Acoustic levitation is a method which uses sound radiation to suspend matter in a medium. The main use of this phenomenon is for the contactless processing of matter, allowing to manipulate small objects without any solid contact. Contactless processing of matter presents many advantages in, for example, the fabrication of MEMS (microelectromechanical systems) where handling the components is challenging because of their fragile and surface-sensitive characteristics or in the chemical/biological industry when handling high-purity or hazardous materials. Thus, a new device for noncontact linear transportation of small solid objects is presented here. In this device, ultrasonic flexural vibrations are generated along the ring shaped vibrator using two Langevin transducers and by using a reflector parallel to the vibrator, small particles are trapped at the nodal points of the resulting acoustic standing wave. The particles are then moved by generating a traveling wave along the vibrator, which can be done by modulating the vibration amplitude of the transducers. The working principle of the traveling wave along the vibrator has been modeled by the superposition of two orthogonal standing waves, and the position of the particles can be predicted by using finite element analysis of the vibrator and the resulting acoustic field. A prototype consisting of a 3 mm thick, 220 mm long, 50 mm wide and 52 mm radius aluminum ring-type vibrator and a reflector of the same length and width was built and small polystyrene spheres have been successfully transported along the straight parts of the vibrator. / Levitação acústica é um método para suspender matéria em um meio através de pressão de radiação acústica gerada por intensas ondas de som. O principal uso desse fenômeno é na manipulação de partículas sem contato solido. Esse fenômeno tem várias aplicações para pesquisas onde deve ser evitado todo o contato como, por exemplo, na área de biologia, química, e na fabricação de MEMS. Assim, um novo sistema de transporte linear de partículas por levitação acústica está apresentado aqui. Nesse sistema, vibrações flexurais estão geradas em uma placa tipo anel com dois transdutores tipo Langevin, e colocando um refletor paralelo ao oscilador, partículas estão presas no pontos nodais da onda acústica gerada. As partículas estão deslocadas modulando a amplitude dos transdutores. Assim, este trabalho tem como objetivos a modelagem do fenômeno de levitação acústica, o dimensionamento de um protótipo de sistema de transporte linear de partículas por levitação acústica, bem como a fabricação e o controle desse protótipo. Um protótipo consistindo de uma estrutura tipo anel de alumínio de 3 mm de espessura, 220 mm de comprimento e um raio de 52 mm foi fabricado e o transporte de pequenas esferas de isopor foi realizado com êxito nas parte retas do vibrador.

Acoustic levitation is a method which uses sound radiation to suspend matter in a medium. The main use of this phenomenon is for the contactless processing of matter, allowing to manipulate small objects without any solid contact. Contactless processing of matter presents many advantages in, for example, the fabrication of MEMS (microelectromechanical systems) where handling the components is challenging because of their fragile and surface-sensitive characteristics or in the chemical/biological industry when handling high-purity or hazardous materials. Thus, a new device for noncontact linear transportation of small solid objects is presented here. In this device, ultrasonic flexural vibrations are generated along the ring shaped vibrator using two Langevin transducers and by using a reflector parallel to the vibrator, small particles are trapped at the nodal points of the resulting acoustic standing wave. The particles are then moved by generating a traveling wave along the vibrator, which can be done by modulating the vibration amplitude of the transducers. The working principle of the traveling wave along the vibrator has been modeled by the superposition of two orthogonal standing waves, and the position of the particles can be predicted by using finite element analysis of the vibrator and the resulting acoustic field. A prototype consisting of a 3 mm thick, 220 mm long, 50 mm wide and 52 mm radius aluminum ring-type vibrator and a reflector of the same length and width was built and small polystyrene spheres have been successfully transported along the straight parts of the vibrator. / Levitação acústica é um método para suspender matéria em um meio através de pressão de radiação acústica gerada por intensas ondas de som. O principal uso desse fenômeno é na manipulação de partículas sem contato solido. Esse fenômeno tem várias aplicações para pesquisas onde deve ser evitado todo o contato como, por exemplo, na área de biologia, química, e na fabricação de MEMS. Assim, um novo sistema de transporte linear de partículas por levitação acústica está apresentado aqui. Nesse sistema, vibrações flexurais estão geradas em uma placa tipo anel com dois transdutores tipo Langevin, e colocando um refletor paralelo ao oscilador, partículas estão presas no pontos nodais da onda acústica gerada. As partículas estão deslocadas modulando a amplitude dos transdutores. Assim, este trabalho tem como objetivos a modelagem do fenômeno de levitação acústica, o dimensionamento de um protótipo de sistema de transporte linear de partículas por levitação acústica, bem como a fabricação e o controle desse protótipo. Um protótipo consistindo de uma estrutura tipo anel de alumínio de 3 mm de espessura, 220 mm de comprimento e um raio de 52 mm foi fabricado e o transporte de pequenas esferas de isopor foi realizado com êxito nas parte retas do vibrador.

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Evaporation of pure and binary liquid droplets is of interest in thermal sprays and spray drying of food, ceramics and pharmaceutical products. Understanding the rate of heat and mass transfer in any drying process is important not only to enhance evaporation rate or vapor-gas mixing, but also to predict and control the final morphology and microstructure of the precipitates. Acoustic levitation is an alternative method to study micron-sized droplets without wall effects, which eliminates chemical and thermal contamination with surfaces. This work uses an ultrasonic levitation technique to investigate the vaporization dynamics under radiative heating, with focus on evaporation characteristics, precipitation kinetics, particle agglomeration, structure formation and droplet stability. Timescale and temperature scales are developed to compare convective heating in actual sprays and radiative heating in the current experiments. These relationships show that simple experiments can be conducted in a levitator to extrapolate information in realistic convective environments in spray drying. The effect of acoustic streaming, droplet size and liquid properties on internal flow is important to understand as the heat and mass transfer and particle motion within the droplet is significantly controlled by internal motion. Therefore, the droplet internal flow is characterized by Particle Image Velocimetry for different dropsize and viscosity. Nanosuspension droplets suspended under levitation show preferential accumulation and agglomeration kinetics. Under certain conditions, they form bowl shaped structures upon complete evaporation. At higher concentrations, this initial bowl shaped structure morphs into a ring structure. Nanoparticle iv migration due to internal recirculation forms a density stratification, the location of which depends on initial particle concentration. The time scale of density stratification is similar to that of perikinetic-driven agglomeration of particle flocculation. The density stratification ultimately leads to force imbalance leading to a unique bowl-shaped structure. Chemically active precursor droplet under acoustic levitation shows events such as vaporization, precipitation and chemical reaction leading to nanoceria formation with a porous morphology. The cerium nitrate droplet undergoes phase and shape changes throughout the vaporization process followed by formation of precipitate. Ex-situ analyses using TEM and SEM reveal highly porous morphology with trapped gas pockets and nanoceria crystalline structures at 70oC. Inhomogeneity in acoustic pressure around the heated droplet can induce thermal instability. Short wavelength (Kelvin-Helmholtz) instability for diesel and bio-diesel droplets triggers this secondary atomization, which occurs due to relative velocity between liquid and gas phase at the droplet equator. On the other hand, liquids such as Kerosene and FC43 show uncontrollable stretching followed by a catastrophic break-up due to reduction in surface tension and viscosity coupled with inhomogeneity of pressure around the droplet. Finally, a scaling analysis has been established between vaporizing droplets in a convective and radiative environment. The transient temperature normalized by the respective scales exhibits a unified profile for both modes of heating. The analysis allows for the prediction of required laser flux in the levitator experiments to show its equivalence in a corresponding heated gas stream. The theoretical equivalence shows good agreement with experiments for a range of droplet sizes.

O objetivo deste trabalho é estudar o fenômeno da força de radiação acústica produzida por ondas progressivas e estacionárias. Neste trabalho o estudo da força produzida por ondas estacionárias é aplicado na análise de um levitador acústico e o estudo da força de radiação acústica por ondas progressivas é feito visando a futura construção de um separador acústico. Neste trabalho é utilizado o método dos elementos finitos para simular o comportamento de um levitador acústico. Primeiramente, é feita a simulação de um levitador acústico que consiste de um transdutor de Langevin com uma face de emissão plana que opera na freqüência de aproximadamente 20 kHz e um refletor plano. O método dos elementos finitos é utilizado para determinar o deslocamento da face do transdutor e o potencial acústico que atua numa esfera pequena. O deslocamento da face do transdutor obtido numericamente é comparado com o medido experimentalmente por um vibrômetro de fibra ótica e o potencial acústico determinado pelo método dos elementos é verificado experimentalmente colocando pequenas esferas de isopor no levitador. Depois de verificar o modelo numérico, o método dos elementos finitos é utilizado na otimização de um levitador acústico composto de um refletor côncavo e um transdutor com face de emissão côncava. Os resultados numéricos mostram que a força de radiação acústica no novo levitador é aumentada em 604 vezes quando comparada com o levitador composto de um transdutor com face plana e refletor plano. Este trabalho também apresenta um modelo numérico para determinar a trajetória de partículas esféricas na presença de uma onda de ultra-som progressiva. O modelo assume que as seguintes forças atuam na partícula: gravidade, empuxo, forças viscosas e força de radiação acústica devido a uma onda progressiva. Com o objetivo de não restringir o tamanho das partículas que podem ser utilizadas no modelo é empregada uma equação empírica do coeficiente de arrasto, válida para uma grande faixa de número de Reynolds. O modelo proposto requer a distribuição de pressão gerada pelo transdutor de ultra-som. A distribuição de pressão é medida experimentalmente utilizando um hidrofone calibrado. A verificação do modelo é feita soltando-se pequenas esferas de vidro (com diâmetros da ordem de 500 m) em frente a um transdutor de ultra-som de 1 MHz e 35 mm de diâmetro. / The objective of this work is to study the acoustic radiation force produced by progressive and standing waves. In this work, the studies related to the acoustic radiation force generated by ultrasonic standing waves are applied in the analysis of an acoustic levitator and the studies involving the acoustic radiation force generated by progressive waves are conducted aiming the design of acoustic separators. In this work, the finite element method is used to simulate an acoustic levitator. First, an acoustic levitator consisting of a 20 kHz Langevin ultrasonic transducer with a plane radiating surface and a plane reflector is simulated by the finite element method. The finite element method is used to determine the transducer face displacement and the acoustic radiation potential that acts on a small sphere. The numerical displacement is compared with that obtained by a fiber-optic vibration sensor and the acoustic radiation potential determined by the finite element method is verified experimentally by placing small Styrofoam spheres in the levitator. After verifying the numerical method, the finite element method was used to optimize an acoustic levitator consisting of a concave-faced transducer and a curved reflector. The numerical results show that the acoustic radiation force in the new levitator is enhanced 604 times compared with the levitator consisting of a plane transducer and a plane reflector. This work also presents a numerical model to determine the trajectory of sphere particles when submitted to ultrasonic progressive waves. This model assumes that the following forces act on the particle: gravity, buoyancy, viscous forces and acoustic radiation force due to the progressive wave. In order not to restrict the model to a small particle size range, the viscous forces that act on the sphere are modeled by an empirical relationship of drag coefficient that is valid for a wide range of Reynolds numbers. The numerical model requires the pressure field radiated by the ultrasonic transducer. The pressure field is obtained experimentally by using a calibrated needle hydrophone. The numerical model validation is done by dropping small glass spheres (on the order of 500 m diameter) in front of a 1-MHz 35-mm diameter ultrasonic transducer.

O objetivo deste trabalho é estudar o fenômeno da força de radiação acústica produzida por ondas progressivas e estacionárias. Neste trabalho o estudo da força produzida por ondas estacionárias é aplicado na análise de um levitador acústico e o estudo da força de radiação acústica por ondas progressivas é feito visando a futura construção de um separador acústico. Neste trabalho é utilizado o método dos elementos finitos para simular o comportamento de um levitador acústico. Primeiramente, é feita a simulação de um levitador acústico que consiste de um transdutor de Langevin com uma face de emissão plana que opera na freqüência de aproximadamente 20 kHz e um refletor plano. O método dos elementos finitos é utilizado para determinar o deslocamento da face do transdutor e o potencial acústico que atua numa esfera pequena. O deslocamento da face do transdutor obtido numericamente é comparado com o medido experimentalmente por um vibrômetro de fibra ótica e o potencial acústico determinado pelo método dos elementos é verificado experimentalmente colocando pequenas esferas de isopor no levitador. Depois de verificar o modelo numérico, o método dos elementos finitos é utilizado na otimização de um levitador acústico composto de um refletor côncavo e um transdutor com face de emissão côncava. Os resultados numéricos mostram que a força de radiação acústica no novo levitador é aumentada em 604 vezes quando comparada com o levitador composto de um transdutor com face plana e refletor plano. Este trabalho também apresenta um modelo numérico para determinar a trajetória de partículas esféricas na presença de uma onda de ultra-som progressiva. O modelo assume que as seguintes forças atuam na partícula: gravidade, empuxo, forças viscosas e força de radiação acústica devido a uma onda progressiva. Com o objetivo de não restringir o tamanho das partículas que podem ser utilizadas no modelo é empregada uma equação empírica do coeficiente de arrasto, válida para uma grande faixa de número de Reynolds. O modelo proposto requer a distribuição de pressão gerada pelo transdutor de ultra-som. A distribuição de pressão é medida experimentalmente utilizando um hidrofone calibrado. A verificação do modelo é feita soltando-se pequenas esferas de vidro (com diâmetros da ordem de 500 m) em frente a um transdutor de ultra-som de 1 MHz e 35 mm de diâmetro. / The objective of this work is to study the acoustic radiation force produced by progressive and standing waves. In this work, the studies related to the acoustic radiation force generated by ultrasonic standing waves are applied in the analysis of an acoustic levitator and the studies involving the acoustic radiation force generated by progressive waves are conducted aiming the design of acoustic separators. In this work, the finite element method is used to simulate an acoustic levitator. First, an acoustic levitator consisting of a 20 kHz Langevin ultrasonic transducer with a plane radiating surface and a plane reflector is simulated by the finite element method. The finite element method is used to determine the transducer face displacement and the acoustic radiation potential that acts on a small sphere. The numerical displacement is compared with that obtained by a fiber-optic vibration sensor and the acoustic radiation potential determined by the finite element method is verified experimentally by placing small Styrofoam spheres in the levitator. After verifying the numerical method, the finite element method was used to optimize an acoustic levitator consisting of a concave-faced transducer and a curved reflector. The numerical results show that the acoustic radiation force in the new levitator is enhanced 604 times compared with the levitator consisting of a plane transducer and a plane reflector. This work also presents a numerical model to determine the trajectory of sphere particles when submitted to ultrasonic progressive waves. This model assumes that the following forces act on the particle: gravity, buoyancy, viscous forces and acoustic radiation force due to the progressive wave. In order not to restrict the model to a small particle size range, the viscous forces that act on the sphere are modeled by an empirical relationship of drag coefficient that is valid for a wide range of Reynolds numbers. The numerical model requires the pressure field radiated by the ultrasonic transducer. The pressure field is obtained experimentally by using a calibrated needle hydrophone. The numerical model validation is done by dropping small glass spheres (on the order of 500 m diameter) in front of a 1-MHz 35-mm diameter ultrasonic transducer.

Als Totalanalysesysteme (TAS) werden Geräte bezeichnet, welche komplette chemische Analysen eigenständig ausführen. Die Einführung solcher Systeme ermöglicht einen effizienteren Arbeitsablauf in Analyselaboren, da beispielsweise die Probenmanipulation, Aufreinigung und die physikalisch-/chemische Analyse automatisiert in einem Arbeitsgang durchgeführt werden können. Die speziellen Mikrototalanalysesysteme benötigen geringere Probemengen im $\mu$L- Bereich. Durch Kontamination, Agglomeration oder einem Verschluss etwaiger Kanäle in mikrofluidischen Totalanalysesystemen kann es zu einem kompletten Systemausfall kommen. Eine Alternative bildet die akustische Levitation, um derartige Störfälle durch gänzlichen Verzicht auf Gefäße und Wandkontakte gezielt zu reduzieren. Damit die akustische Levitation erfolgreich in Mikrototalanalysesystemen Anwendung finden kann, bedarf es der technischen Weiterentwicklung von Analysemethoden und Kopplungstechniken. In der vorliegenden Arbeit wird das Hauptaugenmerk auf die Kopplung von Levitationstechnik und Massenspektrometrie gelegt. Darüber hinaus wurden spektroskopische Experimente durchgeführt, welche auf Totalreflektionen innerhalb der Tropfen beruhen. Die besonders gute Reflektion hängt damit zusammen, dass sich die Phasengrenze zwischen Luft und Flüssigkeit im Schwebezustand durch molekulare Wechselwirkungen ständig erneuert und keine produktionsbedingte raue Oberfläche aufweist. Die Kombination aus automatischer Tropfengenerierung, Spektroskopie sowie der entwickelten Methode zur Ionenerzeugung aus dem Probevolumen und der massenspektrometrischen Analyse bilden die Grundlage eines neuartigen Mikrototalanalysesystems für geringe Probemengen. / As a total analysis system (TAS) an instrument is called which carries out complete chemical analysis procedures independently. The introduction of such systems offers a more efficient workflow in analytical laboratories because the sample manipulation, purification and the actual automated analysis can be carried out in one single operation. Specialized and already existing micro total analysis systems require currently a small amount of sample in the $\mu$L range. Owing to contamination, agglomeration and thus cross-secion reduction of incorporated channels in micro fluidics total analysis systems it can lead to a complete system interruption. Hence, the implementation of acoustic levitation in these systems is interessting alternative in order to avoid such kind of problems by abandoning vessels and wall contacts completely. To ensure acoustic levitation in micro total analysis systems can be successfully applied, technical development of analytical methods and coupling techniques is required. In the present work, the coupling of levitation technology and mass spectrometry is the prioritized topic but, in addition, spectroscopic experiments based on total reflections within the levitated droplet are as well realized in order to gain process insights. The particularly good reflection at the freely levitated droplet's circumference is due to the fact that the phase boundary between air and liquid is renewed by molecular interactions constantly and has no production-related rough surface. The combination of automated droplet generation, spectroscopy as well as the developed method for ion generation from the sample volume and mass spectrometry forms the basis of a novel micro total analysis system for small sample quantities.

Orientador: Átila Madureira Bueno / Resumo: O som é uma onda mecânica e como tal transporta energia que age sobre partículas devido às forças de radiação acústica. O princípio para suspender corpos é aplicar uma força de tal forma a equilibrar seu peso. Na técnica de levitação acústica (AcLev) uma pequena esfera pode ser suspensa pela força de radiação acústica gerada por uma onda estacionária, sendo que o ponto de levitação está localizado na região em que o potencial acústico é mínimo, que é condição necessária para levitar uma esfera com raio muito menor que o comprimento de onda. Levitação acústica (AcLev) é uma ferramenta importante para manusear objetos sem contêineres. Nos anos recentes muitos dispositivos foram desenvolvidos com sucesso devido ao comportamento estável dos dispositivos AcLev. Como resultado, a maioria dos trabalhos sobre Aclev se concentram sobre simulações numéricas ou testes experimentais para estudar a geometria e arranjos dos emissores acústicos, ou a influência de vários tipos de perturbações, e a maioria desses modelos matemáticos considera somente o potencial acústico. Neste trabalho, a equação não linear de movimento para uma partícula levitada imersa em campo acústico de eixo único foi desenvolvida, considerando também forças dissipativas. O espaço parâmetro foi examinado buscando a existência de bifurcações, e faixas de projeto para os ganhos do dispositivo AcLev foram determinadas a partir da condição de existência de pontos de equilíbrio. Em adição, o comportamento dinâmico do dispos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Sound is a mechanical wave and aims to carry energy that acts on particles due to acoustic radiation forces, while the principle to suspend bodies is to apply a force in such a way as to balance their weight. In the acoustic levitation technique (Aclev) a small sphere can be suspended by the acoustic radiation force generated by a stationary wave and the levitation point is located in the region where the acoustic potential is minimal, which is a necessary condition for levitating a sphere with radius much smaller than the wavelength. AcLev is an important tool for handling objects without the use of containers. In recent years many devices have been successfully developed due to the stable behavior of AcLev. As a result, most works on Aclev focuses on numerical simulations and experimental tests to study the geometry and arrangement of acoustic emitters, or the influence of various kinds of perturbations, and most mathematical models consider only acoustic potential. In this work, the nonlinear equation of motion for a levitated particle immersed in an acoustic field with single axis was developed considering also dissipative forces. The parameter space was searched for the existence of bifurcations and the design range for AcLev device gains were determined from the condition of equilibrium points. In addition, the dynamic behavior of the AcLev device regarding gains has been studied, also considering the microgravity situation. Numerical simulations corroborated the analyt... (Complete abstract click electronic access below) / Mestre

Ultraschalllevitation kombiniert die Vorteile von Mikrofluidik, wie beispielsweise die sehr geringe benötigte Probenmenge, mit einer wandlosen Probenhandhabung. Obwohl die Kopplung zwischen le- vitierten Tröpchen und verschiedenster analytischer Methoden wie optischer Spektroskopie und Röntgenbeugung sehr genau untersucht ist, fehlt es immer noch an einer etablierten Kopplung mit einer massenspektrometrischen Methode für die Analyse auf molekularer Ebene. Die vorliegende Arbeit beschreibt die Prinzipien, auf denen eine kontaktlose massenspektrometrische Analyse von levitierten flüssi- gen Proben beruht. Zuerst wurde der neu entworfene akustische Levitator bezüglich des Einflusses seiner Geometrie auf die Levi- tationseigenschaften experimentell und mittels numerischer Simul- tationen untersucht. Die anschließend durch geführten Experimen- te demonstrieren das Potential von Infrarot-Lasern als kombinierte Desorptions- und Ionisationsquelle für organische Substanzen aus einer Mischung aus Wasser und Glycerin als Cromophor. Um einen tieferen Einblick in die hierbei ablaufenden Ionisationsmechanismen zu erhalten, wurde als Modell ein “Sonic-Spray” Konus räumlich per Massenspektrometrie und Laser-induzierter Fluoreszenz untersucht. Levitator-Geometrie auf die Levitationseigenschaften stimmen sehr gut mit numerischen Simulationen überein. Als komplementäre Ionisationsmethode wurde eine Niedertemperatur-Plasmaquelle ein- gesetzt. Nach einer zeitaufgelösten Untersuchung der grundlegenden Ionisationsmechanismen wurde diese Quelle für die Untersuchung flüchtiger Spezies aus der levitierten Probe in deren direkten Umgebung ohne störende Interferenzen ge- nutzt. / Ultrasonic levitation combines advantages of microfluidics like the required small sample volumes with a wall-less sample handling. While the coupling of analytical methods like optical spectroscopy as well as x-ray scattering are very well elaborated, an established mass spectrometric method to obtain molecular analytical information is still lacking. The herein presented work describes the fundamental processes for a contactless mass spectrometric analysis of levitated droplets. First, the influences of the specially designed levitator geometry on the levitation capabilities is described. During further experiments, the use of infrared lasers has proven useful as a combined desorption and ionization source for organic molecules from a mixture of water and glycerol as chromophore. Subsequently, sonic-spray ionization was used to gain a deeper understanding of the ionization processes occurring within the spray plume. Mass spectrometric mapping as well as laser-induced fluorescence were performed to investigate the ionization during an aerodynamic breakup of the micro droplets in the spray process. As a complementary sampling method, the ionization with a low- temperature plasma source is described. First, a time-resolved mass spectrometric investigation of the ionization process is shown. Sub- sequent to this fundamental study, the application of such a plasma source for the direct analysis of volatile compounds from within the droplets in the surrounding environment without interferences from the droplets bulk phase is described.

Ces travaux s’inscrivent dans le cadre des recherches sur l’optimisation du séchage par atomisation de suspensions colloïdales employées pour la production de supports de catalyseurs. Pour mieux appréhender les phénomènes fondamentaux qui régissent ce procédé, le problème a été ramené à celui de l’étude expérimentale et la modélisation du séchage d’une goutte unique en lévitation dans un champ acoustique sous flux gazeux. L’expérience permet de contrôler les différents paramètres de séchage dans la chambre d’évaporation. Le suivi du séchage a été réalisé à l’aide de techniques optiques (vélocimétrie laser, imagerie en transmission et diffractométrie à l’angle d’arc-en-ciel) et des analyses post-mortem complémentaires. L’emploi de la diffractométrie arc-en-ciel a nécessité le développement d’un modèle d’optique géométrique avancé capable de décrire la diffusion de gouttes ellipsoïdales et les effets des suspensions nanoparticulaires sur le phénomène d’arc-en-ciel. Le modèle de séchage est un modèle à symétrie radiale. Il permet de prédire les taux d’évaporation, les profils internes de concentration et la déformation finale du grain. Les comparaisons expérimentales ont montré qu’il prédit très correctement le taux de séchage des gouttes colloïdales pour des nombres de Reynolds compris entre 100 et 230, des températures comprises entre 25°C et 55°C et des taux d’hygrométrie compris entre 2.5% et 70%. Il ressort également que le seuil de croûtage, identifié ici à partir du changement de régime du taux d’évaporation, semble intervenir pour des concentrations volumiques locales en nanoparticules de l’ordre de 12.3% bien inférieures aux concentrations de blocage des pâtes. / This PhD work takes place in the framework of researches on the optimization of the spray drying of colloidal suspensions used for catalyst support production. To better understand fundamental phenomena governing this process, the problem is reduced to the experimental study and modelling of the drying of a single droplet levitated in an acoustic field with an external gas flow. The experiment allows also controlling parameters such as composition of the suspension, temperature or humidity inside evaporation chamber. The drying is monitored using in situ optical diagnostics (particle image velocimetry, shadowgraphy and rainbow diffractometry) as well as post-mortem analyzes. The use of rainbow diffractometry has required the development of advanced light scattering models accounting for the droplet non-sphericity and heterogeneity. The drying model is a model with radial symmetry. It predicts various quantities such as the droplet evaporation rate, internal concentration profile or the deformation of the final grain. Experimental comparisons show that this model can accurately predicts the drying rate of colloidal droplet for Reynolds numbers ranging from 100 to 230, temperatures between 25°C and 55°C and relative humidity between 2.5% and 70%. It is also shown that the crust compactness factor, about 12% when identified from the change in the rate of evaporation, is much lower than that reported classically for the jamming of dense suspensions.