Pheroid is a patented system comprising of a unique submicron emulsion type formulation. Pheroid vesicles consist mainly of plant and essential fatty acids and can entrap, transport and deliver pharmacologically active compounds and other useful molecules. The aim of this study was to show that a modulation of components and parameters is necessary to obtain the optimum formula to be used in pharmaceutical preparations. Non-optimal or non-predictable stability properties of emulsions can be limiting for the applications of emulsions (Bjerregaard et al., 2001:23). Careful consideration was given to the apparatus used during the processing along with the ratios of the various components added to the formulation and the storage conditions of the Pheroid vesicles. A preliminary study was performed to optimize the most accurate processing parameters during emulsification. The effect of emulsification rate and time, the temperature of the aqueous phase, the number of days the water phase were gassed, the concentration of the surfactant, cremophor® RH 40, used and the concentration of Vitamin F Ethyl Ester CLR added to the oil phase of the o/w emulsion has been studied. Quantification of the mean particle size, zeta potential, turbidity, pH and current values were used to characterize the emulsions. The samples were characterised after 1, 2, 3, 7, 14, 21 and 28 days of storage. The emulsions were also characterised with confocal laser scanning microscopy (CLSM) to measure the number and size and size distribution of the vesicles. After determination of the processing variables influencing the emulsion stability an accelerated stability test was conducted on a final formula. In the present study, accelerated stability testing employing elevated temperatures and relative humidity were used with good accuracy to predict long-term stability of an o/w emulsion kept at both 5 and 25 OC with 60 % relative humidity and 40 OC with 75 % relative humidity. The results of the stability tests were presented in histograms of the physical properties 24 hours, 1 month, 2 months and 3 months after preparation of the emulsion. It was concluded that Pheroid vesicles demonstrate much potential as a drug delivery system. The high stability of this formula allows its use in a wide variety of applications in the pharmaceutical industry. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2007.

Le béton projeté est une méthode de mise en place consistant en la projection pneumatique de béton sur une surface à grande vitesse. Dans le cas de la méthode par voie sèche, le mélange granulats-ciment est introduit sec en machine, l'eau est ajoutée à la fin du transfert. Cette technique, très employée, est néanmoins génératrice de pertes importantes par rebond, pouvant s'élever jusqu'à 40% de la masse projetée. L'enjeu de la réduction des pertes est à la fois économique et environnemental. Les facteurs influents sur le rebond sont liés aux techniques de projection et à la formulation. Ce travail de thèse a pour objectif l'optimisation de la formulation du béton afin de réduire les pertes par rebond, mais également d'améliorer la durabilité. L'étude porte en particulier sur l'influence sur le rebond : du squelette granulaire, de la teneur en eau et de l'emploi d'additifs et/ou d'additions de substitution. Une approche modélisation du phénomène de rebond est également abordée. / Sprayed concrete is a concrete pneumatically projected onto a surface at high velocity. Dry-mix shotcrete is a process in which dry constituents are introduced into the machine and conveyed through a hose to the nozzle, where the water is added. This process is used in various civil engineering or construction projects; unfortunately, it can lead to high losses of concrete due to rebound (up to 40% of the total mass of material). Such losses induce overconsumption of material, which is damaging for the cost of the work and for the environment. Rebound depends on technicals parameters and mix design. The present work focuses on rebound reduction and also on durability enhancement by modification of the mix design. The influence of aggregate size distribution, water content and supplementary cimentitious material is studied. An analytical approach of rebound phenomenon is also implemented.

L’objectif de ce travail était d’étudier l’évolution de la morphologie des agrégats soumis à des conditions hydrodynamiques turbulentes. Pour cela, des expériences de floculation de particules de latex ont été réalisées dans un réacteur de Taylor-Couette en mettant en œuvre un séquençage des conditions hydrodynamiques, consistant en six étapes effectuées alternativement à faible et fort taux de cisaillement. Pour l’ensemble des expériences, un suivi en ligne de la taille des flocs a été réalisé par granulométrie laser. Par ailleurs, des paramètres caractéristiques de la forme des agrégats, ont été déterminés par analyse d’images sur des échantillons de suspension prélevés à la fin des différentes étapes du séquençage hydrodynamique. Dans le cas où le mécanisme de floculation est la neutralisation de charges (par ajout de NaCl ou de Al2(SO4)3), les résultats ont permis de confirmer la forte influence de l’hydrodynamique sur la taille des agrégats mais ont aussi révélé l’existence d’un lien entre la forme des agrégats et leur histoire. Contrairement à la taille, la morphologie des flocs, caractérisée par leur circularité ou leur convexité est peu sensible à l’hydrodynamique. L’étude des distributions surfaciques de ces paramètres de forme ainsi que la représentation des résultats expérimentaux sous forme bidimensionnelle (reliant taille et forme) ont en effet montré qu’après un certain nombre de cycles rupture-refloculation, la circularité comme la convexité évoluent vers une distribution unique, indépendante de l’hydrodynamique. Dans le cas où le mécanisme de floculation est le pontage (le polymère utilisé étant le PolyDADMAC), pour des taux de cisaillement faible, les agrégats sont plus grands, mais plus circulaires et plus résistants à la rupture que ceux créés par neutralisation de charge. Une analyse complémentaire est ensuite proposée permettant d’analyser l’effet des conditions hydrodynamiques sur la dimension fractale des flocs déduite des mesures par diffraction laser ou de l’analyse d’images. A des fins de comparaison, une nouvelle expression de la dimension fractale issue de l’analyse morphologique Df* a été introduite. Enfin, la modélisation de la floculation par résolution de l’équation de bilan de population basée sur la méthode de la quadrature des moments (QMOM) a été abordée ; les paramètres variables du modèle étant les valeurs expérimentales du taux de cisaillement moyen et la dimension fractale. Les résultats préliminaires montrent qu’il est possible de reproduire correctement l’évolution des six premiers moments de la distribution en taille des agrégats pour une phase d’agrégation du séquençage hydrodynamique. / The aim of this work was to investigate the evolution of the morphology of aggregates under turbulent hydrodynamic conditions. For this purpose, latex particles flocculation experiments were conducted in a Taylor-Couette reactor by carrying out a sequencing of the hydrodynamic conditions, consisting of six steps performed alternately at low and high shear rate. For all the experiments, an on-line monitoring of the size of the flocs was carried out by laser diffraction. Moreover, characteristic parameters of the shape of the aggregates were determined by image analysis on suspension samples taken at the end of the various stages of the hydrodynamic sequencing. When the flocculation mechanism is the charge neutralization (by addition of NaCl or Al2(SO4)3), the results have confirmed the strong influence of hydrodynamics on aggregate size but also revealed the existence of a relationship between the shape of the aggregates and their history. Contrary to size, the morphology of the flocs, characterized either by their circularity or convexity, is not sensitive to hydrodynamics. The study of the surface distributions of these shape parameters as well as the representation of the experimental results in two-dimensional form (linking size and shape) have shown that, after a number of breakage-reflocculation cycles, both circularity and convexity evolve towards a single distribution which is independent of hydrodynamics. When the bridging flocculation is the main mechanism (the polymer used being PolyDADMAC), at low shear rates, the aggregates are larger, but more circular and more resistant to breakage than those issued from charge neutralization. A complementary analysis is then proposed to analyze the effect of hydrodynamics on the fractal dimension measured either by laser diffraction or by image analysis. In order to compare both results, a new expression of the fractal dimension derived from the morphological analysis Df * was introduced. Finally, the modeling of the flocculation by solving the population balance equation using the quadrature method of moments (QMOM) is presented; the only variable parameters being the experimental values of the average shear rate and the fractal dimension. The preliminary results show that it is possible to reproduce correctly the evolution of the first six moments of the aggregate size distribution for an aggregation phase of the hydrodynamic sequencing.

Made available in DSpace on 2014-06-11T19:33:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-01-20Bitstream added on 2014-06-13T21:06:47Z : No. of bitstreams: 1 beraldo_jmg_dr_jabo.pdf: 1719744 bytes, checksum: a27050b0770082469a896d7df06651eb (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O sistema de semeadura direta (SSD) proporciona melhores condições físicas do solo favorecendo o armazenamento de água no solo (ARM). A hipótese do trabalho foi que o Latossolo Vermelho argiloso, em sequências de culturas de verão e inverno sob SSD afeta o ARM em decorrência da modificação nos atributos físicos do solo e que o tensiômetro de punção digital (TDig) pode ser usado para medir o potencial mátrico da água no solo. Os objetivos foram avaliar o ARM e os atributos físicos do solo em sequências de culturas de verão e de inverno sob SSD e medir o potencial mátrico da água no solo por meio do tensiômetro de mercúrio e do TDig. O delineamento foi em blocos, com três repetições, no esquema em faixas. Os tratamentos foram constituídos por três sequências de culturas de verão (rotação soja/milho e monocultura de milho e soja) e sete culturas de inverno (milho, girassol, nabo forrageiro, milheto, guandu, sorgo e crotalária). Foram instalados tensiômetros nas camadas de 0,2; 0,4 e 0,6 m. Foi determinada a densidade do solo, a distribuição de poros por tamanho nas camadas de 0-0,1 e 0,1-0,2 m e a infiltração de água na superfície do solo. Os dados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey. O TDig pode ser usado para avaliar o potencial mátrico da água no solo. O ARM não diferiu entre as sequências de culturas de verão e nas culturas de inverno houve diferença, principalmente após período de menor disponibilidade hídrica. A densidade e a porosidade do solo não foram influenciadas pelas culturas de verão e inverno. O diâmetro de poros entre 0,075 - 0,05 e 0,03 - 0,0375 mm na camada de 0,0-0,1 m diferiu entre as sequências de verão. A distribuição de poros por tamanho não foi influenciada pelas sequências de culturas de inverno. A maior infiltração de água no solo ocorreu na parcela sob monocultura de soja / No tillage system provides soil physical properties improvements, and soil water storage. The hypothesis of this study was that a Red Latosol (Oxisol), in summer and winter crops sequences under no-tillage system, can have its soil water storage influenced by changes in soil physical properties and digital tensiometer can be used to measure soil water matric potential. This study aimed to measure the soil matric potential using both mercury and digital tensiometers and to evaluate the soil water storage and physical properties on summer and winter crops sequences under no-tillage system. A completely randomized block was designed with three replications on a strips plan. The treatments were the combination of three summer crops sequences (soybean/maize rotation, corn and soybean monocultures) and seven winter crops (maize, sunflower, oilseed radish, millet, pigeon pea, sorghum and sunn hemp). Tensiometers were installed at a depth of 0.20; 0.40; 0.60 meters. Bulk density and pores distribution curves were determined from layers 0-0.1 and 0.1-0.2 depth and water infiltration at the soil surface. The data were submitted to variance analysis and means were compared by the Tukey test. The hypothesis was confirmed, therefore digital tensiometer can be used to measure soil water matric potential. The results showed no difference regarding soil water storage in summer crops sequences, especially after a period associated with lower water availability. Soil porosity and bulk density were not influenced by summer and winter crops sequences. The results indicated that the pores with diameter between 0,075 - 0,05 e 0,03 - 0,0375 mm from layer 0-0.1 m differed on summer crops sequences. No difference was observed by pores distribution curves between summer and winter crops sequences. The largest water infiltration occurred under the soybean monocultures plot

abstract: Lithium ion batteries prepared with a ceramic separator, have proven to possess improved safety, reliability as well as performance characteristics when compared to those with polymer separators which are prone to thermal runaway. Purely inorganic separators are highly brittle and expensive. The electrode-supported ceramic separator permits thinner separators which are a lot more flexible in comparison. In this work, it was observed that not any α-alumina could be used by the blade coating process to get a good quality separator on Li4Ti5O12 (LTO) electrode. In this work specifically, the effect of particle size of α-alumina, on processability of slurry was investigated. The effect of the particle size variations on quality of separator formation was also studied. Most importantly, the effect of alumina particle size and its distribution on the performance of LTO/Li half cells is examined in detail. Large-sized particles were found to severely limit the ability to fabricate such separators. The α-alumina slurry was coated onto electrode substrate, leading to possible interaction between α-alumina and LTO substrate. The interaction between submicron sized particles of α-alumina with the substrate electrode pores, was found to affect the performance and the stability of the separator. Utilizing a bimodal distribution of submicron sized particles with micron sized particles of α-alumina to prepare the separator, improved cell performance was observed. Yet only a specific ratio of bimodal distribution achieved good results both in terms of separator formation and resulting cell performance. The interaction of α-alumina and binder in the separator, and its effect on the performance of substrate electrode was investigated, to understand the need for bimodal distribution of powder forming the separator. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2017

Cette étude propose une unification des formulations mono- et multi-moments de la distribution granulométrique des pluies (DSD pour « drop size distribution ») proposées dans la littérature dans le cadre des techniques de mise à l’échelle (scaling). On considère dans un premier temps que la DSD normalisée par la concentration en gouttes (Nt, moment d'ordre 0 de la DSD) peut s’écrire comme une fonction de densité de probabilité (ddp) du diamètre normalisé par un diamètre caractéristique (Dc). Cette ddp, notée g(x) avec x=D/Dc, aussi appelé distribution générale, semble être bien représentée par une loi gamma à deux paramètres. Le choix d’un diamètre caractéristique particulier, le rapport des moments d’ordre 4 et 3, conduit à une relation d’auto-consistance entre les paramètres de la fonction g(x). Deux méthodes différentes, fondées sur 3 moments particuliers de la DSD (M0, M3 et M4) ou bien sur des moments multiples (de M0 à M6) sont proposées pour l’estimation des paramètres et ensuite évaluées sur 3 ans d’observations de DSD recueillies à Alès dans le cadre de l'Observatoire Hydrométéorologique Méditerranéen Cévennes-Vivarais (OHMCV). Les résultats révèlent que: 1) les deux méthodes d’estimation des paramètres ont des performances équivalentes; 2) malgré la normalisation, une grande variabilité de la DSD est toujours observée dans le jeu de données mis à l’échelle. Ce dernier point semble résulter de la diversité des processus micro-physiques qui conditionnent la forme de la DSD.Cette formulation est ensuite adaptée pour une mise à l’échelle avec un ou deux moments de la DSD en introduisant des modèles en loi puissance entre des moments dits de référence (par exemple l’intensité de la pluie R et / ou le facteur de réflectivité radar Z) et les moments expliqués (concentration en gouttes Nt, diamètre caractéristique Dc). De manière analogue à la première partie du travail, deux méthodes sont proposées pour estimer des paramètres climatologiques des DSD mises à l’échelle par un ou deux DSD moment(s). Les résultats montrent que: 1) la méthode d'estimation a un impact significatif pour la formulation de mise à l'échelle par un seul moment; 2) le choix du moment de référence dépend des objectifs d’étude: par exemple, le modèle mis à l'échelle par des moments d'ordre élevé produit une bonne performance pour les grosses gouttes mais pas pour les petites; 3) l’utilisation de deux moments au lieu d’un seul améliore significativement la performance du modèle pour représenter les DSD.Notre modèle est ensuite appliqué pour analyser la variabilité inter- événementielle selon trois paramètres (Nt, Dc et μ, ce dernier paramètre µ décrivant la forme de la fonction gamma). Différentes séquences de pluie ont été identifiées de façon subjective pour l’événement pluvieux intense des 21-22 octobre 2008 par des changements brusques des moments et/ou paramètres dans les séries temporelles correspondantes. Ces phases de pluie sont liées à des processus météorologiques différents. Une relation préliminaire est établie entre les observations radar et la variation des paramètres des DSD au sol telle que mesurée par le disdromètre. Les formulations de mise à l’échelle sont également appliquées pour des estimations des densités de flux d’énergie cinétique des précipitations à partir de l'intensité de la pluie et / ou de la réflectivité radar. Les résultats confirment que l’utilisation de deux moments (R et Z) améliore significativement les performances de ces modèles, malgré les caractéristiques d'échantillonnage très différentes des radars et des pluviomètres. Cette application ouvre des perspectives intéressantes pour la spatialisation de l’énergie cinétique des pluies dans le cadre des études sur le pouvoir érosif des pluies. / This study offers a unified formulation for the single- and multi-moment raindrop size distributions (DSD), which were proposed in the framework of scaling analysis in the literature. The key point is to consider the DSD scaled by drop concentration (Nt, 0th order DSD moment), as a probability density function (pdf) of raindrop diameter scaled by characteristic diameter (D/Dc). The Dc is defined as the ratio of the 4th to the 3rd DSD moment. A two-parameter gamma pdf model, with a self-consistency relationship, is found to be suitable for representing the scaling DSD formulation. For the purpose of parameter estimation, two different methods, based on three DSD moments (0th, 3rd and 4th moments) and multiple DSD moments (from 0th to 6th moments), are proposed and then evaluated through the 3-year DSD observations, collected at Alés within the activities of the Cévennes-Vivarais Mediterranean Hydrometeorological Observatory (CVMHO). The results reveal that: 1) the scaled DSD model parameterized by three moments (0th, 3rd and 4th moments) possesses a similar performance compared to that constructed by multiple DSD moments; 2) regardless the application of scaled technique, large variation is still exhibited in this climatological DSD scaled dataset. The scaled DSD formulation is, in a second step, adapted to the one- and two-moment scaling DSD formulations by introducing single and dual power-law models between the reference moments (e.g. rain rate R and/or radar reflectivity factor Z) and the explained moments (total concentration Nt, characteristic diameter Dc). Compared with previous DSD formulations presented in the literature, the presented approach explicitly accounts for the prefactors of the power-law models to produce a uniform and dimensionless scaled distribution, whatever the reference moment(s) considered. In the same manner, two methods based on 1) single or dual power-law models and 2) multiple DSD moments (from 0th to 6th moments), are proposed to estimate the climatological parameters in the one- and two-moment scaling DSD formulations. The results show that: 1) the estimation method has a significant impact on the climatological DSD formulation scaled by one moment; 2) the choice of the reference moment to scale DSD depends on the objectives of the research: e.g. the DSD model scaled by high order moment produces a good performance for large drops at the cost of a poor performance for the small ones; 3) using two scaling moments improves significantly the model performance to represent the natural DSD, compared to the one-moment DSD formulation. In terms of applications of scaling DSD model, the analysis of the inter-event variability is performed on the basis of the scaling formulation containing three parameters (Nt, Dc and µ describing the shape of the gamma function). Different rain phases can be identified by the sudden shifts of moments and parameters in DSD time series. It is found that these rain phases are well linked to different weather processes. And a preliminary relationship is established between the radar observations and DSD parameters. The climatological scaling DSD formulations are also used for the DSD reconstitutions and for rainfall kinetic energy flux density estimations by rain intensity and/or radar reflectivity factor. The results confirm that the application of two scaling moments (R and Z) improves significantly the performance of these models, regardless the different sampling characteristics between radar and raingauge.

Neste trabalho foi feita uma caracterização do material particulado coletado no Centro de Capacitação e Pesquisa em Meio Ambiente (CEPEMA) localizado na cidade de Cubatão, na Baixada Santista. As coletas ocorreram entre março de 2009 e novembro de 2010, utilizando amostradores de material particulado fino, grosso e inalável (Mini-Vol) e um impactador em cascata (MOUDI) para as várias frações do material particulado, durante oito campanhas experimentais. Foi realizada uma caracterização climatológica com os dados de temperatura, pressão atmosférica, umidade relativa, velocidade e direção do vento das estações da CETESB em Cubatão: Centro (10 anos), Vila Parisi (10 anos) e Vale do Mogi (4 anos). Os dados de chuva foram obtidos da Defesa Civil para a cidade de Santos. A maior parte das coletas de 2009 ocorreu em períodos em que houve precipitação, ao passo que as coletas de 2010 foram amostradas em períodos mais secos. O material particulado fino (MPF) teve concentrações médias de: 15,7 e 18,8 g m-3 em 2009 e 2010, respectivamente, quando coletado pelo MOUDI; e 15,8 e 23,6 g m-3, quando coletado pelo Mini-Vol. O material particulado grosso (MPG) teve concentrações médias de: 11,4 e 14,1 g m-3 em 2009 e 2010, respectivamente, quando coletado pelo MOUDI; e 18,9 e 13,4 g m-3, quando coletado pelo Mini-Vol. As análises de refletância mostraram que o Black Carbon está quase totalmente no MPF, chegando a 15% (20%) da massa do MPF quando coletado pelo MOUDI (Mini-Vol). Os íons dominantes são sulfato (SO42), nitrato (NO3), sódio (Na+), amônio (NH4+) e cálcio (Ca2+) e os elementos dominantes são enxofre (S), silício (Si) e ferro (Fe). As distribuições de tamanho mostram uma moda de nucleação bastante pronunciada para o S, K, Cl e P, indicando a contribuição de fontes antropogênicas e formação secundária do aerossol. As maiores concentrações de Si, Cl, Ca, Fe, Ca2+, NO3 e Na+ se encontram no MPG. Para o Cl e Na+, foram encontradas maiores concentrações nas amostras diurnas com vento do quadrante sul-sudoeste na estação do Centro, demonstrando a contribuição marinha. / This work evaluated the particulate matter (PM) collected at the Environmental Research and Training Center (CEPEMA) located in Cubatão City. Sampling was made between 2009, March and 2010, November for fine, coarse and inhalable aerosol (Mini-Vol) and for the various fractions of PM with a cascade impactor (MOUDI) during eight experimental campaigns. A climatological study was performed for temperature, pressure, relative humidity, wind speed and direction using data from CETESB stations: Centro (10 years), Vila Parisi (10 years) and Vale do Mogi (4 years). Precipitation data was obtained from the Civil Defense for the city of Santos. Most samplings made during 2009 were concomitant with rainy days, whereas 2010 samplings were made in drier periods. Fine particulate matter (FPM) had average concentrations of: 15.7 and 18.8 g m-3 in 2009 and 2010, respectively, with MOUDI and 15.8 and 23.6 g m-3, with Mini-Vol. Coarse Particulate Matter (CPM) had average concentrations of: 11.4 and 14.1 g m-3 in 2009 and 2010, respectively, with MOUDI, and 18.9 and 13.4 g m-3, with Mini-Vol. Reflectance analysis showed that the Black Carbon is almost completely in the FPM, reaching up to 15 % (20 %) of the FPM mass when sampled with MOUDI (Mini-Vol). Dominant ions are sulfate (SO42-), nitrate (NO3-), sodium (Na+), ammonium (NH4+) and calcium (Ca2+) and the dominant elements are sulfur (S), silicon (Si) and iron (Fe). The size distributions shows a very pronounced nucleation mode for the S, K, P and Cl, indicating the contribution of anthropogenic sources and secondary aerosol formation. The highest concentrations of Si, Cl, Ca, Fe, Ca2+, NO3- and Na+ are in CPM. For Cl- and Na+, major concentrations were found in samples with diurnal south-southwest wind indicating marine aerosol contribution.

The purpose of this study was to collect baseline data of juvenile scleractinian coral density, spatial variability, size variability, and species composition across the linear shore parallel hard bottom coral communities offshore Broward County, Florida. Adult coral population data was also collected and compared with that of the juvenile coral population to better understand the local coral demographics and potential factors that influence the population structure. The juvenile and adult coral data from the Broward County coral communities was then compared to a second study region 50 kilometers south to identify latitudinal changes in the coral population structure. The results of this study found that the densities and the list of coral species observed within the Broward County study region did fall within the range of densities found in other studies completed along the southern portion of the Florida Reef Tract and the Caribbean. Despite having similar species richness to other Caribbean studies, there was an overwhelming dominance of only a few species. This was also found in the adult coral population in the Broward study region. The densities of both the juvenile and adult coral populations were significantly positively correlated as well as their number of species observed across the sites in the Broward County study region. Additionally, the highly dominant species found in the juvenile population were in the adult population. Despite increasing coral density and diversity with decreasing latitude found in other studies conducted along the Florida Reef Tract, the results from this study were not as clear. Density of corals and the number of coral species did increase from north to south on the Outer reef however there was a significant decrease in the depth of the sample sites. On the Pavement habitat the density of juvenile corals increased from north to south however the number of coral species did not increase. The density and number of species of adult corals did not increase on the Pavement habitat with decreasing latitude as well making the results unclear.

[ES] La comprensión de los fenómenos físicos que acontecen en la región densa (también conocida como campo cercano) durante la atomización de los sprays ha sido una de las mayores incógnitas a la hora de estudiar sus aplicaciones. En el sector industrial, el rango de interés abarca desde toberas en aplicaciones propulsivas a sprays en aplicaciones médicas, agrícolas o culinarias. Esta evidente falta de conocimiento obliga a realizar simplificaciones en la modelización, provocando resultados poco precisos y la necesidad de grandes caracterizaciones experimentales en la fase de diseño. De esta manera, los procesos de rotura del spray y atomización primaria se consideran problemas físicos fundamentales, cuya complejidad viene dada como resultado de un flujo multifásico en un régimen altamente turbulento, originando escenarios caóticos. El análisis de este problema es extremadamente complejo debido a la ausencia sustancial de teorías validadas referentes a los fenómenos físicos involucrados como son la turbulencia y la atomización. Además, la combinación de la naturaleza multifásica del flujo y su comportamiento turbulento resultan en una gran dificultad para afrontar el problema. Durante los últimos 10 años, las técnicas experimentales han sido finalmente capaces de visualizar la región densa, pero la confianza, análisis y efectividad de dichos experimentos en esta región del spray todavía requiere de mejoras sustanciales. En este contexto, esta tesis trata de contribuir al entendimiento de estos procesos físicos y de proporcionar herramientas de análisis para estos flujos tan complejos. Para ello, mediante Direct Numerical Simulations se ha afrontado el problema resolviendo las escalas de movimiento más pequeñas, y capturando todas las escalas de turbulencia y eventos de rotura. Uno de los objetivos de la tesis ha sido evaluar la influencia de las condiciones de contorno del flujo entrante en la atomización primaria y en el comportamiento turbulento del spray. Para ello, se han empleado dos condiciones de contorno diferentes. En primer lugar se ha empleado una condición de contorno sintética para producir turbulencia homogenea a la entrada, simulando el comporamiento de la tobera. Una de las características más interesantes de este método es la posibilidad de retocar los parámetros dentro del algoritmo. En particular, la escala de longitud integral se ha variado para evaluar la influencia de las estructuras mas grandes de la tobera en la atomización primaria. El análisis de la condición de contorno sintética también ha permitido el diseño óptimo de simulaciones de las cuales se han derivado estadísticas turbulentas significativas. En este escenario, se han llevado a cabo estudios más profundos sobre la influencia de propiedades de las estructuras turbulentas como la homogeneidad y la anisotropía tanto en el espectro de los flujos como en las estadísticas de las gotas. Para tal fin, se han desarrollado metodologías novedosas para computar el análisis espectral y la estadística de las gotas Entre los resultados de este análisis destaca la independencia de la condición de contorno de entrada en las estadísticas de las gotas, mientras que por otra parte, recalca que las características turbulentas desarrolladas en el interior de la tobera afectan a la cantidad total de masa atomizada. Estas consideraciones se encuentran respaldadas por el análisis espectral realizado, mediante el cuál se concluye que la turbulencia multifásica comparte el comportamiento universal descrito por las teorías de Kolmogorov. / [CAT] La comprensió dels fenòmens físics que succeïxen en la regió densa (també coneguda com a camp pròxim) durant l'atomització dels sprays ha sigut una de les majors incògnites a l'hora d'estudiar les seues aplicacions. En el sector industrial, el rang d'interés comprén des de toveres en aplicacions propulsives a sprays en aplicacions mèdiques, agrícoles o culinàries. Esta evident falta de coneixement obliga a realitzar simplificacions en la modelització, provocant resultats poc precisos i la necessitat de grans caracteritzacions experimentals en la fase de disseny. D'esta manera, els processos de ruptura del spray i atomització primària es consideren problemes físics fonamentals, la complexitat dels quals ve donada com resultat d'un flux multifàsic en un règim altament turbulent, originant escenaris caòtics. L'anàlisi d'este problema és extremadament complex a causa de l'absència substancial de teories validades dels fenòmens físics involucrats com són la turbulència i l'atomització. A més, la combinació de la naturalesa multifàsica del flux i el seu comportament turbulent resulten en una gran dificultat per a afrontar el problema. Durant els últims 10 anys les tècniques experimentals han sigut finalment capaces de visualitzar la regió densa, però la confiança, anàlisi i efectivitat dels experiments en esta regió del spray encara requerix de millores substancials. En este context, esta tesi tracta de contribuir en l'enteniment d'estos processos físics i de proporcionar ferramentes d'anàlisi per a estos fluxos tan complexos. Per a això, per mitjà de Direct Numerical Simulations s'ha afrontat el problema resolent les escales de moviment més menudes, al mateix temps que es capturen totes les escales de turbulència i esdeveniments de ruptura. Un dels objectius de la tesi ha sigut avaluar la influència que les condicions de contorn del flux entrant tenen en l'atomització primària i en el comportament turbulent del spray. Per a això, s'han empleat dos condicions de contorn diferents. En primer lloc s'ha empleat una condició de contorn sintètica per a produir turbulència homogènia a l'entrada, simulant el comportament de la tovera. Una de les característiques més interessants d'este mètod és la possibilitat de retocar els paràmetres dins de l'algoritme. En particular, l'escala de longitud integral s'ha variat per a avaluar la influència de les estructures mes grans de la tovera en l'atomització primària. L'anàlisi de la condició de contorn sintètica també ha permés el disseny òptim de simulacions de les quals s'han derivat estadístiques turbulentes significatives. En este escenari, s'han dut a terme estudis més profunds sobre la influència de propietats de les estructures turbulentes com l'homogeneïtat i l'anisotropia tant en l'espectre dels fluxos com en les estadístiques de les gotes. Per a tal fi, s'han desenrotllat metodologies noves per a computar l'anàlisi espectral i l'estadística de les gotes. Entre els resultats d'esta anàlisi destaca la independència de la condició de contorn d'entrada en les estadístiques de les gotes, mentres que d'altra banda, es recalca que les característiques turbulentes desenrotllades en l'interior de la tovera afecten a la quantitat total de massa atomitzada. Estes consideracions es troben recolzades per l'anàlisi espectral realitzat, per mitjà del qual es conclou que la turbulència multifásica compartix el comportament universal descrit per les teories de Kolmogorov. / [EN] The understanding of the physical phenomena occurring in the dense region (also known as near field) of atomizing sprays has been long seen as one of the biggest unknown when studying sprays applications. The industrial range of interest goes from nozzles in combustion and propulsion applications to medical sprays, agricultural and food process applications. This substantial lack of knowledge is responsible for some important simplification in modeling, that often result to be inaccurate or simply partial, leading to the evident need of large experimental characterization during the design phase. In fact, the spray breakup and primary atomization processes are indeed fundamental problems of physics, which complexity results from the combination of a multiphase flow in a highly turbulent regime that leads to chaotic scenarios. The analysis of this problem is extremely problematic, due to a substantial lack of definitive theories about the physical phenomena involved, namely turbulence and atomization. Furthermore, the combination of the multiphase nature of the flow and its turbulent behavior makes substantially difficult to address the problem. Only within the last 10 years, experimental techniques have been capable of visualizing the dense region, but the experiments reliability, analysis and effectiveness in this region still requires vast improvements. In this scenario, this thesis aims to contribute in the understanding of these physical process and to provide analysis tools for these complex flows. In order to do so, Direct Numerical Simulations have been used for addressing the problem at its smallest scale of motion, while reliably capturing all turbulence scales and breakup events. The multiphase nature of the flow is accounted for by using the Volume of Fluid method. One of the goal of the thesis was to assess the influence of the inflow boundary conditions on the primary atomization and on the spray's turbulence behavior. In order to do so, two different boundary conditions were used. In a first place, a synthetic inflow boundary condition was used in order to produce a homogeneous turbulence inflow, simulating the nozzle behavior. One of the interesting features of this method was the possibility of tweaking the parameters within the algorithm. In particular, the integral length scale was varied in order to assess the influence of nozzle larger turbulent structures on the primary atomization. The analysis on the synthetic boundary condition also allowed to optimally design simulations from which derive meaningful turbulence statistics. On this framework, further studies were carried over on the influence of turbulent structures properties, namely homogeneity and anisotropy, on both the flows spectra and droplets statistics. In order to achieve this goal, novel procedures for both computing the flow spectra and analyzing droplets were developed and are carefully addressed in the thesis. The results of the analysis highlight the independence of droplets statistics from the inflow boundary condition, while, on the other hand, remarking how the total quantity of atomized mass is significantly affected by the turbulence features developed within the nozzle. This considerations are supported by the spectrum analysis performed, which also highlighted how multiphase turbulence shares the universal features described in Kolmogorov theories. / Crialesi Esposito, M. (2019). Analysis of primary atomization in sprays using Direct Numerical Simulation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/133975 / TESIS

<p>Evidence exists for the airborne transmission of contagious pathogens such as SARS-CoV-2, influenza A virus and <i>Mycobacterium</i> <i>tuberculosis</i> in indoor environments. These pathogens are carried in the respiratory droplets and transmitted through airborne route to infect individuals. An important element in risk assessment for pathogenic bioaerosol exposure is a determination of the inhaled deposited dose rate – the number of deposited pathogenic particles per minute – received by each respiratory region and the fractional reduction of dose rate by different material facemasks. This paper presents an aerosol physics-based modeling framework to estimate the fractional reduction of regional dose rate in diverse indoor healthcare environments. The fractional reduction of dose rate is a useful metric to evaluate the facemask effectiveness in reducing the inhaled dose rate. Data extraction of pathogenic bioaerosol size distributions and size-dependent facemask filtration efficiency curve combined with deposition fraction model become the baseline to calculate the fractional reduction of dose rate by 10 different facemasks. Facemask leakage is also considered for the realistic representation of its impact on reduction fraction as current studies focus on mask material filtration efficiency. This analysis considers how the fractional reduction of dose rate is influenced by the pathogenic bioaerosol size distribution, age-dependent respiratory parameters, age-specific deposition fraction, facemask filtration efficiency and mask leakage. Different factors drove variations in the reduction fraction of various sized-pathogenic bioaerosols received by each respiratory region for each age group. This framework can be a useful tool for decision-makers in evaluating the mask’s effectiveness in reducing deposition of pathogenic bioaerosols.</p>