L’atomisation assistée d’une phase liquide lente par un co-courant gazeux rapide est un sujet largement étudié dans la littérature, et des avancées notables sont intervenues notamment sur les mécanismes de brisure, la structure du jet atomisé ainsi que sur les caractéristiques des gouttes formées. En revanche, peu d’études traitent d’une configuration où la phase lente consiste en un jet diphasique gaz-liquide. Cette situation se rencontre par exemple lors du transitoire d’allumage des moteurs cryotechniques de fusée durant lequel la fraction volumique de gaz passe continument de 1 (jet interne purement gazeux) à 0 (jet interne purement liquide), de sorte que pratiquement tous les régimes d’écoulements diphasiques, allant du régime à bulles jusqu’aux écoulements annulaires, peuvent être observés.L’objectif est donc de comprendre comment la fraction volumique de gaz et/ou le régime d’écoulement diphasique du jet interne impactent les modes d’atomisation et in fine les caractéristiques du spray.Pour répondre à ces questions, des expérimentations ont été menées avec comme fluides de substitution de l’air et de l’eau en conditions ambiantes et sous gravité terrestre. Les trois paramètres de contrôle principaux sont la vitesse superficielle du liquide qui a été variée de 0,17 m/s à 2 m/s, la vitesse superficielle du gaz dans le jet interne qui a été fixée de telle sorte que la fraction de débit gaz balaye la plage 0 à 0,99 et enfin la vitesse du gaz externe qui a évolué entre de 20 à 200 m/s. Trois géométries d’injecteurs axisymétriques ont été utilisées pour d’une part accéder à tous les régimes d’écoulements diphasiques souhaités excepté l’écoulement à brouillard, et d’autre part pour varier le diamètre du jet central d’un facteur d’environ deux. Deux types de campagnes expérimentales ont été réalisées : une campagne à rapport des pressions dynamiques gaz-liquide fixé à 16 pour des fractions de débit volumique gaz variables, ainsi que des campagnes à fractions de débit volumique gaz fixe et M variable .Les caractéristiques structurelles du spray, sa longueur de brisure et l’angle du spray formé ont été mesurés par imagerie rapide alors que les caractéristiques de la phase dispersée, c’est-à-dire tailles, vitesses et flux de gouttes ont été mesurés par sonde optique.Les cartographies des régimes d’écoulements dans l’injecteur et des structures du jet diphasique avec et sans assistance par le gaz externe que nous avons établies ont permis de démontrer que ces structures étaient étroitement liées au régime d’écoulement du jet central. Trois modes d’atomisation principaux ont été identifiés et leur frontières établies. A faible fraction de débit gaz, l’atomisation de jets liquides chargés en petites bulles est sujet à l’épluchage de surface et aux battements latéraux à grande échelle comme sur un jet monophasique liquide. A très grande fraction de débit gaz, l’écoulement annulaire donne lieu à l’atomisation d’une nappe annulaire. Pour des valeurs intermédiaires, de nouvelles structures de type "parapluie" se forment à l’arrivée des bouchons de gaz caractérisées par une grande amplitude et un développement orthogonal au jet. L’atomisation des écoulements à régimes « churn » et annulaire donne lieu à des sprays à caractère intermittent du fait de passage de blocs liquides issus de l’écoulement interne.La longueur de brisure est réduite par l’ajout de gaz interne jusqu’à devenir très petite pour les fractions de débit gaz élevées. Le comportement de l’angle du spray est différent selon le diamètre du jet atomisé et le régime d’écoulement interne : il peut augmenter ou réduire selon la configuration.Les pdf centrées sur la taille goutte moyenne sont peu sensibles à la fraction de débit gaz. En revanche les tailles de gouttes moyennes et le flux volumique montrent des évolutions marquées : ils peuvent selon la fraction de débit gaz et donc selon la structure du jet atomisé réduire ou augmenter. / Assisted atomization of a liquid phase slow by a rapid gas co-current is a topic widely studied in the literature, and significant advances have occurred especially on the breakup mechanisms, the structure of the atomized jet as well as the characteristics of formed drops. However, few studies deal with a configuration where the slow phase consists of a two-phase liquid-gas jet. This situation occurs for example during the transitional ignition of cryogenic rocket engines during which the volumic gas fraction decreases continuously from 1 (purely gas) to 0 (purely liquid), so that almost all two-phases flow regimes, from bubbly flow to annular flow can be observed.The goal is to understand how the volumic gas fraction and/or two-phase flow regime of internal jet impact the atomization modes and the characteristics of the spray.To answer these questions, experiments were conducted with as fluid of substitution air and water under ambient conditions and under gravity. The three main control parameters are the superficial velocity of the liquid which was varied from 0.17 m/s to 2 m/s, the superficial gas velocity in the internal jet that has been set so that the gas flow rate fraction sweeps the range 0 to 0.99 and finally the external gas velocity that has evolved between 20 to 200 m/s. Three geometries of axisymmetric injectors were used to firstly access any desired phase flow regimes except mist flow, and also to vary the diameter of the central jet by a factor of about two. Two types of experimental campaigns were carried out: a campaign where the gas-liquid dynamic pressure ratio was set at 16 for varied gas flow rate fraction, as well as campaigns with fixed gas flow rate fraction and variable M.The structural characteristics of the spray, its breakup length and the angle of spray were measured by high speed imaging while the characteristics of the dispersed phase, that is to say, sizes, velocities and flows of the drops were measured by optical probe.Mapping of flow regimes in the injector and two-phase jet structures with and without assistance by external gas that we have established have shown that these structures were closely related to the flow regime of the central jet. Three main atomization modes were identified and its borders established. For small gas flow rate fraction, the atomization of liquid jets laden bubbles is subject to surface peeling and large-scale lateral beats like a single phase liquid jet. For very large gas flow rate fraction, the annular flow results in the atomization of an annular liquid sheet. For intermediate values, new structures type of umbrella form at the arrival of gas slugs characterized by high amplitude and orthogonal development with respect to the jet. Atomization of “churn" flow and annular flow gives rise to intermittent sprays because of passage of "liquid blocks" from the internal flow.The breakup length is reduced by the addition of internal gas and become very small for the high gas flow rate fractions. The behavior of the angle of the spray is different depending on the diameter of the atomized jet and the internal flow regime. It may therefore increase or decrease depending on configuration.Centred pdf on mean drop size are not much sensitive to the gas flow rate fraction. However mean drop sizes and volumic fluxes show marked evolution: they can according to the gas flow rate fraction and therefore the atomized jet structure decrease or increase.

Ce travail de thèse s’intéresse aux phénomènes de surface ayant lieu lorsque l’on combine un procédé en phase homogène – contrôlé par la chimie d’un plasma non-thermique – et un procédé en phase hétérogène – contrôlé par la chimie ayant lieu à la surface d’un matériau nanostructuré Ag/TiO₂/SiO₂ – lors de la dégradation de l’acétaldéhyde, CH₃CHO.Il a été montré que le procédé diphasique permet de convertir 100 % de l’acétaldéhyde à traiter avec une SIE de 168 J.L-1 (soit une puissance de 280 mW). Dans ces conditions, CH₃CHO est converti en COx à plus de 60 %. Une telle efficacité n’est pas atteinte avec les procédés en phase homogène et en phase hétérogène seuls. Les processus se déroulant au sein du procédé diphasique mènent donc à une dégradation de CH₃CHO autrement meilleure que l’ensemble des cinétiques mises en oeuvre lors de l’utilisation des deux procédés seuls.Afin de comprendre quels processus physico-chimiques permettent d’obtenir un tel effet de synergie, l’étude de l’interaction acétaldéhyde/surface a été initiée, par spectroscopie infrarouge à réflexion diffuse (DRIFTS), et constitue le coeur de ce travail de thèse. Une attention particulière a été portée à l’étude des modes d’adsorption de l’acétaldéhyde sur Ag/TiO₂/SiO₂ en absence de plasma. Puis, l’effet de l’apport d’une source thermique et d’une espèce à fort pouvoir oxydant (l’ozone) sur l’acétaldéhyde présent en phase adsorbé a été évalué. / This thesis investigates the surface phenomena which occur when combining a homogeneous phase process – governed by the chemistry of a non-thermal plasma – and a heterogeneous phase process – controlled by the chemistry taking place on the surface of a nanostructured Ag/TiO₂/SiO₂ material – during acetaldehyde (CH₃CHO) removal.It has been shown that acetaldehyde can be removed up to 100 % with a 168 J.L-1 SIE consumption, by using the diphasic process. In these conditions, CH₃CHO is converted into 60 % of COx. Such efficiency is not achieved when using the homogeneous and heterogeneous phase processes alone. Thus, the physico-chemical phenomena occurring in the diphasic process allow a higher CH₃CHO removal compared to the whole kinetics involved in the homogeneous and heterogeneous phase processes alone. So as to understand which physico-chemical processes are involved in this synergistic effect, the study of the acetaldehyde/surface interaction has been started, by Diffuse-Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), in this thesis. The acetaldehyde adsorption modes on the Ag/TiO₂/SiO₂ surface, without plasma, have been pointed out. Moreover, the effect of bringing a thermal energy source or an oxidizing species (like ozone) on adsorbed acetaldehyde has been evaluated.

Os controladores eletrônicos de pulverização visam minimizar a variação das taxas de insumos aplicadas no campo. Eles fazem parte de um sistema de controle, e permitem a compensação da variação de velocidade de deslocamento do pulverizador durante a operação. Há vários tipos de controladores eletrônicos de pulverização disponíveis no mercado e uma das formas de selecionar qual o mais eficiente nas mesmas condições, ou seja, em um mesmo sistema de controle, é quantificar o tempo de resposta do sistema para cada controlador específico. O objetivo desse trabalho foi estimar os tempos de resposta para mudanças de velocidade de um sistema eletrônico de pulverização via modelos de regressão não lineares, estes, resultantes da soma de regressões lineares ponderadas por funções distribuição acumulada. Os dados foram obtidos no Laboratório de Tecnologia de Aplicação, localizado no Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura \"Luiz de Queiroz\", Universidade de São Paulo, no município de Piracicaba, São Paulo, Brasil. Os modelos utilizados foram o logístico e de Gompertz, que resultam de uma soma ponderada de duas regressões lineares constantes com peso dado pela função distribuição acumulada logística e Gumbell, respectivamente. Reparametrizações foram propostas para inclusão do tempo de resposta do sistema de controle nos modelos, com o objetivo de melhorar a interpretação e inferência estatística dos mesmos. Foi proposto também um modelo de regressão não linear difásico que resulta da soma ponderada de regressões lineares constantes com peso dado pela função distribuição acumulada Cauchy seno hiperbólico exponencial. Um estudo de simulação foi feito, utilizando a metodologia de Monte Carlo, para avaliar as estimativas de máxima verossimilhança dos parâmetros do modelo. / The electronic controllers spray aimed at minimizing the variation of inputs rates applied in the field. They are part of a control system, and allow for compensation for variation spray travel speed during operation. There are several types of electronic spray controllers on the market and one way to select which more efficient under the same conditions, ie in the same system of control, is to quantify the system response time for each specific driver. The objective of this study was to estimate the response times for changes in speed of an electronic spraying system via nonlinear regression models, these resulting from the sum of weighted linear regressions for cumulative distribution functions. Data were obtained on the Application Technology Laboratory, located in the Department of Biosystems Engineering from College of Agriculture \"Luiz de Queiroz\", University of Sao Paulo, in Piracicaba, Sao Paulo, Brazil. The models used were the logistic and Gompertz, resulting from a weighted sum of two constant linear regressions with weight given by the cumulative distribution function logistics and Gumbell respectively. Reparametrization been proposed for inclusion in the control system response time models, in order to improve the statistical interpretation and inference of the same. It has also been proposed a non-linear regression model two-phase which is the weighted sum of constant linear regressions weight given by a cumulative distribution function exponential hyperbolic sine Cauchy in which a simulation study was conducted using the methodology of Monte Carlo to evaluating the maximum likelihood estimates of the model parameters.

Os controladores eletrônicos de pulverização visam minimizar a variação das taxas de insumos aplicadas no campo. Eles fazem parte de um sistema de controle, e permitem a compensação da variação de velocidade de deslocamento do pulverizador durante a operação. Há vários tipos de controladores eletrônicos de pulverização disponíveis no mercado e uma das formas de selecionar qual o mais eficiente nas mesmas condições, ou seja, em um mesmo sistema de controle, é quantificar o tempo de resposta do sistema para cada controlador específico. O objetivo desse trabalho foi estimar os tempos de resposta para mudanças de velocidade de um sistema eletrônico de pulverização via modelos de regressão não lineares, estes, resultantes da soma de regressões lineares ponderadas por funções distribuição acumulada. Os dados foram obtidos no Laboratório de Tecnologia de Aplicação, localizado no Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura \"Luiz de Queiroz\", Universidade de São Paulo, no município de Piracicaba, São Paulo, Brasil. Os modelos utilizados foram o logístico e de Gompertz, que resultam de uma soma ponderada de duas regressões lineares constantes com peso dado pela função distribuição acumulada logística e Gumbell, respectivamente. Reparametrizações foram propostas para inclusão do tempo de resposta do sistema de controle nos modelos, com o objetivo de melhorar a interpretação e inferência estatística dos mesmos. Foi proposto também um modelo de regressão não linear difásico que resulta da soma ponderada de regressões lineares constantes com peso dado pela função distribuição acumulada Cauchy seno hiperbólico exponencial. Um estudo de simulação foi feito, utilizando a metodologia de Monte Carlo, para avaliar as estimativas de máxima verossimilhança dos parâmetros do modelo. / The electronic controllers spray aimed at minimizing the variation of inputs rates applied in the field. They are part of a control system, and allow for compensation for variation spray travel speed during operation. There are several types of electronic spray controllers on the market and one way to select which more efficient under the same conditions, ie in the same system of control, is to quantify the system response time for each specific driver. The objective of this study was to estimate the response times for changes in speed of an electronic spraying system via nonlinear regression models, these resulting from the sum of weighted linear regressions for cumulative distribution functions. Data were obtained on the Application Technology Laboratory, located in the Department of Biosystems Engineering from College of Agriculture \"Luiz de Queiroz\", University of Sao Paulo, in Piracicaba, Sao Paulo, Brazil. The models used were the logistic and Gompertz, resulting from a weighted sum of two constant linear regressions with weight given by the cumulative distribution function logistics and Gumbell respectively. Reparametrization been proposed for inclusion in the control system response time models, in order to improve the statistical interpretation and inference of the same. It has also been proposed a non-linear regression model two-phase which is the weighted sum of constant linear regressions weight given by a cumulative distribution function exponential hyperbolic sine Cauchy in which a simulation study was conducted using the methodology of Monte Carlo to evaluating the maximum likelihood estimates of the model parameters.

Lors de la phase de rentrée atmosphérique d'une sonde spatiale, la paroi du corps est le siège de phénomènes physico-chimiques complexes. Nous nous intéressons dans cette thèse au cas où le matériau solide de l'objet de vol comporte plusieurs constituants s'ablatant de façon différentielle. En particulier, l'un de ces constituants subit un changement de phase donnant lieu à l'apparition d'une phase liquide. Nous sommes en présence de trois phases : solide, liquide et gaz. Les travaux effectués dans cette thèse correspondent au développement de méthodes numériques en 2D capables de modéliser les différentes interfaces en présence ainsi que l'évolution des fluides ou des matériaux séparés par celle-ci. L'enjeu principal de la thèse est de proposer des méthodes et des algorithmes de couplage pour l'écoulement diphasique, la thermique multimatériaux et les changements de phase (fusion et sublimation) / During atmospheric reentry phase of a spacecraft, its body surface is the seat of complex physico-chemical phenomena. We focus in this thesis on the case where the wall of the flying object has several components ablating differentially. In particular, one of those components undergoes a phase change giving the rise to the introduction of a liquid phase. We have three phases in the domain: solid, liquid and gas phases.The work done in this thesis corresponds to the development of 2D numerical methods which can modelize the different interfaces. The main issue of this thesis is to propose methods and algorithms for coupling the two-phase flow, multi-material heat problems and phase changes (melting and sublimation).