Orientador: Osvaldir Pereira Taranto / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-06T17:24:34Z (GMT). No. of bitstreams: 1 Nitz_Marcello_D.pdf: 15161394 bytes, checksum: 9df0e832ac9d2f50417fc4a6f39efe86 (MD5) Previous issue date: 2006 / Resumo: O presente trabalho teve como objetivos principais analisar as operações de secagem e recobrimento desenvolvidas em leito pulso-fluidizado. Estudos fluidodinâmicos realizados com feijão, trigo e peneira molecular permitiram a comparação desta técnica com a fluidização convencional, principalmente no que concerne à queda de pressão no leito e às variáveis que a influenciam. Para todos os casos, a queda de pressão mostrou uma relação de dependência com a velocidade superficial do gás semelhante àquela que se verifica nos equipamentos de fluidização convencional. Ensaios de secagem com os mesmos materiais permitiram estudar o nível de influência das variáveis operacionais, como vazão e temperatura do ar, freqüência de pulsação do leito e carga de material processado, nos resultados obtidos. Trigo e feijão são materiais cuja secagem é limitada pela difusão da umidade. Para eles, a intermitência da corrente gasosa proporcionada pela pulsação não influenciou a cinética da secagem. As curvas de secagem de feijão com regime pulsante e com fluidização convencional ficaram praticamente sobrepostas. A peneira molecular, por sua vez, apresenta um período inicial de secagem com velocidade constante. Nessa fase em que a remoção da umidade é controlada pela evaporação superficial, a fluidização convencional apresentou taxa de secagem maior do que no regime pulsante. Comparando-se condições de fluidização pulsante entre si, percebeu-se influência da freqüência de pulsação, da temperatura do ar e da vazão de gás sobre a velocidade de secagem. No que diz respeito à operação de recobrimento, grânulos contendo o fármaco teofilina foram revestidos com uma suspensão comercial à base de polivinilacetato produzida pela BASF, chamada Kollicoat. A película formada por esse polímero tem a característica de oferecer uma barreira à liberação da droga, com permeabilidade independente do pH. Seguindo um planejamento fatorial completo, a velocidade de liberação da teofilina foi analisada em função do diâmetro da partícula, da vazão de suspensão empregada nos ensaios, da freqüência de pulsação do leito e do tempo de atomização. Todas as variáveis mostraram efeito significativo sobre o perfil de liberação - a freqüência em menor grau. Foi possível obter modelos empíricos que relacionam o teor de droga liberada em função das variáveis independentes citadas / Abstract: The present work aimed to study the coating and drying operations perfonned in a pulsedfluid bed piece of equipment. Based on fluid-dynamic studies perfonned with beans, wheat and molecular sieves, comparisons could be made between conventional and pulsed fluidization, focusing on values of pressure drop and the variables that might affect it. The graphical profile of the relation between pressure drop and the superficial velocity of the gas resembles that of ordinary fluidization. Drying tests were perfonned with the same materials. Drying kinetics analysis showed the influences of airflow rate, inlet temperature of air and frequency of pulsation on the drying rate of beans, wheat and molecular sieves. Wheat and beans are material whose rate of drying is controlled by the internal movement of water. The molecular sieves, on the other hand, are porous materiaIs and their drying rate is limited by the moisture surface evaporation. For beans and wheat, the frequency of pulsation did not affect the drying rate. For these two materials, the intermittence provided by the pulsed flow did not affect the moisture removal rate. Drying of beans was also perfonned under conventional fluidization and the drying curve was quite the same as the one obtained with pulsed fluidization in the same temperature. The molecular sieve presents a first period of constant drying rate. As a consequence, conventional fluidization presented a higher drying rate than the one achieved with pulsed flow. Comparisons among different pulsed fluidization conditions showed that frequency, temperature and airflow rate exerted influence on the drying rate. As far as coating is concerned, granules with the theophylline drug were coated with a commercial suspension called Kollicoat, manufactured by BASF, which consists of polyvinylacetate. The film provided by this polymer offers a pH-independent barrier for mass transporto Following a full factorial design, the influences of particle diameter, suspension flow rate, pulsation frequency and atomizing time on the in vitro drug release rate were analyzed. All variables showed some influence on the drug release profile. However, the influence of frequency was subtle. Empirical models and response surfaces were obtained to relate the process variables to the drug release profiles / Doutorado / Engenharia de Processos / Doutor em Engenharia Química

Orientador: Rosiane Lopes da Cunha / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-19T15:16:51Z (GMT). No. of bitstreams: 1 Vilela_JoiceAlinePires_M.pdf: 1796773 bytes, checksum: 34d2e3b8b4543d7ea7cce06e84d31138 (MD5) Previous issue date: 2012 / Resumo: A encapsulação de muitos compostos bioativos, como vitaminas, bactérias probióticas e antioxidantes ajuda na incorporação, proteção, e entrega do bioativo em sítio específico, porém a eficiência da matriz carreadora depende da sua composição e processo de fabricação. Com este intuito, a viabilidade de produção e as características finais de microgéis de gelana formados por extrusão e posterior gelificação iônica foram estudadas. Micropartículas, com tamanho médio entre 70-120 ?m, foram produzidas sob condições amenas de temperatura e concentração, utilizando um processo de atomização seguido de gelificação em soluções de cloreto de cálcio (CaCl2), cloreto de potássio (KCl) ou quitosana. O tamanho das partículas mostrou-se mais dependente das condições de processo (geometria do bico aspersor e velocidade de ar) que das propriedades da solução biopolimérica. No entanto, o aumento da concentração de gelana levou a maior esfericidade dos microgéis obtidos. Com relação aos agentes gelificantes, as micropartículas com gelificação induzida por CaCl2 apresentaram formato mais esférico e maior estabilidade que as partículas formadas a partir de KCl. A obtenção de micropartículas de gelana recobertas com quitosana foi possível somente através de um processo em duas etapas. Na primeira etapa, a gelana foi gelificada através da difusão salina (CaCl2 ou KCl) e posteriormente, as partículas formadas foram recobertas com quitosana. A presença da camada externa de quitosana teve influência na resistência das partículas às condições simuladas da digestão. As partículas estudadas, com ou sem recobrimento de quitosana, resistiram à digestão gástrica, mas na digestão entérica as partículas recobertas com quitosana apresentaram menor grau de fragmentação que as partículas contendo somente gelana. Assim, foi demonstrado que a produção de microgéis formados por interação entre dois biopolímeros de cargas opostas melhorou a eficiência das partículas como material de parede sendo este um potencial veículo de compostos bioativos / Abstract: The encapsulation of many bioactive compounds such as vitamins, antioxidants and probiotic bacteria allows the incorporation, protection, and delivery of bioactive on a specific site, but the efficiency of carrier matrix depends on its composition and manufacturing process. To this aim, the feasibility of production and the final characteristics of the gellan microgels obtained by extrusion process followed by ionic gelation were studied. Microparticles, with average size among 70-120 ?m, were produced under mild conditions of temperature and concentration using an atomization process followed by gelation induced by calcium chloride (CaCl2), potassium chloride (KCl) or chitosan solutions. The particle size was more dependent on process conditions (nozzle geometry and air velocity) than the properties of the biopolymeric solution. However, the increase in gellan concentration led to more spherical microgels. In relation to hardening agents, the microparticles with gelation induced by CaCl2 showed more spherical shape and greater stability than the particles formed by KCl. Gellan microparticles coated with chitosan was possible to obtain only through a two-step process. In the first step, the gellan microgels were obtained through salt diffusion (KCl or CaCl2) and the particles obtained were subsequently coated with chitosan. The presence of the outer layer of chitosan exerted effect on the resistance of the particles to the simulated digestion process. All particles studied, with or without a coating of chitosan, resisted to the gastric digestion, however the chitosan coated particles showed a lower degree of fragmentation than the particles containing only gelan when subjected to the enteric digestion step. Therefore the results obtained showed that the microgels formed by interaction between two oppositely charged polymers improved the efficiency of particles as wall material, showing a great potential as bioactive compounds carrier / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

Orientador : Rosiane Lopes da Cunha / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-04T02:36:29Z (GMT). No. of bitstreams: 1 Sato_AnaCarlaKawazoe_M.pdf: 1482214 bytes, checksum: 6d3d861dcc6236f5bb792d5187073a03 (MD5) Previous issue date: 2005 / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

The main aim of this project is to model the effects of varied injection parameters on the gas dynamics and droplet dynamics of the HVSFS and SP- HVOFS processes for improving the droplet breakup and evaporation to enhance the nanoparticles heating and deposition efficiency. Thermal spraying processes are widely used to generate thermal-, corrosion-, and wear-resistant layers over the machine parts, to increase the durability of the equipment under severe environmental conditions. The liquid feedstock is used to achieve nanostructured coatings. It is used either in the form of a suspension or a solution precursor. The suspension is a mixture of solid nanoparticles suspended in a liquid medium consisting, for instance, of water, ethanol, or isopropanol. This dispersion mechanism in a liquid carrier provides adequate flowability to the nanoparticles, which cannot be handled by conventional gas- based feeding systems, whereas the solution precursor is mixed at the molecular level; hence, more uniform phase composition and properties are expected in the sprayed coatings as compared to the suspension and conventional powder spraying. Firstly, experiments are conducted to analyse the effects of different precursor concentrations, solvent types and injection nozzles on the size and morphology of synthesized nanoparticles. The results indicate that the particle size increased with increasing precursor concentration due to the variations in the physical properties of the mixture solution. The higher precursor concentrations had an adverse effect on the droplet atomization and evaporation process that led to bigger size particle formation. The use of aqueous solvent has some limits and with higher precursor concentration the surface tension increases that resulted in the reduction of droplets’ disintegration, and thus bigger size precursor droplets generate larger nanoparticles. A mixture of aqueous-organic solvents and pure organic precursors are preferred to improve the process efficiency of the nanoparticles size and morphology. Furthermore, the nanoparticles size can be controlled by using liquid feedstock atomization before injecting into the HVOF torch. A new effervescent injection nozzle is designed and compared to different types of existing injection nozzles, to see the variations in the droplet disintegration, and its effects on the performance of the HVOF torch processes. It is detected that the atomization would result in smaller size particles with homogeneous morphology. In a numerical study, different droplet injection types are analysed to see their effects on the gas and droplet dynamics inside the HVOF torch. The group-type injection (GTI) and effervescent-type atomization (ETI) are used effectively to overcome the heat losses and delays in the droplet evaporation. These approaches reduce the thermal and kinetic energy losses in the suspension-fed-HVOF torch, thereby improving the coating formation. The effects of using multicomponent water-ethanol mixture injection in the HVOF torch are also modelled, and its impact on the droplet breakup and evaporation are studied. The organic solvents have a low heat of vaporization and surface tension, and can effectively be used in the HVOF spraying process over the water-based solvents. Furthermore, nanoparticles are suspended in the liquid feedstock and injected into the HVOF torch. The effect of increasing nanoparticles’ concentration in the feedstock and its consequence on the gas dynamics, droplet breakup and evaporation are analysed. The augmentation in the nanoparticles loading in the suspension droplets can decrease the droplet breakup and evaporation rate because the required heat of vaporization increases significantly. Moreover, the size of injection droplet affects the droplet fragmentation process; bigger sized droplets observed a delay in their evaporation that resulted in coating porosity. The results suggest that smaller droplet sizes are preferred in coating applications involving a higher concentration of nanoparticles with high melting point. Further, the gas flow rates (GFRs) are regulated to control the droplet dispersion, atomization and evaporation inside the solution precursor fed-HVOF torch. The size of the droplet diameter is decreased by an increment in the GFR, as higher combustion rates increase the combustion flame enthalpy and kinetic energy. Moreover, the increase in the oxygen/fuel flow rates dilutes the injected precursor. It reduces ZrO2 concentration in the process and decreases the rate of particle collision; as a result, non-agglomerated nanoparticles can be obtained.

This paper investigated the effects of swirl number and momentum ratio on the atomization and mixing performance of Swirl-Venturi Lean Direct Injection technology. Mie scattering of liquid water, was used to identify the location of water droplets in a cross section of the injector spray. Experiments were performed with three air swirlers with vane angles of 45, 52 and 60 degrees. The swirl number varied from 0.58 to 1.0 and air-to-liquid ratios from 15.8 to 35.6. A transition was observed in the liquid spray distribution for the 52 degree case, which unexpectedly produced twice as much signal than the 45 and 60 degree cases. The main cause of this increased signal may be due to instabilities in the flow when transitioning from low to high swirl states. The results from investigation of swirl number it was found that the spray pattern for is sensitive to swirl intensity. Two flow states were observed for a lower and higher swirl flow as well as a transition state that occurred with the lower swirl state. This work may aid in the specific inquiry of physical mechanisms relating to the effect of flow states on spray distribution. It is found that improved atomization and mixing performance are a result of increase in swirl number.

[EN] The main objective of this work is the modeling of diesel sprays under engine conditions, including the atomization, transport and evaporation processes pivotal in the diesel spray formation and its development. For this purpose, an Eulerian single fluid model, embedded in a RANS environment, is implemented in the CFD platform OpenFOAM. The modeling approach implemented here is based on the ⅀-Y model. The model is founded on the assumption of flow scales separation. In actual injection systems, it can be assumed that the flow exiting the nozzle is operating at large Reynolds and Weber numbers and thus, it is possible to assume a separation of features such as mass transport (large scales) from the atomization process occurring at smaller scales. The liquid/gas mixture is treated as a pseudo-fluid with variable density and which flows with a single velocity field. Moreover, the mean geometry of the liquid structures can be characterized by modeling the mean surface area of the liquid-gas interphase per unit of volume. Additionally, an evaporation model has been developed around the particular characteristics of the current engine technologies. This means that vaporization process is limited by fuel-air mixing rate and fuel droplets evaporate as long as there is enough air for them to heat up and vaporize. Consequently, the evaporation model is based on the Locally Homogeneous Flow (LHF) approach. Under the assumption of an adiabatic mixing, in the liquid/vapor region, the spray is supposed to have a trend towards adiabatic saturation conditions and to determine this equilibrium between phases Raoult's ideal law is considered. Finally, the spray model is coupled with an advanced combustion model based on approximated diffusion flames (ADF), which reduces the computational effort especially for complex fuels and is a natural step for modeling diesel sprays. First, the model is applied to a basic external flow case under non-vaporizing conditions, extremely convenient due to both the experimental database available and the symmetric layout which allows important simplification of the modeling effort. Good agreement between computational results and experimental data is observed, which encourages its application to a more complex configuration. Secondly, the model is applied to the "Spray A" from the Engine Combustion Network (ECN), under non-vaporizing conditions, in order to reproduce the internal structure of diesel sprays as well as to produce accurate predictions of SMD droplets sizes. Finally, vaporizing "Spray A" studies are conducted together with the baseline reacting condition of this database. The calculated spray penetration, liquid length, spray velocities, ignition delay and lift-off length are compared with experimental data and analysed in detail. / [ES] El objetivo principal de este trabajo es el modelado de chorros diésel en condiciones de motor, incluyendo los fenómenos de atomización, transporte y evaporación fundamentales en la formación y desarrollo del chorro. Para este fin, se implementa un modelo de spray euleriano de tipo monofluido en un entorno RANS en la plataforma CFD OpenFOAM. El enfoque de modelado aplicado aquí sigue la idea de un modelo del tipo ⅀-Y. El modelo se fundamenta en la hipótesis de separación de escalas del flujo. En los sistemas de inyección actuales, es posible asumir que el flujo que sale de la tobera opera a altos números de Reynolds y Webber y por tanto, es posible considerar la independencia de fenómenos como el transporte de masa (grandes escalas del flujo) de los procesos de atomización que ocurren a escalas menores. La mezcla líquido/gas se trata como un pseudo-fluido con densidad variable y que fluye según un único campo de velocidad. Además, la geometría promedio de las estructuras de líquido se puede caracterizar mediante el modelado de la superficie de la interfase líquido/gas por unidad de volumen. Completando el modelo de chorro, se ha desarrollado un modelo de evaporación alrededor de las características particulares de las tecnologías actuales de los motores. Esto supone que el proceso de evaporación está controlado por mezcla aire-combustible y las gotas de combustible se evaporan siempre que exista suficiente aire para calentarlas y evaporarlas. Debido a esto, el modelo de evaporación implementado está basado en el enfoque de Flujos Localmente Homogéneos (LHF). Considerando una mezcla adiabática, en la región líquido/vapor, se supone que el chorro tiende a las condiciones adiabáticas de saturación y para determinar este equilibrio entre fases, se utiliza la ley ideal de Raoult. Finalmente, el modelo de chorro se acopla con un modelo avanzado de combustión basado en llamas de difusión aproximadas (ADF), que reduce el coste computacional especialmente para combustibles complejos y supone el paso lógico en el desarrollo del modelo para simular chorros diesel. En primer lugar, el modelo se aplica al cálculo de un caso básico de flujo externo no evaporativo, muy adecuado tanto por la extensa base de datos experimentales disponible como por la simetría geométrica que presenta, permitiendo una importante simplificación de la simulación. Los resultados obtenidos presentan un buen acuerdo con los experimentos, lo cual estimula su aplicación en configuraciones más complejas. En segundo lugar, el modelo se aplica al cálculo del "Spray A" del Engine Combustion Network (ECN), no evaporativo, para reproducir la estructura interna del chorro diesel así como predecir tamaños de gota (SMD) de forma precisa. Finalmente, se realizan estudios evaporativos del "Spray A" junto con la condición nominal reactiva de esta base de datos. La penetración de vapor, la longitud líquida, velocidad, el tiempo de retraso y la longitud de despegue de llama calculados se comparan con los datos experimentales y se analizan en detalle. / [CAT] L'objectiu principal d'aquest treball és el modelatge de dolls dièsel en condicions de motor, incloent els fenòmens d'atomització, transport i evaporació fonamentals en la formació i desenvolupament del doll. Amb aquesta finalitat, s'implementa un model de doll eulerià de tipus monofluid en un entorn RANS a la plataforma CFD OpenFOAM. L'enfocament de modelatge aplicat ací segueix la idea d'un model del tipus ⅀-Y. El model es fonamenta en la hipòtesi de separació d'escales del flux. En els sistemes d'injecció actuals, és possible assumir que el flux que surt de la tovera opera a alts nombres de Reynolds i Webber, i per tant és possible considerar la independència de fenòmens com el transport de massa (grans escales del flux) dels processos d'atomització que ocorren a escales menors. La mescla líquid / gas es tracta com un pseudo-fluid amb densitat variable i que flueix segons un únic camp de velocitat. A més, la geometria mitjana de les estructures de líquid es pot caracteritzar mitjançant el modelatge de la superfície de la interfase líquid / gas per unitat de volum. Completant el model, s'ha desenvolupat un model d'evaporació al voltant de les característiques particulars de les tecnologies actuals dels motors. Això suposa que el procés d'evaporació està controlat per la mescla aire-combustible i les gotes de combustible s'evaporen sempre que hi hagi suficient aire per escalfar i evaporar. A causa d'això, el model d'evaporació implementat està basat en el plantejament de fluxos Localment Homogenis (LHF). Considerant una mescla adiabàtica, a la regió líquid / vapor, se suposa que el doll tendeix a les condicions adiabàtiques de saturació i per determinar aquest equilibri entre fases, s'utilitza la llei ideal de Raoult. Finalment, el model de doll s'acobla amb un model avançat de combustió basat en flamelets de difusió aproximades (ADF), que redueix el cost computacional especialment per a combustibles complexos i suposa el pas lògic en el desenvolupament del model per simular dolls dièsel. En primer lloc, el model s'aplica al càlcul d'un cas bàsic de flux extern no evaporatiu, molt adequat tant per l'extensa base de dades experimentals disponible com per la simetria geomètrica que presenta, permetent una important simplificació de la simulació. Els resultats obtinguts presenten un bon acord amb els experiments, la qual cosa estimula la seva aplicació en configuracions més complexes. En segon lloc, el model s'aplica al càlcul del "Spray A" no evaporatiu de la xarxa Engine Combustion Network (ECN), per reproduir l'estructura interna del doll dièsel així com predir mides de gota (SMD) de forma precisa. Finalment, es realitzen estudis evaporatius del "Spray A" juntament amb la condició nominal reactiva d'aquesta base de dades. La penetració de vapor, la longitud líquida, velocitat, el temps de retard i la longitud d'enlairament de flama calculats es comparen amb les dades experimentals i s'analitzen en detall. / Pandal Blanco, A. (2016). Implementation and Development of an Eulerian Spray Model for CFD simulations of diesel Sprays [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68490 / TESIS

This diploma thesis deals with matte coatings for optical 3D scanning. The aim of this thesis is to find a method of spraying the mixture of TiO2 and ethanol that would provide layer thickness beyond the measurable range of the 3D scanner. A spray gun allowing deposition of atomized mixture was design. The coatings created by this gun and by airbrush gun, which is commonly used for this purpose, were compared. The matting effect, thickness and the influence of used TiO2 particles were investigated in the coatings. The paper shows method of applying coatings that ensure sufficient matting of the surface for scanning purposes, and simultaneously have thicknesses that should not affect scanning results.

Master thesis focused on the research of the effervescent atomizers. Effervescent atomizers belong to a group of two-phase atomizers, which are often used in combustion applications. Right there in combustion applications, the degree of the stability sprays has a significant impact on combustion efficiency and exhaust gas emissions. The main aim of this work was to asses the level of spray unsteadiness depending on the atomizer design and its operating mode. The effect of construction was studied on the diameter and length of mixing chamber, and then on the size, number and location of aeration holes. Seventeen specific variants of the atomizer were constructed by different combinations of these design parameters. Each of these variants was measured in three operating modes, which were represented by a liquid pressure at the inlet to the atomizer and gas-to-liquid mass flow ratio (GLR). To evaluate the level of spray unsteadiness was used a methodology, which compares the ideal element´s distribution into the interparticle time bin, defined for the ideal (stable) spray, with the experimentally observed distribution. The laser measurement system P/DPA (Phase Doppler Particle Analyzer) was used to determine the experimental interparticle distribution. The result of the comparison of the ideal and the experimental distribution was the parameter , which expresses the level of spray unsteadiness for a specific atomizer and operating mode. With that parameter it was possible to compare the individual atomizers and determinate to the benefit of various construction´s correction of the atomizer. The results showed the recommendation for the modifications of the atomizer, creating a spray with a minimum level of spray´s unsteadiness. For the surveyed atomizer and his individual costruction´s variations the drawing was made.

Le processus d’atomisation est important pour la performance des moteurs à combustion interne. Grâce à un injecteur, le carburant liquide est admis dans la chambre de combustion et se divise en gouttelettes. Plus petites les gouttes, plus rapide leurs évaporation et meilleur le mélange air-carburant. Une meilleure combustion pourrait être obtenue, avec faibles émissions polluantes. La qualité de l’atomisation est influencée principalement par la géométrie de l’injecteur et les conditions opératoires qui forment la structure de l’écoulement interne, la turbulence, le profil de vitesse à la sortie de l’injecteur, la cavitation, etc. Tous ces aspects sont déterminants pour la rupture de l’écoulement externe. Un autre paramètre clé pour optimiser le processus d’atomisation est les propriétés physiques des carburants. On pense, parmi autres, à la tension de surface dynamique contrôlée par la diffusion des surfactants sur l’interface liquide-gaz ou à la viscosité extensionnelle qui rend un liquide plus résistant à l’étirement, influençant donc la rupture. Les effets de la géométrie de l’injecteur, les conditions opératoires et les propriétés physiques des liquides sur l’atomisation sont inter-dépendents. Les analyses expérimentales nous aident à comprendre les mécanismes impliquant et leurs interactions. D’une part, elles sont utiles pour les simulations numériques qui devraient être réalisées suivant la configuration considérée. D’autre part, les critères quantitatifs pourraient être établis afin de valider les résultats numériques. En suivant cette méthodologie de recherche, nous souhaiterons étudier l’atomisation d’une nappe liquide turbulente produite par un injecteur triple-disque. Les mesures expérimentales fournissent les images de la nappe, utilisées comme l’entrée d’une approche multi-échelle. Nous étudions, grâce à la dernière, les comportements de la nappe, des ligaments qui apparaissent à ses bords et des gouttelettes. De plus, deux méthodes de frontières immergées sont développées pour résoudre en même temps l’écoulement interne et le processus d’atomisation. Nous réalisons deux applications, la première pour un jet liquide éjecté par un injecteur cylindrique et la deuxième pour une nappe plane produite par un injecteur triple-disque. / Liquid fuel atomization is crucial for the performance of internal combustion engines. Through an injector, the liquid is delivered into the combustion chamber and breaks down into droplets. The finer the drops, the quicker their evaporation and the more proper their mixing with air. A proficient combustion could hence be expected, with low pollutant emissions. Atomization quality is primarily affected by the injector design and the operating conditions which shape the internal flow structure, the turbulence level, the velocity profile at the nozzle outlet, the cavitation and so forth. All these features are determinants of the breakup of the external liquid flow. Another key parameter to optimize the atomization process is the fuel physical properties. One can think of, among others, the dynamic surface tension controlled by the diffusion of the surfactants on the liquid-gas interface or the extensional viscosity which makes a liquid to become more resistant to the stretching, thereby affecting the breakup. Effects of the injector design, the operating conditions and the liquid properties on the atomization are inter-dependent. Analyses of experimental data help us to understand the involved mechanisms and their interactions. On the one hand, this is useful for the numerical developments which should be carried out depending upon the configuration. On the other hand, quantitative criterion could be established to validate the simulation results. Following the above research methodology, we aim to study the disintegration of planar turbulent liquid sheets produced by a triple-disk injector. Experimental measurements provide the sheet images, used as input for a multi-scale analysis. We investigate, thanks to the latter, the behaviours of the liquid sheet, the ligaments appearing on its edges and the resulting droplets. Moreover, two immersed boundary methods are developed, aiming to simultaneously solve the nozzle flow and the breakup process. We carry out two applications, the first one on a liquid jet ejected by a cylindrical nozzle and the other a planar sheet issuing from a triple-disk injector.

Le but de cette thèse est d'étudier numériquement les écoulements diphasiques liquide-gaz à l'aide d'une méthode de suivi d'interface précise. Tout d'abord, nous mettons en place une configuration turbulence homogène isotrope diphasique. Cette configuration est utilisée pour étudier la turbulence liquide-gaz ainsi que le modèle ELSA. A l'aide de la simulation présentée il a été possible de déterminer les constantes de modélisation et de valider les termes sources utilisés dans la zone dense du spray. Ensuite, le phénomène d'évaporation est étudié en utilisant dans un premier temps un scalaire passif puis en utilisant un formalisme DNS d'évaporation. Les équations d'énergie et des espèces ont été ajoutées dans le code ARCHER. La validation de la DNS d'évaporation a été réalisée en comparant nos résultats aux solutions théoriques, tel que la loi du D2. Les limitations et les apports de cette approche sont finalement discutés et des perspectives d'améliorations sont proposées. / The aim of this thesis is to study numerically two phase flow using accurate interface tracking method. First, a two phase flow homogeneous isotropic turbulence is performed. This numerical configuration is used to study two phase flows turbulence and the ELSA model used in primary atomization modelling. Based on these results, modelling constants and source terms have been determined and validated. Then the evaporation process is studied and modelized by using a passive scalar and then by using a DNS formalism. Energy and species equations are added in the ARCHER code. Validation of the DNS performed by comparing the DNS results with theorical solution, such as the D2 law. Finally, limitations and interests of this approach are discussed and further improvements are proposed.