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O interesse em escoamento bifásico líquido-líquido aumentou recentemente, em especial devido às grandes perdas de energia envolvidas no transporte de petróleo, onde comumente uma mistura bifásica óleo-água é deslocada ao longo de grandes distancias. Embora este tipo de escoamento seja comum na indústria, não existem tantos trabalhos na literatura quanto os relacionados ao escoamento gás-líquido. Alguns estudos sobre escoamentos óleo-água reportam uma redução de atrito em dispersões e emulsões em regime turbulento sem adição de qualquer tipo de substancia química, mas a física por trás do fenômeno ainda não é bem compreendida. Neste trabalho, foi estudado o padrão de escoamento disperso óleo-água em tubulação horizontal, visando a obtenção de novos dados experimentais e um melhor entendimento do fenômeno de redução de atrito. Uma série de parâmetros considerados importantes para a caracterização do escoamento foi investigada: queda de pressão, fração volumétrica e sub-padrões de escoamento disperso. Apresentam-se dados de distribuição das fases e fração volumétrica in situ, obtidos através de um moderno sensor intrusivo, do tipo wire-mesh, baseado em medidas de capacitância (permissividade). Câmera de alta velocidade e técnica das válvulas de fechamento rápido foram utilizadas para validar os sinais do sensor. Um modelo prospectivo simplificado foi desenvolvido como uma tentativa de explicar a ocorrência do fenômeno de redução de atrito no padrão disperso óleo-água estudado. O modelo sugere que a presença de uma fina película de água rente a parede hidrofílica/oleofóbica do tubo poderia explicar a diminuição no gradiente de pressão bifásico observada. / The interest in two-phase liquid-liquid flow has increased recently mainly due to the petroleum industry where oil and water are often produced and transported together for long distances and the significant frictional pressure gradient involved. Liquid-liquid flows are present in a wide range of industrial processes; however, they have not been studied as intensively as gas-liquid flows. Drag reduction phenomenon in oil-water flows without the addition of any drag reduction agent has been detected in previous works, but the physics behind the phenomenon is yet not well understood. The aim of the research was to study the dispersed oil-water flow pattern in a horizontal pipe in order to better understand the phenomenon and the obtaining of new experimental data of oil-water dispersed flows. Important issues related to oil-water pipe flow were investigated: pressure drop, volume fraction and flow patterns. Phase distribution and holdup data were obtained by a new wire-mesh sensor based on capacitance (permittivity) measurements. A high-speed video camera and the Quick-Closing-Valves technique were used to compare and validate the signals of the wire-mesh sensor. A simplified mathematical model was proposed to explain the drag reduction phenomenon in the oil-water dispersed flow studied. The model suggests that the presence of a thin water film between the homogenously dispersed flow and the pipe wall could explain the observed decreases of the two-phase pressure gradient.

O interesse em escoamento bifásico líquido-líquido aumentou recentemente, em especial devido às grandes perdas de energia envolvidas no transporte de petróleo, onde comumente uma mistura bifásica óleo-água é deslocada ao longo de grandes distancias. Embora este tipo de escoamento seja comum na indústria, não existem tantos trabalhos na literatura quanto os relacionados ao escoamento gás-líquido. Alguns estudos sobre escoamentos óleo-água reportam uma redução de atrito em dispersões e emulsões em regime turbulento sem adição de qualquer tipo de substancia química, mas a física por trás do fenômeno ainda não é bem compreendida. Neste trabalho, foi estudado o padrão de escoamento disperso óleo-água em tubulação horizontal, visando a obtenção de novos dados experimentais e um melhor entendimento do fenômeno de redução de atrito. Uma série de parâmetros considerados importantes para a caracterização do escoamento foi investigada: queda de pressão, fração volumétrica e sub-padrões de escoamento disperso. Apresentam-se dados de distribuição das fases e fração volumétrica in situ, obtidos através de um moderno sensor intrusivo, do tipo wire-mesh, baseado em medidas de capacitância (permissividade). Câmera de alta velocidade e técnica das válvulas de fechamento rápido foram utilizadas para validar os sinais do sensor. Um modelo prospectivo simplificado foi desenvolvido como uma tentativa de explicar a ocorrência do fenômeno de redução de atrito no padrão disperso óleo-água estudado. O modelo sugere que a presença de uma fina película de água rente a parede hidrofílica/oleofóbica do tubo poderia explicar a diminuição no gradiente de pressão bifásico observada. / The interest in two-phase liquid-liquid flow has increased recently mainly due to the petroleum industry where oil and water are often produced and transported together for long distances and the significant frictional pressure gradient involved. Liquid-liquid flows are present in a wide range of industrial processes; however, they have not been studied as intensively as gas-liquid flows. Drag reduction phenomenon in oil-water flows without the addition of any drag reduction agent has been detected in previous works, but the physics behind the phenomenon is yet not well understood. The aim of the research was to study the dispersed oil-water flow pattern in a horizontal pipe in order to better understand the phenomenon and the obtaining of new experimental data of oil-water dispersed flows. Important issues related to oil-water pipe flow were investigated: pressure drop, volume fraction and flow patterns. Phase distribution and holdup data were obtained by a new wire-mesh sensor based on capacitance (permittivity) measurements. A high-speed video camera and the Quick-Closing-Valves technique were used to compare and validate the signals of the wire-mesh sensor. A simplified mathematical model was proposed to explain the drag reduction phenomenon in the oil-water dispersed flow studied. The model suggests that the presence of a thin water film between the homogenously dispersed flow and the pipe wall could explain the observed decreases of the two-phase pressure gradient.

Dans ce travail, des écoulements liquide-liquide dispersés homogènes (c'est-à-dire sans gradient de concentration) ont été étudiés dans une conduite horizontale de 7.5m de long et de 50mm de diamètre interne. Les expériences ont été réalisées dans une large gamme de paramètres opératoires (vitesses de mélange comprises entre 0.28 et 1.2m/s et concentration volumique en phase dispersée, f, de 0.08 à 0.7). Le facteur de frottement de ces écoulements a été mesuré et modélisé en régime turbulent, intermédiaire et laminaire. Ces différents régimes ainsi que l’effet de la concentration en phase dispersée ont été identifiés à partir des mesures locales de vitesse par une technique de vélocimétrie par image de particules (PIV). Lorsque f=0.56, les dispersions se comportent comme des fluides newtoniens auxquels le concept de viscosité effective peut s’appliquer. Le modèle de viscosité de Krieger et Dougherty (1959) décrit l’ensemble des émulsions formées. Le facteur de frottement mesuré suit les lois de frottement classiques en régime laminaire et turbulent (Hagen-Poiseuille et Blasius respectivement) en fonction du nombre de Reynolds basé sur les propriétés de mélange des émulsions (densité et viscosité). Toutefois, la concentration en phase dispersée induit un retard à l’apparition de la turbulence. En milieu très concentré (f=0.7), la dispersion a un comportement rhéofluidifiant et suit la loi d’Ostwald avec un exposant, n=0.5. Tous ces écoulements ont été étudiés, en détail, par l’analyse locale des vitesses. / Homogeneous dispersed flows have been investigated in a horizontal pipe (7.5m long and 50mm internal diameter) in a wide range of flow parameters (mixture velocity from 0.28 to 1.2m/s and concentration, f, up to 0.7). In this work, the wall friction of this emulsion has been measured and modeled in turbulent, intermediate and laminar regime. The different flow regime and the effect of dispersed phase volume fraction have been determined from the velocity profiles measured by PIV measurements in a refractive index matched medium. When f=0.56, emulsion behaves as newtonian fluid. It was shown that the concept of effective viscosity is relevant to scale the wall friction of the emulsion flow. The effective viscosity follows the classical trend of low inertia suspension of hard spheres (Krieger & Dougherty 1959). The friction factor is described by the classical single phase laws in turbulent and laminar regime (Hagen-Poiseuille and Blasius respectively) as a function of Reynolds number based on mixture properties (density and viscosity). Compared to single phase flow, the transition to turbulence is delayed as dispersed phase fraction is increased. For higher dispersed phase fraction (f=0.7), emulsion behaves as a shear-thinning fluid. Emulsion follows the Ostwald law with an exponent equal to 0.5. All these homogeneous dispersed flow have been studied in details.

Continuous processing in the pharmaceutical and fine chemical industries, particularly in micro/milli-scale reactors, has been a topic of interest in literature in recent years due to the advantages offered over batch reactions. One such advantage is the enhanced transport properties of operating at smaller scales, although the quantification of the transport phenomena is not straightforward when wall and entrance effects cannot be neglected. In the first study presented, various micro-mixer geometries and scales were considered to increase the mixing efficiency in liquid-liquid systems of diverse interfacial tensions for fast reactions. The conditions were varied over different flow regimes; including slug flow, parallel flow, and drop flow. A mass-transfer-limited test reaction was used to evaluate the overall volumetric mass transfer coefficients (Korga) as a function of the average rate of energy dissipation (ε) for each mixer design. The onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers for low interfacial-tension systems (i.e., n-butanol-water). In the drop flow regime for energy dissipation rates of around 20 to 500 W/kg, Korga values ranged from approximatively 0.14 to 0.35 s-1 and 0.004 to 0.015 s-1 for the relatively low and high interfacial-tension (i.e., toluene-water) systems, respectively. The second investigation explored the heat transfer properties of a FlowPlate® system by Ehrfeld Mikrotechnik BTS. First, in a non-reactive system with rectangular serpentine channels (d_h<1mm, 400<Re<2000), a Gnielinski-type model was fit to the internal Nusselt number. Using a silver-based thermal paste between the reactor and heat transfer fluid plates proved to reduce the external resistance to heat transfer by ~70%, yielding overall heat transfer coefficients of ~2200 [W/(m^2 K)]. Secondly, a Grignard reaction was highlighted as a test reaction to compare different reactors’ localized heat transfer characteristics (i.e., hotspot formation) with various micro-mixer geometries, materials, injection ports, and channel scales. Lastly, a case study of four reactions utilized the fourth Damköhler number to determine a maximum channel diameter that would remove sufficient heat to avoid hotspot formation. Each of these studies provides insight to aid in the proper selection of a reactor for a given set of physical properties and reaction kinetics/enthalpies.

O escoamento líquido-líquido, em especial o escoamento óleo-água, vem atraindo a atenção de pesquisadores devido à alta demanda pelo combustível fóssil no atual cenário petrolífero mundial e nacional. Os desafios tecnológicos colocados pelas descobertas de reservas de óleos pesados e altamente viscosos consideram, em especial, a preocupação por minimizar as perdas energéticas nas linhas. Emulsões inversas ou dispersões óleo-em-água, na qual o óleo se encontra disperso de maneira uniforme em água, caracteriza-se pela baixa viscosidade aparente, tornando-se um tipo de emulsão desejável em algumas etapas do transporte de petróleo. Esses fatos tornam essencial o estudo deste tipo de padrão para o dimensionamento e operação ótima de dutos de produção de petróleo. Contudo, não existe ainda um número abrangente de trabalhos sobre padrão disperso líquido-líquido, ao comparar com escoamento em fases separadas. Trabalhos sobre dispersões têm reportado redução de atrito sem a adição de substâncias químicas em regime turbulento. No entanto, não há ainda um entendimento satisfatório do fenômeno. Na maioria dos trabalhos, sendo quase todos realizados com óleos leves e pouco viscosos, a redução é reportada em dispersões água-em-óleo, com escassos trabalhos reportando o fenômeno em dispersões óleo-em-água. A pesquisa realizada tratou do estudo experimental e teórico de dispersões óleo-em-água em tubulações. O escoamento foi caracterizado a partir da obtenção de dados de holdup, gradiente de pressão por fricção, distribuição das fases e padrão de escoamento. Uma teoria foi proposta para explicar a redução de atrito detectada neste trabalho, baseada na existência de um filme fino de água que escoa em contato com a parede do tubo, a baixos números de Reynolds, evitando o contato direto do núcleo turbulento (mistura bifásica) com a parede do tubo. O referido filme líquido foi detectado e quantificado utilizando-se técnica visual. Além disso, um modelo dinâmico baseado na teoria de lubrificação hidrodinâmica foi desenvolvido como tentativa de explicar a formação do filme líquido parietal no escoamento turbulento de dispersões óleo-água. / Liquid-liquid flow, especially oil-water flow, has attracted the attention of researchers due to the high demand for petroleum in the current global scenario. The discovery of reserves of heavy and highly viscous oils creates new challenges which are mainly concerned with reducing the significant pressure drop in pipes. Inverse emulsion or oil-in-water dispersions in which the oil is dispersed in water is characterized by its low effective viscosity, making it a desirable type of emulsion in some steps of oil production. These facts make the study of dispersed liquid-liquid flow essential for the design and optimal operation of oil pipelines. However, the studies on such flow pattern are scanty in comparison to those on separate flows, as stratified and annular flow patterns. Drag reduction in oil-water turbulent flow without the addition of any chemical substance has been reported in some studies. This phenomenon has received increasing attention in recent years, because there is not a satisfactory understanding of its dynamics yet. Most studies, almost all using light oils, report drag reduction in dispersion of water-in-oil, with few studies reporting the phenomenon in oil-in-water dispersions. This research comprises an experimental and theoretical study on oil-in-water dispersions in pipes. Pressure gradient, holdup, phase distribution and flow patterns data were obtained to characterize the two-phase flow. A theory was proposed to explain the drag reduction detected in this work, based on the existence of a thin water film flowing in contact with the pipe wall at low Reynolds numbers, avoiding contact between the turbulent core (mixture) and the pipe wall. The liquid film was detected and quantified using visual technique. In addition, a dynamic model based on the hydrodynamic lubrication theory was developed as an attempt to explain the formation of the liquid film.

O escoamento líquido-líquido, em especial o escoamento óleo-água, vem atraindo a atenção de pesquisadores devido à alta demanda pelo combustível fóssil no atual cenário petrolífero mundial e nacional. Os desafios tecnológicos colocados pelas descobertas de reservas de óleos pesados e altamente viscosos consideram, em especial, a preocupação por minimizar as perdas energéticas nas linhas. Emulsões inversas ou dispersões óleo-em-água, na qual o óleo se encontra disperso de maneira uniforme em água, caracteriza-se pela baixa viscosidade aparente, tornando-se um tipo de emulsão desejável em algumas etapas do transporte de petróleo. Esses fatos tornam essencial o estudo deste tipo de padrão para o dimensionamento e operação ótima de dutos de produção de petróleo. Contudo, não existe ainda um número abrangente de trabalhos sobre padrão disperso líquido-líquido, ao comparar com escoamento em fases separadas. Trabalhos sobre dispersões têm reportado redução de atrito sem a adição de substâncias químicas em regime turbulento. No entanto, não há ainda um entendimento satisfatório do fenômeno. Na maioria dos trabalhos, sendo quase todos realizados com óleos leves e pouco viscosos, a redução é reportada em dispersões água-em-óleo, com escassos trabalhos reportando o fenômeno em dispersões óleo-em-água. A pesquisa realizada tratou do estudo experimental e teórico de dispersões óleo-em-água em tubulações. O escoamento foi caracterizado a partir da obtenção de dados de holdup, gradiente de pressão por fricção, distribuição das fases e padrão de escoamento. Uma teoria foi proposta para explicar a redução de atrito detectada neste trabalho, baseada na existência de um filme fino de água que escoa em contato com a parede do tubo, a baixos números de Reynolds, evitando o contato direto do núcleo turbulento (mistura bifásica) com a parede do tubo. O referido filme líquido foi detectado e quantificado utilizando-se técnica visual. Além disso, um modelo dinâmico baseado na teoria de lubrificação hidrodinâmica foi desenvolvido como tentativa de explicar a formação do filme líquido parietal no escoamento turbulento de dispersões óleo-água. / Liquid-liquid flow, especially oil-water flow, has attracted the attention of researchers due to the high demand for petroleum in the current global scenario. The discovery of reserves of heavy and highly viscous oils creates new challenges which are mainly concerned with reducing the significant pressure drop in pipes. Inverse emulsion or oil-in-water dispersions in which the oil is dispersed in water is characterized by its low effective viscosity, making it a desirable type of emulsion in some steps of oil production. These facts make the study of dispersed liquid-liquid flow essential for the design and optimal operation of oil pipelines. However, the studies on such flow pattern are scanty in comparison to those on separate flows, as stratified and annular flow patterns. Drag reduction in oil-water turbulent flow without the addition of any chemical substance has been reported in some studies. This phenomenon has received increasing attention in recent years, because there is not a satisfactory understanding of its dynamics yet. Most studies, almost all using light oils, report drag reduction in dispersion of water-in-oil, with few studies reporting the phenomenon in oil-in-water dispersions. This research comprises an experimental and theoretical study on oil-in-water dispersions in pipes. Pressure gradient, holdup, phase distribution and flow patterns data were obtained to characterize the two-phase flow. A theory was proposed to explain the drag reduction detected in this work, based on the existence of a thin water film flowing in contact with the pipe wall at low Reynolds numbers, avoiding contact between the turbulent core (mixture) and the pipe wall. The liquid film was detected and quantified using visual technique. In addition, a dynamic model based on the hydrodynamic lubrication theory was developed as an attempt to explain the formation of the liquid film.

An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness. A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters. Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.

Celui-ci a pour objectif de valider l'ensemble des modèles physiques utilisés dans un code de simulation numérique pour simuler un écoulement de type annulaire dispersé en conduite rencontré lors d'une procédure de lavage à eau utilisé dans les raffineries. Pour ce faire une banque de données expérimentale est mise en place sur des configurations représentatives de celles utilisées en condition industrielle. La géométrie retenue comporte une zone horizontale d'injection rectiligne avec un injecteur central, suivi d'un coude à 90° situé dans un plan vertical. Différentes conditions expérimentales permettent d'étudier l'influence de la vitesse du gaz, de la condition d'injection du brouillard et de la pression sur les différents processus physiques. Ces résultats comprenant des visualisations du brouillard et du film pariétale, des mesures de taille et de distribution de gouttes,des mesures de débit et d'épaisseur de film, sont analysés pour faire ressortir les principaux mécanismes d'interaction entre le gaz et la phase dispersée, le gaz et le film liquide pariétal et la phase dispersée et le film pariétal. En parallèle, des premières simulations, avec une approche RANS, sont réalisées avec le code CEDRE de l'ONERA et les résultats sont confrontés aux mesures. / This work has been realised within a CIFRE contract with TOTAL. Its aim was to validate all the physical models used in a computation, which simulates an annular dispersed flow through a pipe used in a water washing process in refinery plants. That is why, a whole set of data has been gathered using experimental boundary conditions which are representative to those used in industrial configurations. The geometry is made of a horizontal pipe with a centred nozzle followed by a 90º elbow in the vertical plane. Several experimental boundary conditions enable one to study the influence of the gas velocity, the type of the spray injection and the pressure on the different physical phenomena. These results including spray and liquid film visualisations, droplets distribution and size measurements as well as liquid film thickness and mass flow measurements were analysed in order to extract the main interaction mechanism between the gas and the dispersed phase, the gas and the liquid film, and the dispersed phase and the annular liquid film. Meanwhile, simulations using a RANS approach were realized with the ONERA code named CEDRE and its results were compared to the gathered measurements.