In this thesis. a three dimensional heat transfer model of heated airflow through the upper human respiratory tract consisting of nasal, oral, trachea, and the first two generations of bronchi is developed using computational fluid dynamics simulation software. Various studies have been carried out in the literature investigating the heat and mass transfer characteristics in the upper human respiratory tract, and the study focuses on assessing the injury taking place in the upper human respiratory tract and identifying acute tissue damage based on level of exposure. The model considered is for the simultaneous oronasal breathing during the inspiration phase with high volumetric flow rate of 90/liters minute and a surrounding air temperature of 100 degrees centigrade. The study of the heat and mass transfer, aerosol deposition and flow characteristics in the upper human respiratory tract using computational fluid mechanics simulation requires access to a two dimensional or three dimensional model for the human respiratory tract. Depicting an exact model is a complex task since it involves the prolonged use of imaging devices on the human body. Hence a three dimensional geometric representation of the human upper respiratory tract is developed consisting of nasal cavity, oral cavity, nasopharynx, pharynx, oropharynx, trachea and first two generations of the bronchi. The respiratory tract is modeled circular in cross-section and varying diameter for various portions as identified in this study. The dimensions are referenced from the literature herein. Based on the dimensions, a simplified model representing the human upper respiratory tract is generated.This model will be useful in studying the flow characteristics and could assist in treatment of injuries to the human respiratory tract as well as help optimize drug delivery mechanism and dosages. Also a methodology is proposed to measure the characteristic dimension of the human nasal and oral cavity at the inlet/outlet points which are classified as internal measurements.

Este estudio es parte del proyecto FONDECYT N° 1120234 “Geodinámica y tendencia evolutiva del sistema litoral de la mega ensenada de Coquimbo: hacia una prognosis de amenazas naturales para escenarios de cambios ambientales endógenos y exógenos. / Memoria para optar al título de Geógrafo / Se estudia la transferencia de masa entre la desembocadura del río Limarí, bahía Tongoy y bahía Barnes a través de la integración de unidades costeras, identificando las formas de acumulación, las relaciones morfosedimentológicas en los grupos de formas existentes y el transporte de masa en el litoral. Para la identificación de las formas de acumulación en las áreas de estudio, fue necesario realizar una descripción geomorfológica, identificando formas fluviales, fluviomarinas, terrazas marinas y formas eólicas. Para el análisis de las relaciones morfosedimentológicas se hizo necesario realizar análisis granulométrico según los procedimientos de distribución textural y morfoscópico de arenas, además de la mineralogía. Para el transporte de masa litoral se utilizó técnicas cualitativas a través del análisis multitemporal del ambiente de depositación, en un rango temporal de 27 años, analizando imágenes satelitales LandSat de los años 1987,1997, 2004 y 2011. Los resultados alcanzados denotan el fuerte control estructural y la orientación dominantemente oblicua de las bahías como factores que posibilitan la sedimentación de este sistema litoral, operando los principios de efecto de ensenada en éstas. Se considera que la fuente de abastecimiento de las bahías Tongoy y Barnes proviene de la cuenca del río Limarí, pero es necesario también considerar otros medios de transporte de sedimentos que no necesariamente tiene relación con el río ni su zona de descarga. El análisis multitemporal de las imágenes satelitales refleja que la transferencia de masa entre los diferentes sistemas se debe en el período reciente a condiciones que sobrepasen el umbral de transporte de sedimentos, esas condiciones se deben al aumento en la intensidad y torrencialidad de las precipitaciones. Las formas que reflejan cambios en los ambientes de depositación corresponden a flechas litorales y campos dunares las cuales son áreas sensibles a los aportes de sedimentos entre los sistemas. / It is studied that mass transfer between the Limarí river mouth, Tongoy bay and Barnes bay across of the integration of costal units, identifying accumulation forms, morphosedimentological, relations in the groups of existing forms and the mass transport in the coast. For identifying forms of accumulation in the areas of study, it was necessary to make a geomorphological description, identifying fluvial forms, river-marine, marine terraces and aeolian forms. For the analysis of morphosedimentological relations, it became necessary to perform granulometric analysis according to the procedures of textural distribution and sand morphocopic, including the mineralogy. For the transport of littoral mass we used qualitative techniques through the multitemporary analysis the depositional environment, a temporary range of 27 years, analyzing Landsat satellite images of the years 1987, 1997, 2004 and 2011. The results show the strong structural control and oblique orientation dominantly of the bays as factors that enable the sedimentation of the coastal system, operating the effect of cove principles in them. It is considered that the source of supply for Tongoy and Barnes bays comes from Limarí river basin, but it is also necessary to consider other transport means of sediments that does not necessarily have relation to the river or its discharge zone. The multi-temporal analysis of satellite images reflects that the mass transfer between the different systems ocurred in the recent period due to conditions that exceeded the threshold of sediment transport, these conditions are due to increase in the intensity and heavy rainfall. The forms that reflect changes in the deposition environments correspond to coastal arrows and dune fields which are sensitive areas to the contributions of sediments between systems.

In situ chemical oxidation (ISCO) using permanganate has been increasingly applied to deplete mass from dense nonaqueous-phase liquid (DNAPL) source zones. However, uncertainty in the performance of ISCO on DNAPL contaminants is partially attributable to a limited understanding of interactions between the oxidant, subsurface hydrology, and DNAPL mass transfer, resulting in failure to optimize ISCO applications. To investigate these interactions, a factorial design experiment was conducted using one-dimensional flow through tube reactors to determine how groundwater velocity, permanganate concentration, and DNAPL type affected DNAPL mass depletion rates. DNAPL mass depletion rates were found to increase with increasing groundwater velocity, or increasing oxidant concentration. An interaction occurred between the two factors, where high oxidant concentrations had little impact on mass depletion rates at high velocities. High oxidant concentration systems experienced gas generation. Mass depletion rates were fastest at high velocities, but required additional oxidant mass and pore volume addition to achieve complete mass depletion. Lower-velocity systems were more efficient with respect to oxidant mass and pore volume requirements, but mass depletion rates were reduced.

Biofilms of the bovine rumen bacterium Actinobacillus succinogenes have demonstrated their exceptional capabilities as biocatalysts for high productivity, titre and yield production of succinic acid (SA). Succinic acid is set to become a significant building block chemical in the biobased economy. Although substantial progress has been made towards understanding the productive aspect of this microorganism with regard to its metabolic limits and performance on unrefined biorefinery stream substrates, more research is still required to address other challenges. One aspect is to understand how the biofilm biocatalyst is affected by bioreactor conditions, which would help in developing stable and highly active biofilms. For this reason the aim of this thesis was (i) to characterise how the accumulation of acid metabolites in continuous operation impacts A. succinogenes biofilms with respect to biofilm development, biofilm structure and cell activity within the biofilm, (ii) to show how shear conditions in the fermenter can be used to manipulate the biofilm structure and viable cell content of biofilms, leading to improved cell-based succinic acid productivities, and lastly (iii) to investigate the internal mass transfer effects on biofilm performance, further showing the role played by differences in shear and acid accumulation conditions in this respect. The first part of the study addressed the interaction between the biofilm and the accumulation of metabolites produced. The results showed that biofilms of A. succinogenes develop rapidly and with high activity when cultivated under low product accumulation (LPA) conditions (< 10 g L-1 SA). High product accumulation (HPA) conditions considerably slowed down biofilm development, and increased cell mortality. Under HPA conditions some cells exhibited severe elongation while maintaining a cross-sectional diameter like the rod/cocci-shaped cells predominantly found in LPA conditions. The elongated cells formed in HPA conditions were found to be more viable and thus more resistant than the clusters of rod-shaped or cocci-shaped cells. The global microscopic structure of the HPA biofilms also differed significantly from that of the LPA biofilms. Although both exhibited shedding after 4 days of growth, the LPA biofilms were more homogenous (less patchy), thicker and had high viability throughout the biofilm depth. In the second part of the study, two custom-designed bioreactors were used to evaluate the effect of shear on the biofilms. The first bioreactor allowed for in situ removal of small biofilm samples used for microscopic imaging. The second bioreactor allowed for complete removal of all biofilm and was used to analyse biofilm composition and productivity. Results clearly indicated that high shear biofilm cultivation in LPA conditions has beneficial morphological, viability and cell-based productivity characteristics. The smooth, low-porosity biofilms obtained under high shear and LPA conditions had an average cell viability of 79% (over a 3-day cultivation period) compared with the low shear value of 57%, also developed under LPA conditions. The EPS content of the high shear biofilm was 58% compared with 7% of the low shear equivalent. The cell-based (EPS excluded) succinic acid productivity for the high shear biofilm was 2.4 g g-1DCW h-1 compared with the 0.8 g g-1DCW h-1 for the low shear biofilm. This threefold increase in productivity obtained from the second bioreactor corresponded to the cell viability differences obtained from the first bioreactor. Clear evidence was provided for shear-induced shaping of the biofilm which resulted in improved volumetric glucose turnover attributes within the biofilm matrix. The last section of the study investigated internal mass transfer effects in biofilm fermentations of Actinobacillus succinogenes by performing batch fermentations using attached and resuspended biofilms as biocatalysts. In the latter, the biofilms were resuspended after initial development to simulate mass transfer-free fermentations. Intrinsic kinetics for succinic acid production obtained from resuspended fermentations predicted faster production rates than for the attached biofilm runs (biofilm thicknesses in the range of 120–200 µm), indicating internal mass transfer limitations. A developed biofilm reaction diffusion model gave good prediction of attached biofilm batch operation results by accounting for internal mass transfer in the biofilm. Biofilm effectiveness factors ranged from 75% to 97% for all batches at the inception of batch conditions, but increased with the progression of batch operation due to the increased succinic acid titres which inhibited the production rates. Analysis of pseudo-steady-state continuous fermentation data from the literature, as well as from the second part of the study, using the model developed, showed that active biofilm thickness and effectiveness factors were dependent on the shear conditions and succinic acid titres in the biofilm reactors. A simplified algorithm was developed to estimate the pseudo-steady-state glucose penetration and biofilm effectiveness of A. succinogenes biofilms without the requirement to solve the overall mass transfer model. The results clearly showed that internal mass transfer needs to be considered in biofilm fermentations involving A. succinogenes as high biomass concentrations may not always equate to increased productivities if mass transfer effects dominate. / Thesis (PhD)--University of Pretoria, 2020. / NRF / Chemical Engineering / PhD / Unrestricted

There exist several different numerical models for predicting bubble coalescence and breakup using computational fluid dynamics (CFD). Various combinations of these models will be employed to model a bioreactor process in a stirred reactor tank. A mass transfer coefficient, Kla, has been calculated and compared to those found experimentally by Thermo-Fisher Scientific, to validate the accuracy of currently available mathematical models for population balance equations. These include various combinations of bubble breakup and coalescence models coupled with the calculation of mass transfer coefficients.

Binary mass transfer is a common phenomenon is stellar astrophysics. If the mass transfer proceeds on dynamical timescale, the binary can undergo a catastrophic interaction accompanied by tremendous loss of mass, angular momentum, and energy. This so-called common envelope evolution phase is a crucial step in the formation of close binaries composed of compact objects (white dwarfs, neutron stars, black holes), which includes progenitors of gravitational wave sources de- tected by LIGO. By improving existing models of binary mass transfer we can correct the predictions of common envelope evolution and constraint the rates of close binaries composed of compact objects. In this work, we introduce new model of binary mass transfer. We will treat the mass transfer as a special case of stellar wind. We will rely on the assumption that the Roche potential sets up a de Laval nozzle around the first Lagrange point. The mass is then transferred through the nozzle. Our binary mass transfer model predicts mass transfer rates in the same order of magnitude as the standard models which use the Bernoulli's law. But the advantage of our model is that it is extendable to account for radiation.

Predicting the dissolution rates of immiscible contaminants in groundwater is crucial for developing environmental remediation strategies, but quantitative modeling efforts are inherently subject to multiple uncertainties. These include unknown residual amounts of non-aqueous phase liquids (NAPL) and source zone dimensions, inconsistent historical monitoring of contaminant mass discharge, and the mathematical simulation of field-scale mass transfer processes. Effective methods for simulating NAPL dissolution must therefore be able to assimilate a variety of data through physical and scalable mass transfer parameters to quantify and reduce site-specific uncertainties. This investigation coupled upscaled and numerical mass transfer modeling with uncertainty analyses to understand and develop data-assimilation and parameter-scaling methods for characterizing NAPL source zones and predicting depletion timeframes. Parameters of key interest regulating kinetic NAPL persistence and contaminant fluxes are residual mass and saturation, but neither can be measured directly at field sites. However, monitoring and characterization measurements can constrain source zone dimensions, where NAPL mass is distributed. This work evaluated the worth of source zone delineation and dissolution monitoring for estimating NAPL mass and mass transfer coefficients at multiple scales of spatial resolution. Mass transfer processes in controlled laboratory and field experiments were analyzed by simulating monitored dissolved-phase concentrations through the parameterization of explicit and lumped system properties in volume-averaged (VA) and numerical models of NAPL dissolution, respectively. Both methods were coupled with uncertainty analysis tools to investigate the relationship between data availability and model design for accurately constraining system parameters and predictions. The modeling approaches were also combined for reproducing experimental bulk effluent rates in discretized domains, explicitly parameterizing mass transfer coefficients at multiple grid scales. Research findings linked dissolved-phase monitoring signatures to model estimates of NAPL persistence, supported by source zone delineation data. The accurate characterization of source zone properties and kinetic dissolution rates, governing NAPL longevity, was achieved by adjusting model parameterization complexity to data availability. While multistage effluent rates accurately constrained explicit-process parameters in VA models, spatially-varying lumped-process parameters estimated from late dissolution stages also constrained unbiased predictions of NAPL depletion. Advantages of the numerical method included the simultaneous assimilation of bulk and high-resolution monitoring data for characterizing the distribution of residual NAPL mass and dissolution rates, whereas the VA method predicted source dissipation timeframes from delineation data alone. Additionally, comparative modeling analyses resulted in a methodology for scaling VA mass transfer coefficients to simulate NAPL dissolution and longevity at multiple grid resolutions. This research suggests feasibility in empirical constraining of lumped-process parameters by applying VA concepts to numerical mass transfer and transport models, enabling the assimilation of monitoring and source delineation data to reduce site-specific uncertainties. / Doctor of Philosophy / Predicting the dissolution rates of immiscible contaminants in groundwater is crucial for developing environmental restoration strategies, but quantitative modeling efforts are inherently subject to multiple uncertainties. These include unknown mass and dimensions of contaminant source zones, inconsistent groundwater monitoring, and the mathematical simulation of physical processes controlling dissolution rates at field scales. Effective simulation methods must therefore be able to leverage a variety of data through rate-limiting parameters suitable for quantifying and reducing uncertainties at contaminated sites. This investigation integrated mathematical modeling with uncertainty analyses to understand and develop data-driven approaches for characterizing contaminant source zones and predicting dissolution rates at multiple measurement scales. Parameters of key interest regulating the lifespan of source zones are the distribution and amount of residual contaminant mass, which cannot be measured directly at field sites. However, monitoring and site characterization measurements can constrain source zone dimensions, where contaminant mass is distributed. This work evaluated the worth of source zone delineation and groundwater monitoring for estimating contaminant mass and dissolution rates at multiple measurement scales. Rate-limiting processes in controlled laboratory and field experiments were analyzed by simulating monitored groundwater concentrations through the explicit and lumped representation of system properties in volume-averaged (VA) and numerical models of contaminant dissolution, respectively. Both methods were coupled with uncertainty analysis tools to investigate the relationship between data availability and model design for accurately constraining system parameters and predictions. The approaches were also combined for predicting average contaminant concentrations at multiple scales of spatial resolution. Research findings linked groundwater monitoring profiles to model estimates of contaminant persistence, supported by source zone delineation data. The accurate characterization of source zone properties and contaminant dissolution rates was achieved by adjusting model complexity to data availability. While monitoring profiles indicating multi-rate contaminant dissolution accurately constrained explicit-process parameters in VA models, spatially-varying lumped parameters estimated from late dissolution stages also constrained unbiased predictions of source mass depletion. Advantages of the numerical method included the simultaneous utilization of average and spatially-detailed monitoring data for characterizing the distribution of contaminant mass and dissolution rates, whereas the VA method predicted source longevity timeframes from delineation data alone. Additionally, comparative modeling analyses resulted in a methodology for scaling estimable VA parameters to predict contaminant dissolution rates at multiple scales of spatial resolution. This research suggests feasibility in empirical constraining of lumped parameters by applying VA concepts to numerical models, enabling a comprehensive data-driven methodology to quantify environmental risk and support groundwater cleanup designs.

Bubble columns are multiphase contactors, which are often used for the operation of multiphase reactions. These reactors are characterized by large interfacial areas, intense mixing in the column and dynamic flow structures. For the design of bubble columns numerous empirical correlations for hydrodynamic and mass transfer parameters exist, which however, only cover a specific design range, e.g. column diameter and reaction system. Furthermore, they are often based on integral measurements. High deviations occur especially at moderate and high gas holdup, since fluid dynamics and mass transfer are essentially determined by local effects, which has received little attention so far due to lack of appropriate measurement techniques. For this reason the design of bubble columns is carried out with considerable safety margins. Therefore, bubble columns have a high potential for savings in terms of efficiency and operating costs if the unterstanding of the hydrodynamics and mass transfer in bubble columns is improved. The fluid dynamics in bubble columns are essentially characterized by the bubble size distribution and with increasing gas holdup by enhanced bubble interaction, which leads to intense motion in the liquid phase. A cross-scale study of the fluid dynamics is necessary to better understand the factors influencing the global fluid dynamics and to optimize the design of bubble columns. The major limitations in the experimental investigation of dense bubbly flow are the available measurement techniques. As the fraction of the dispersed phase increases, the optical accessibility decreases and limits the selection of appropriate measurement techniques. This work deals with the experimental study of fluid dynamics and mass transfer with chemical reaction using tomographic measurement techniques. The experiments were performed in a cylindrical bubble column with 0.10 m inner diameter. The gas phase fluid dynamics were studied by means of ultrafast X-ray computed tomography (UFXCT). Additionally, the minimally intrusive wire-mesh sensor was qualified to assess chemical species concentrations during chemical absorption of CO2 and to derive local mass transfer related parameters. Among the global description of the fluid dynamics also local parameters of the dispersed phase were extracted. Advanced post-processing algorithms for ultrafast X-ray CT data allow a more accurate determination of the Sauter diameter and interfacial area due to the extraction of the bubbles surface area. The interaction of bubbles within dense bubbly flow was studied by determining and evaluating distance parameters of the bubbles. Based on that, the near order of bubbles was studied and conclusions on their preferential arrangement in dense bubbly flows were derived. Furthermore, the fluid dynamics and mass transfer were studied in the presence of a chemical reaction. For this purpose experiments on the chemical absorption of CO2 in sodium hydroxide solution were performed at various gas flow rates and initial pH values of the solution. The change of the fluid dynamics and the conversion of the chemical species is analyzed for different experimental conditions. A core topic of the present work is the determination of concentration of a chemical species during chemical absorption of CO2. Within this work, the wire-mesh sensor was qualified for this new field of application and was used to determine cross-sectional data of the species conversion. Through combined use of the wire-mesh sensor and ultrafast X-ray CT an extensive data base on the chemical absorption of CO$_2$ was obtained, which can be used for numerical validation of bubbly flows with gas holdups < 0.17 / Blasensäulen sind in der chemischen Industrie sehr häufig genutzte Kontaktapparate für die Durchführung von Mehrphasenreaktionen. Sie zeichnen sich durch eine hohe Gas-Flüssig-Aus-tauschfläche, starke Vermischung und dynamische Strömungsstrukturen aus. Bisher basiert die Auslegung von Blasensäulen vorrangig auf empirischen Korrelationen. Hohe Abweichungen dieser Korrelationen treten vor allem bei moderaten und hohen Gasgehalten auf, da die Fluiddynamik und der Stofftransport wesentlich durch lokale Effekte bestimmt sind, die bisher aufgrund fehlender Messtechnik nur wenig Beachtung finden. Aus diesem Grund erfolgt die bisherige Auslegung von Blasensäulenreaktoren mit erheblichen Sicherheitszuschlägen. Daraus lässt sich ableiten, dass Blasensäulen in Bezug auf deren Effizienz und die Höhe der Betriebskosten ein enormes Einsparungspotential aufweisen, wenn das Verständnis von Hydrodynamik und Stofftransport in Blasensäulen verbessert wird. Die Fluiddynamik in Blasensäulen wird wesentlich durch die Blasengrößenverteilung und bei steigendem Gasgehalt durch die durch zunehmende Blaseninteraktion induzierte Flüssigkeitsbewegung charakterisiert. Eine skalenübergreifende Untersuchungen der Fluiddynamik ist erforderlich, um die Einflussfaktoren der globalen Fluiddynamik besser verstehen zu können und die Auslegungsgleichungen optimieren zu können. Die größte Limitierung der experimentellen Untersuchung von dichten Blasenströmung stellt die verfügbare Messtechnik dar. Mit zunehmenden Anteil der Dispersphase nimmt die optische Zugänglichkeit ab und schränkt die Möglichkeiten bei der Auswahl geeigneter Messtechniken ein. Diese Arbeit beschäftigt sich mit der experimentellen Untersuchung der Fluiddynamik und des Stofftransports bei chemischer Reaktion mit Hilfe tomographischer Messverfahren. Die Experimente wurden in einer zylindrischen Blasensäule mit 0,10 m Durchmesser durchgeführt. Die Fluiddynamik der Gasphase wurde mit Hilfe der ultraschnellen Röntgen-Computertomographie (UFXCT) untersucht. Zusätzlich wurde der minimal-intrusive Gittersensor qualifiziert, um die Konzentrationen einer relvanten chemischen Spezies während der chemischen Absorption von CO2 zu bestimmen und stofftransportbezogene Parameter auf lokaler Ebene berechnen. Neben der räumlich und zeitlich gemittelten Beschreibung der Fluiddynamik wurden auch lokale Parameter der dispersen Phasen bestimmt. Fortgeschrittene Auswertungsalgorithmen ermöglichen eine genauere Berechnung des Sauterdurchmessers und der Phasengrenzfläche durch direkte Bestimmung der Blasenoberfläche. Die Interaktion von Blasen in der dichten Blasenströmung wurde durch die Berechnung von Abstandsparametern untersucht. Dies ermöglicht die Analyse der Nahordnung von Blasen und lässt damit Rückschlüsse auf deren bevorzugte Anordnung in dichten Blasenströmungen zu. Darüber hinaus wurden die Fluiddynamik und zum Stofftransport in Gegenwart einer chemischen Reaktion untersucht. Dazu wurden Experimente zur chemischen Absorption von CO2 n Natronlauge in der Blasensäule bei verschiedenen Gasdurchsätzen und unterschiedlichen initialen pH-Werten der Lösung durchgeführt. Die Veränderung der Fluiddynamik der Gasphase und die Umwandlung der chemischen Spezies wurden unter verschiedenen Betriebsbedingungen analysiert. Ein Kernthema der Arbeit stellt die Erfassung der Konzentration einer chemischen Spezies während der chemischen Absorption dar. Dazu wurde im Rahmen dieser Arbeit der Gittersensor für dieses neue Anwendungsgebiet qualifiziert und eingesetzt, um querschnittsaufgelöste Daten über den Verbrauch der charakteristischen Spezies zu ermitteln. Durch den kombinierten Einsatz der Gittersensormesstechnik und der ultraschnellen Röntgentomographie wurden umfangreiche Daten zur Hydrodnamik und zum Stofftransport während der chemischen Absorption von CO2 erhalten. Diese stellen eine umfassende Datenbasis zur numerischen Validierung von Blasenströmungen mit Gasgehalten bis zu 17% dar.

[pt] Foi estudado a subida de bolhas de ar formadas diretamente dentro de uma camada de água destilada disposta a baixo de um fluido Newtoniano superior imiscível. Modificou-se as propriedades do fluido superior, obtendo-se seis fluidos diferentes e foi verificado a diferentes e foi verificado a diferença de comportamento de subida da bolha de ai em cada um desses fluidos. Notaram-se três tipos de comportamento durante ascensões em função do tamanho de bolha: a) Bolhas pequenas: ficam retidas algum tempo na interface para subir em seguida sem carregar nenhuma película de água da fase mais densa. Limite: D menor que 3,4 mais ou menos 0,2 mm mais ou menos 0,2 mm. b) Bolhas médias atravessam a interface líquida e carregam uma película da fase mais densa envolvendo a bolha de ar até a superfície livre do líquido superior, que não deve estar a uma altura inferior a 50 D, de maneira que nos assegure estar a superfície livre na faixa de deslocamento permanente. Limite: 3,4 mais ou menos 0,2 mm menor que D menor que 5,5 mais ou menos 0,3 mm c) Bolhas grandes: atravessam a interface e carregam a película até uma certa altura, quando se desprende da bolha de ar. Limite: D maior que 5,5 mais ou menos 0,3 mm Os limites encontrados independiam da viscosidade do meio superior. Para todos os líquidos foram os mesmos. Fixou-se mais objetivamente o estudo sobre os comportamentos b e c, e foi verificada a grande influência que a película de água exerce sobre a bolha. A modificação do valor da viscosidade tem uma influência sobre (a) a forma pela qual as bolhas atravessam a interface; (b) a forma pela qual as bolhas carregam a a película de água e (c) o destacamento entre a bolha e a película de água. Para fluido de lata viscosidade, a passagem é lenta e forma uma coluna líquida que se quebra em gotículas e o destacamento da película de água e suave. Para líquidos de pequena viscosidade o comportamento é oposto. A passagem pela interface é abrupta e o destacamento é violento. As curvas criadas para descrever a altura em que ocorria o desprendimento em relação ao diâmetro das bolhas para cada um dos líquidos superiores estudados, mostram que para um mesmo diâmetro, a diminuição da viscosidade causa um desprendimento a uma altura maior. Para uma mesma viscosidade de (mesmo líquido) o aumento do diâmetro corresponde a uma menor altura de desprendimento entre a bolha de ar e a película de água. As experiências feitas para medir a transferência de massas de água pela bolha de ar permitiram que verificássemos que uma quantidade maior de água é transferida quando o líquido superior tem alta viscosidade. Da mesma maneira o aumento de diâmetro de bolha implica em um aumento de transferência de massa. / [en] The rising of air bubbles released in distilled water beneath na imiscible Newtoniam fluid was studied in an imiscible Newtonian fluid was fluid ws studied in this work. The properties of the upper fluid were modified and rising of the bubble in each of the six different fluids was noted. There were thereee types of behavior witch were a function of the bubbles diameter: a)Small size bubbles: remained temporary ar the interface and then rise upper phase without any perceptible water element envelopping them Limit: D less than 3,4 more or less 0,2 mm b)Medium size bubbles: passes directly through the liquid-liquid interface and now enveloped with a waer layer of variable thikness rise in the upper phase and reach the free surface with the coating intact. The medium size bubbles rise at a distance of over 50D. Limit: 3,4 more or less 0,2 mm less than D less than 5,5 more or less 0,3 mm c)Large size bubbles: passed directly trrough the liquid interface. At a certain height above the interface the water layer datached from the air bubbles. Limit: D more than 5,5 more or less 0,2 mm The critical diameters were found to depend on the viscosity of the upper phase. This study was restrict to cases b and c where the large influence of the envelopping water layer datached from the air bubble. This study was restrict to cases b and c where the large influence of the envelopping water layer over the air bubble was observed. The change of the visconsity value has an influence on : (a) the way in which the bubble and the water layer and; (b) the way in which the bubble lift the the water layer and (c) the detachment between the bubble and the water layer. For fluid of high viscosity, the passage is slow and makes a liquid colimn that breakes into passage is slow and makes a liquid column that breakes into droplets and the detachmenr of the water layer is smooth. For liquid os samall viscosity this transitional behavior is the oppoite. The detachment is violent. The curves which describe the height of detachment as function of the diameter, for each one fo the upper liquids show that: for a given diameter also have a inverse variation. The investigation made to measure the water mass transfer phenomena caused by the bubbles showed that the mass transfer will be larger for the higher viscosity fluides and the larger diameter bubbles.

<p>Kyle Weideman PhD Thesis</p>