbly flow. El codi és modificat per a reproduir correctament les característiques del flux bifàsic en canonades verticals, comparant el comportament d'aproximacions per al càlcul del terme de drag basades en velocitat de drift flux model i de les basades en coe<br>Peña Monferrer, C. (2017). Computational fluid dynamics multiscale modelling of bubbly flow. A critical study and new developments on volume of fluid, discrete element and two-fluid methods [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90493<br>TESIS

External loop airlift reactors are widely used for biochemical applications such as syngas fermentation and wastewater treatment. To further understand the inherent gas-liquid flow physics within the reactors, computational modeling and simulations of hydrodynamics for air-water external loop airlift reactors were investigated. The gas-liquid flow dynamics in a bubble column were simulated using a FORTRAN code developed by Los Alamos National Laboratory, CFDLib, which employs an Eulerian-Eulerian ensemble averaged method. A two-dimensional Cartesian coordinate system was used to conduct an extensive grid resolution study; it was found that grid cells smaller than the bubble diameter produced unstable solutions. Next, closure models for drag force and turbulent viscosity were investigated for a simple bubble column geometry. The effects of using a bubble pressure model and two drag coefficient models, the White model and the Schiller-Naumann model, were investigated. The bubble pressure model performed best for homogeneous (low velocity) flows and the Schiller-Naumann model was best for all flow regimes. Based on the studies for bubble column flows, an external loop airlift reactor was simulated using both two- and three-dimensional coordinates and results for gas holdup and riser velocity agreed better with experimental data for the 3D simulations. It was concluded that when performing 2D and 3D simulations, care must be taken when specifying the effective bubble diameter size, especially at high flow rates. Population balance models (PBM) for bubble break-up and coalescence were implemented into CFDLib, validated with experiments, and simulated for the external loop airlift reactor at high inlet superficial gas velocities. The PBM predictions for multiple bubble sizes were comparable with the single bubble size simulations; however, the PBM simulations better predicted the formation of the gas bubble in the downcomer. The 3D PBM simulations also gave better predictions for the average bubble diameter size in the riser. It was concluded that a two-dimensional domain is adequate for gas-liquid flow simulations of a simple bubble column geometry, whereas three-dimensional simulations are required for the complex airlift reactor geometry. To conclude, a two-fluid Eulerian-Eulerian model coupled with a PBM is needed for quantitative as well as physical predictions of gas-liquid external loop airlift reactor flows at high inlet superficial gas velocities.<br>Ph. D.

Bien que performantes pour la capture des chocs, la plupart des méthodes de simulation standards ne sont pas adaptées à des régimes de Mach variés. Des méthodes numériques innovantes, utilisant des schémas de type Volumes Finis, robustes et précises uniformément selon le nombre de Mach (dites "tout régime") ont été récemment élaborées au CEA. Ces méthodes permettent de résoudre les équations de la mécanique des fluides compressibles pour capturer des chocs, mais aussi pour simuler des écoulements à très faible vitesse. Fort de ces résultats prometteurs, nous proposons dans cette thèse de mettre à l’épreuve ces nouvelles méthodes dans deux domaines applicatifs différents: les écoulements diphasiques à petit échelle et les écoulements compressibles en astrophysique. Pour ces deux domaines la simulation multi-régime est un point difficile. En effet, ces deux contextes d’applications ont pour cœur une modélisation d’écoulement compressible mais mettent en jeu des phénomènes de convection et de compressibilité à des régimes de Mach très variés. L’approche "tout régime" permettra de capturer des phénomènes très compressibles tout en gardant la précision sur les écoulements basse vitesse<br>Although classic simulation methods for compressible flow are efficient for shock capturing, they are not adapted to variable Mach regimes. Innovative methods using Finite Volume numerical schemes, robust and uniformly accurate with respect to the Mach number (so-called "all-regime"), were recently developed at CEA. These methods allow to solve the equations of compressible flows for both shocks capturing and flows involving very low material speed. Using the ground of these promising results, we propose within this thesis to challenge these new methods in two different application areas: small scale two-phase flows and compressible flows in astrophysics. For both contexts the multi-regime simulation is a key issue: they both rely on a compressible flow modeling but involve convection and compressibility in highly-variable Mach regimes. The "all-regime" approach is a good candidate for capturing highly compressible phenomena while preserving the accuracy in the low speed flows

The diffusion absorption refrigeration (DAR) cycle is a promising technology for fully thermally driven cooling. It is well suited to applications in medicine refrigeration and air-conditioning in off-grid settings. However, design and engineering knowhow for the technology is limited; therefore, system development has historically been an iterative and expensive process. Additionally, conventional system designs require high-grade energy input for operation, and are unsuitable for low-temperature solar- or waste-heat activated applications. In the present effort, component- and system-level DAR engineering analyses are performed. Detailed bubble-pump generator (BPG) component models are developed, and are validated experimentally and with direct simulations. Investigations into the BPG focus on the Taylor flow pattern in the intermediate Bond number regime, which has not yet been thoroughly characterized in the literature, and has numerous industry applications, including nuclear fuel processing and well dewatering. A coupling-fluid heated BPG design is also investigated experimentally for low-source-temperature operation. Phase-change simulation methodologies are developed to rigorously study the continuously developing flow pattern in this BPG configuration. Detailed component-level models are also formulated for all of the other DAR heat and mass exchangers, and are integrated to yield a complete system-level model. Results from these modeling studies are applied to develop a novel fully passive low-source-temperature (110 - 130°C) DAR system that delivers refrigeration grade cooling. This design achieves operation at target conditions through the use of alternate working fluids (NH3-NaSCN-He), the coupling-fluid heated BPG, and a novel absorber configuration. The complete DAR system is demonstrated experimentally, and evaluated over a range of operating conditions. Experimental results are applied to assess and refine component- and system- level models.

This thesis focuses on the hydrodynamics of gas-liquid Taylor flow (or slug flow) in microchannels. These flows, which are generally dominated by surface tension forces, have been investigated in rectangular channels of various cross-sectional aspect ratios by means of both experimental visualizations and numerical simulations. The first experimental part aims at characterizing the bubble generation process (bubble length and frequency of break-up) depending on the operating conditions, the fluid properties, as well as the junction where both fluids merge. Numerical simulations of fully developed Taylor flow have been carried out with the JADIM code. The computation of such surface tension dominated flows requires an accurate calculation of the surface tension force. Some limitations of the Volume of Fluid method have been highlighted and a Level Set method has been developed in order to improve the calculation of capillary effects. Both methods have been compared in detail in terms of spurious currents. 3D numerical simulations have been performed and the influence of the capillary number, as well as the effects of geometry have been highlighted. Inertial effects have been taken into account and their influence on the pressure drop has been shown to be non-negligible. Mixing in the liquid slug has also been studied.

This thesis describes validated improvements in the modelling of micron-sized particle deposition within gas turbine engine secondary air systems. The initial aim of the research was to employ appropriate models of instantaneous turbulent flow behaviour to RANS CFD simulations, allowing the trajectory of solid particulates in the flow to be accurately predicted. Following critical assessment of turbophoretic models, the continuous random walk (CRW) model was chosen to predict instantaneous fluid fluctuating velocities. Particle flow, characterised by non-dimensional deposition velocity and particle relaxation time, was observed to match published experimental vertical pipe flow data. This was possible due to redefining the integration time step in terms of Kolmagorov and Lagrangian time scales, reducing the disparity between simulations and experimental data by an order of magnitude. As no high temperature validation data for the CRW model were available, an experimental rig was developed to conduct horizontal pipe flow experiments under engine realistic conditions. Both the experimental rig, and a new particulate concentration measurement technique, based on post test aqueous solution electrical conductivity, were qualified at ambient conditions. These new experimental data compare well to published data at non-dimensional particle relaxation times below 7. Above, a tail off in the deposition rate is observed, potentially caused by a bounce or shear removal mechanism at higher particle kinetic energy. At elevated temperatures and isothermal conditions, similar behaviour is observed to the ambient data. Under engine representative thermophoretic conditions, a negative gas to wall temperature gradient is seen to increase deposition by up to 4.8 times, the reverse decreasing deposition by a factor of up to 560 relative to the isothermal data. Numerical simulations using the CRW model under-predict isothermal deposition, though capturing relative thermophoretic effects well. By applying an anisotropic Lagrangian time scale, and cross trajectory effects of the external gravitational force, good agreement was observed, the first inclusion of the effect within the CRW model. A dynamic mesh morphing method was then developed, enabling the effect of large scale particle deposition to be included in simulations, without continual remeshing of the fluid domain. Simulation of an impingement jet array showed deposition of characteristic mounds up to 30% of the hole diameter in height. Simulation of a passage with film-cooling hole off-takes generated hole blockage of up to 40%. These cases confirmed that the use of the CRW generated deposition locations in line with scant available experimental data, but widespread airline fleet experience. Changing rates of deposition were observed with the evolution of the deposits in both cases, highlighting the importance of capturing changing passage geometry through dynamic mesh morphing. The level of deposition observed, was however, greater than expected in a real engine environment and identifies a need to further refine bounce-stick and erosion modelling to complement the improved prediction of impact location identified in this thesis.

Biomass is considered a biorenewable alternative energy resource that can potentially reduce the use of natural gas and provide low cost power production or process heating needs. Biomass hydrodynamics in a fluidized bed are extremely important to industries that are using biomass material in gasfication processes to yield high quality producer gas. However, biomass particles are typically difficult to fluidize due to their peculiar shape and a second inert material, such as sand, is typically added to the bed. The large differences in size and density between the biomass and inert particles lead to nonuniform distribution of the biomass within the fluidized bed, and particle interactions and mixing become major issues. The main goal of this research was to use CFD as a tool for modeling and analyzing the hydrodynamic behavior of biomassas a single material or as part of a mixture in a fluidized bed. The first part of this research focused on the characterization of biomass particles in a fluidized bed and validation of a numerical model with experimental results obtained from pressure measurements and CT and X-ray radiograph images. For a 2D fluidized bed of glass beads, the pressure drop, void fraction and mean bed height expansion were in quantitative agreement between the experiments and simulations using Syamlal-O'Brien and Gidaspow drag models. It was encouraging that the Gidaspow model predictions were in close agreement because the model does not require knowing the minimum fluidization as an input. Ground walnut shells were used to represent biomass because the material fluidizes uniformly and is classified as a Geldart type B particle. Two-dimensional simulations of ground walnut shells were analyzed to determine parameters that cannot easily be measured experimentally. The parametric study for ground walnut shell indicated that the material can be characterized with a medium sphericity (~0.6) and a relatively large coefficient of restitution (~0.85). In the second part of this work numerical simulations of a ground walnut shell fluidizing bed with side air injection were compared to CT data for the gas-solid distribution to demonstrate the quantitative agreement for bed fluidization. The findings showed that 2D simulations overpredicted the fluidized bed expansion and the results did not demonstrate a uniformly fluidizing bed. The 3D simulations compared well for all cases. This study demonstrates the importance of using a 3D model for a truly 3D flow in order to capture the hydrodynamics of the fluidized bed for a complicated flow and geometry. Finally, CFD modeling of pressure fluctuations was performed on sand and cotton-sand fluidized beds operating at inlet velocities ranging from 1.0-9.0Umf with the objective of predicting characteristic features of bubbling, slugging, and turbulent fluidization regimes. It was determined that the fluidized bed can be modeled using MUSCL discretization and the Ahmadi turbulence model. Three-dimensional sand fluidized beds were simulated for different fluidization regimes. Fluidized beds for all the regimes behaved as second-order dynamic systems. Bubbling fluidized beds showed one broad peak with a maximum at 2.6 Hz while slugging and turbulent showed two distinct peaks. It was observed that the peak at low frequency increased in magnitude as the flow transitioned from a slugging to a turbulent fluidization regime. CFD simulations of fluidized beds with the purpose of studying pressure fluctuations have demonstrated to be a useful tool to obtain hydrodynamic information that will help determine the fluidization regime. Prediction of slugging and turbulent fluidization regimes using CFD have not been reported to date. The work presented here is the first of its kind and can be an important advantage when designing a reactor and evaluating different operation conditions without the need to test them in a pilot plant or a prototype.<br>Ph. D.

Fluidized bed reactor technology has been widely adopted within the industry as vital component for numerous manufacturing, power generation and gasification processes due to its enhanced mixing characteristics. Computational modeling of fluidized bed hydrodynamics is a significant challenge that has to be tackled for increasing predictive accuracy. The distributor plate of a fluidized bed is typically modeled using a uniform inlet condition, when in reality the inlet is non-uniform inlet. The regions of bed mass that do not fluidize because of the non-uniform inlet conditions form deadzones and remain static between the jets. A new model based on the mass that contributes to the pressure drop is proposed to model a fluidized bed, and has been investigated for a cylindrical reactor for glass beads, ceramic single solids particles, and glass-ceramic, and ceramic-ceramic binary mixtures. The adjusted mass model was shown to accurately predict fluidization characteristics such as pressure drop and minimum fluidization velocity. The effectiveness of the adjusted mass model was further illustrated by applying it to fluidized beds containing coal, switchgrass, poplar wood, and cornstover biomass particles and coal-biomass binary mixtures. The adjusted mass model was further analyzed for bed expansion heights of different mixtures, and for solids distribution by analyzing the solids volume fraction. The effect of increasing the percent biomass in the mixture was also investigated. To further model the non-uniform inlet condition, two different distributor configurations with 5 and 9 jets was considered for a quasi-2D bed, and simulations were performed in both 2D and 3D. Fluidization characteristics and mixing of the bed were analyzed for the simulation. Furthermore, the deadzones formed due to multiple jet configurations of the distributor are quantified and their distributions over the plate were analyzed.<br>Ph. D.

ANP; FINEP<br>Este trabalho apresenta um estudo sobre parâmetros do sinal de ultra-som que são afetados pelo escoamento bifásico água-ar, muito comuns em diversos processos industriais. Foi utilizado um par de transdutores no modo transmissão-recepção em um duto de acrílico com 54 mm de diâmetro interno. As técnicas utilizadas na análise do sinal foram a medição da velocidade do som por diversos métodos, a análise da energia e da amplitude máxima. Também é proposto o uso da atenuação em banda larga do ultra-som, uma técnica muito comum e utilizada no diagnóstico médico da osteoporose, mas pouco utilizada na indústria. Outra proposta foi utilizar o primeiro vale da onda de ultra-som recebida para normalização do sinal, evitando a necessidade de um sinal referência para a determinação da fração de vazios. É apresentada a metodologia teórica e os resultados dos experimentos que foram realizados em um circuito bifásico instalado no LABPETRO/UNICAMP. O hardware e software do sistema de aquisição de dados foram desenvolvidos no LASCA/UTFPR.<br>This work presents a study of ultrasound signal parameters that are affected by two-phase flow water-air present in several industrial process. A pair of ultrasound transducers in transmissionreception mode has been installed in a 54 mm inner diameter plexiglass pipe. Velocity measurement is calculated by many methods and also energy and maximum amplitude analysis was applied. Additionally, it is proposed a broadband ultrasound attenuation (BUA) based method to measure the void fraction. BUA is a very common method used to diagnoses osteoporosis but underused in industry. Other method based on a signal normalization by the first valley is developed to avoid the use of a reference signal to calibrate the prototype. Theoretical methods and experimental results are described. The results were obtained in a two phase circuit situated in LABPETRO/UNICAMP. The hardware and software of acquisition system were developed in LASCA/UTFPR.

This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.<br>Bachelors<br>Engineering and Computer Science<br>Mechanical Engineering

Heat transfer and pressure drop during condensation of propane flowing through minichannels is investigated in this study. Studies of condensation of hydrocarbons are important for applications in the petrochemical industry. Insights into the mechanisms of propane condensation are required for accurate design of heat transfer equipment for use in hydrocarbon processing. At present, there is very little research on vertical condensation, especially of hydrocarbons, for the tube sizes and flow conditions of interest to the present study. An experimental facility was designed and fabricated to measure the frictional pressure drop and heat transfer coefficients during condensation of propane in plain tubes with an inner diameter of 1.93 mm. Measurements were taken across the vapor-liquid dome in nominal quality increments of 0.25 for two saturation temperatures (47°C and 74°C) and four mass flux conditions (75 – 150 kg m‾² s‾¹). The data were compared to the predictions of relevant correlations in the literature. The data from this study were also used to develop models for the frictional pressure drop and heat transfer coefficient based on the measurements and the underlying condensation mechanisms. These results and the corresponding correlations contribute to the understanding of condensation of hydrocarbons in vertical minichannels.

Orientador: Antonio Carlos Bannwart<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, Instituto de Geociências<br>Made available in DSpace on 2018-08-26T04:52:38Z (GMT). No. of bitstreams: 1 Biazussi_JorgeLuiz_D.pdf: 11756361 bytes, checksum: e163630c268ec8b0c1e2a20bc1bdebc9 (MD5) Previous issue date: 2014<br>Resumo: A bomba centrífuga submersa (BCS) é uma bomba de múltiplos estágios que tem recebido muita atenção nos últimos anos, devido à sua importância para a elevação artificial de petróleo em altas vazões. Como uma parte do sistema de Elevação Artificial, a BCS é geralmente instalada no interior do poço, a fim de aumentar a vazão ou até mesmo viabilizar a produção. A presença de gás livre no fluido na entrada da bomba provoca uma diminuição do ganho de pressão fornecido pela BCS e pode conduzir a instabilidades na curva de ganho de pressão versus vazão. O objetivo deste trabalho é desenvolver e avaliar o desempenho de um modelo de deslizamento para representar o ganho de pressão em uma ampla faixa de vazão de líquido de uma BCS. Para este propósito foram realizados testes experimentais em laboratório para três BCS diferentes que operam com misturas ar - água. Especificamente, o ganho de pressão e a potência de eixo foram medidos em diferentes vazões de líquido, de gás, de pressões de entrada e rotação. Os resultados dos testes de água monofásicos foram interpretados por ajuste dos dados com um modelo de correlação genérico para o ganho de pressão e potência, tentando descrever todos os fenômenos físicos envolvidos no escoamento nos canais rotativos. Os resultados dos testes bifásicos foram discutidos em termos dos efeitos da fração de vazio, da pressão de admissão, da velocidade de rotação e da geometria da bomba. Um modelo de deslizamento para escoamento em bolhas foi proposto para representar o ganho de pressão e também foi utilizado para expressar a potência de eixo. Os dois parâmetros envolvidos no modelo, ou seja, C0 e kb?, foram ajustados aos dados e mostrou a capacidade desta abordagem em capturar as principais tendências das curvas experimentais. O parâmetro de distribuição C0 foi, em todos os casos, significativamente menor do que um, confirmando os resultados de outros autores, em escoamento bifásico descendente em tubos. Além disso, este resultado indica que os perfis de velocidade e de distribuição de fase são distorcidos pelo campo centrífugo e de Coriolis. O parâmetro kb? foi significativo apenas para a bomba radial de menor vazão, o que confirma a ideia de que para altas vazões de líquido, as bolhas de gás são dispersadas através do líquido e o deslizamento torna-se insignificante<br>Abstract: The Electrical Submersible Pump (ESP) is a multiple stage pump which has been receiving a lot of attention in recent years in due to its importance for the Artificial Lift of petroleum at high flow rates. As a part of the AL system, the ESP is often installed inside the well in order to either viabilize the production or increase its flow rate. The presence of free gas within the fluid entering the pump causes a decrease in the head provided by the ESP and may lead to instabilities in the head-capacity curve. The aim of this work is to develop and evaluate the performance of a drift flux model to represent the head in the entire liquid flow rate range of an ESP. For this purpose, experimental performance tests to determine the characteristic curves were performed in laboratory for three different ESPs operating with water and water-air mixtures. Specifically, the head and brakehorsepower were measured at different flow liquid and gas flow rates, inlet pressures and rotation speeds. The results from the single-phase water tests were interpreted by fitting generic correlation models for the head and power to the data, trying to describe all basic phenomena involved in the rotating channel flow. The results from the two-phase runs were discussed in terms of the effects of the mixture composition, intake pressure, rotation speed and pump geometry. A drift flux model for bubbly flow was proposed to represent the head and also used to express the power. The two parameters involved in the model, namely C0 and kb? , were fitted to the data and showed good capability of this approach to capture the main trends of the experimental curves. The distribution parameter C0 was in all cases significantly lower than one, confirming the findings by other authors in two-phase downward pipe flow. Also, this result indicates that the velocity and phase distribution profiles are distorted by both the centripetal and Coriolis fields. The drift parameter kb? was significant for the smallest capacity radial pump only, confirming the idea that at sufficiently high liquid flow rates, the gas bubbles are dispersed through the liquid and drift becomes negligible<br>Doutorado<br>Explotação<br>Doutor em Ciências e Engenharia de Petróleo

Orientador: Antonio Carlos Bannwart<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências<br>Made available in DSpace on 2018-08-22T09:14:58Z (GMT). No. of bitstreams: 1 Varon_MauricioPardo_M.pdf: 5247609 bytes, checksum: ddfee289e17057b479b10f2913e86805 (MD5) Previous issue date: 2013<br>Resumo: O Bombeio Centrífugo Submerso (BCS) é um dos métodos mais importantes de elevação artificial de petróleo, no Brasil e no mundo. A bomba de BCS é acionada por um motor elétrico acoplado diretamente ao eixo da bomba. Comumente, possui também um conjunto de sensores que fazem o monitoramento da operação do motor, além de outras variáveis próprias como, por exemplo, o ganho de pressão gerado pela BCS. Por outro lado, a operação remota do motor na superfície se dá através de um inversor de frequência que fornece, além da rotação, o consumo elétrico da BCS. A medição da vazão de líquido produzida por cada poço é tradicionalmente realizada com instrumentação especializada de alto custo. Dado que o sensor do motor da BCS e o inversor de frequência que a opera já fornecem informações utilizadas para o monitoramento do equipamento e para o gerenciamento do poço, a vazão de líquido local na BCS poderia ser determinada com base em curvas de desempenho previamente levantadas nas condições de operação esperadas. O ganho de pressão gerado pela BCS e a potência elétrica consumida pelo motor que a aciona são as variáveis de desempenho consideradas neste estudo para avaliar a incerteza da vazão de líquido local estimada através da bomba em diversas condições de operação (incluindo escoamento bifásico e viscoso). A avaliação é feita com base na norma API RP 11S2, que estabelece as práticas recomendadas para testes de BCS<br>Abstract: ESP (Electrical Submersible Pump) is one the most important artificial lift methods for oil in Brazil and worldwide. The centrifugal pump is driven by an electric motor directly coupled to the pump shaft. Commonly, also has a set of sensors that monitor the electric motor operation, and other variables themselves, for example, the pressure gain generated by the ESP. Moreover, the remote operation of the equipment at the surface is performed via a frequency inverter that provides, in addition to the rotation, the power consumption of the ESP. Measurement of liquid flow rate produced by each well is traditionally performed with specialized instrumentation costly. As the motor sensor and the frequency inverter that drives the ESP already provide information used for monitoring equipment and for managing the well, the local liquid flow rate in the ESP could be determined based on correlations with these data. The pressure gain generated by the ESP and electrical power consumed by the motor are the considered variables for this study to correlate with the flow rate of fluid produced and to assess the quality of the results by analyzing uncertainties. To achieve this, a series of performance curves are obtained at different operating conditions (including two-phase flow and viscous) to observe how the uncertainty of the results are affected by correlated variables. The assessment is based on the standard API RP 11S2, which establishes best practices for testing BCS<br>Mestrado<br>Explotação<br>Mestre em Ciências e Engenharia de Petróleo

Orientador: Antonio Carlos Bannwart<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-19T20:45:05Z (GMT). No. of bitstreams: 1 MonteVerde_William_M.pdf: 4763246 bytes, checksum: d71320f12abcec340b449d80b2466a83 (MD5) Previous issue date: 2011<br>Resumo: A utilização de bombas centrífugas submersas (BCS) operando com a mistura gás-líquido é comum na indústria de petróleo. Para elevadas vazões de líquido e baixas frações de gás o desempenho da bomba é similar ao escoamento monofásico. No entanto, uma degradação severa no desempenho é observada para elevadas frações de gás. A presença de gás livre no escoamento causa instabilidades na curva de ganho de pressão versus vazão. A curva passa a exibir um ponto de máximo, conhecido como ponto de 'surging', sendo que para vazões abaixo desse ponto, ocorre uma acentuada queda no ganho de pressão e, portanto, na capacidade de bombeamento. O aumento da vazão de gás pode causar o bloqueio da área disponível ao escoamento no rotor da bomba, fazendo com que a vazão seja nula, fenômeno conhecido como 'gas locking'. Portanto, o conhecimento das condições operacionais onde ocorre o surging é de fundamental importância para a operação adequada da bomba. O objetivo deste trabalho é obter as curvas de desempenho (elevação, potência e rendimento) de BCS operando com misturas gás-líquido. Com esse propósito as curvas característica de um protótipo de BCS foram determinadas utilizando a mistura água-ar, com frações volumétricas de gás entre 0 e 10% em diferentes rotações, pressões de sucção e vazões de líquido. O protótipo de BCS foi desenvolvido a partir de uma bomba convencional permitindo a visualização do escoamento no interior da bomba. Um manuseador de gás também foi testado buscando determinar suas características operacionais. Os ensaios foram realizados em uma bancada de testes, onde foram medidas os parâmetros do escoamento (vazões de ar e água, pressão e temperatura na entrada e saída da bomba) e parâmetros mecânicos (torque de velocidade de rotação). Uma severa degradação no desempenho, e consequentemente no rendimento da bomba foram observados devido à presença de gás no escoamento. Os fenômenos de surging e gas locking também foram observados durante os testes. A velocidade de rotação e a pressão de sucção influenciaram a fração volumétrica onde o surging ocorre. O aumento da velocidade de rotação e da pressão de sucção desloca a fração volumétrica critica de gás para valores mais elevados, aumentando a faixa operacional da bomba<br>Abstract: The use of electrical submersible pumps (ESP) under gas-liquid flow is very common in the oil industry. At constant liquid flow rate a dramatic degradation on pump head is observed as gas flow rate increases. Natural instabilities of two-phase flow may cause the centrifugal pump to surge at rather low gas void fraction (GVF), as evidenced by a critical point in the pressure gain x flow rate curve, a phenomenon referenced as 'surging point'. Further increase in GVF may cause the gas to fill most of the pump impeller, making the liquid flow rate to decrease down to zero, a phenomenon known as 'gas locking'. Therefore, knowledge of the conditions for which the pump starts to surge is of utmost importance and can only be understood through experimental investigation. The goal of this work is to present the experimental ESP performance curves (head, brake horsepower and efficiency) when operating with gas-liquid mixtures. For that purpose the characteristic curves were determined for one prototype of ESP, operating with water and two-phase air-water mixtures with GVF ranging from 0 to 10 % at different rotational speed, intake pressure and liquid flow rate. The ESP prototype is designed to make possible the flow visualization inside the pump. The performance of a gas handler was also tested in order to determine their operational characteristics. Tests were carried out on an ESP testing bench, where flow parameters (air and water flow rates, pressure and temperature at the inlet and outlet of the pump) and mechanical parameters (shaft torque and speed) were measured. A significant decrease in pump head, and consequently in pump efficiency, was observed as the air fraction was increased. Phenomena like surging and gas locking were observed during these tests. The rotational speed and intake pressure affect the critical GVF at the surging conditions. Increasing the rotational speed and intake pressure moves de critical GVF to higher values extending the operational range the ESP<br>Mestrado<br>Explotação<br>Mestre em Engenharia de Petróleo

La faible déformabilité et l'accumulation des neutrophiles (globules blancs) dans les capillaires pulmonaires peuvent entraîner des syndromes de détresse respiratoire. Nous étudions le comportement des neutrophiles grâce à un code numérique diphasique de type Volume Of Fluid dans différentes configurations confinées. Les cellules sont représentées successivement par quatre modèles différents : dans un premier temps, nous les modélisons par un fluide newtonien caractérisé par sa viscosité et sa tension de surface. Le noyau très visqueux qu'elles contiennent est pris en compte dans un second temps sous forme d'un solide non-déformable grâce à une méthode de frontières immergées. Puis les effets élastiques sont considérés en modélisant le cytoplasme de la cellule par un fluide visco-élastique d'Oldroyd-B. Enfin, une membrane élastique est introduite autour du cytoplasme afin de séparer le mouvement du cytoplasme de celui du plasma. Nous examinons le comportement des cellules ainsi modélisées dans trois configurations : une géométrie de canaux en croix générant en son centre des écoulements linéaires, comme le dispositif des rouleaux de Taylor, une contraction isolée et un réseau périodique dans lequel la cellule traverse plusieurs contractions successives. Alors que la première configuration permet de placer les cellules dans des écoulements de déformation ou de cisaillement pur, les deux autres géométries se rapprochent davantage des configurations réelles. Les résultats mettent en évidence les différences de comportement de la cellule selon le modèle choisi. L'introduction d'un fluide visco-élastique diminue la viscosité effective des cellules et facilite ainsi leurs déformations et leur entrée dans les contractions géométriques. La membrane en revanche modifie de manière notable la forme des cellules et diminue leurs déformations.