Dissertations / Theses on the topic 'Droplet size distributions'

Spray models are increasingly becoming the principal tools in the design and development of gas turbine combustors. Spray modeling requires a knowledge of the liquid atomization process, and the sizes and velocities of subsequently formed droplets as initial conditions. In order to have a better understanding of the liquid atomization process,the breakup characteristics of plane liquid sheets in co-flowing gas streams are investigated by means of linear and nonlinear hydrodynamic instability analyses. The liquid sheet breakup process is studied for initial sinuous and varicose modes of disturbance. It is observed that the sheet breakup occurs at half-wavelength intervals for an initial sinuous disturbance and at full-wavelength intervals for an initial varicose disturbance. It is also found that under certain operating conditions, the breakup process is dictated by the initial varicose disturbance compare to its sinuous counterpart. Further, the breakup process is studied for the combined mode and it is found that the sheet breakup occurs at half- or full-wavelength intervals depending on the proportion of the individual sinuous and varicose disturbances. In general, the breakup length decreases with the increase in the Weber number, gas-to-liquid velocity and density ratios. A predictive model of the initial droplet size and velocity distributions for the subsequently formed spray is also formulated here. The present model incorporates the deterministic aspect of spray formation by calculating the breakup length and the mass-mean diameter and the stochastic aspect by statistical means through the maximum entropy principle based on Bayesian entropy. The two sub-models are coupled together by the various source terms signifying the liquid-gas interaction and a prior distribution based on instability analysis, which provides information regarding the unstable wave elements on the two liquid-gas interfaces. Experimental investigation of the breakup characteristics of the liquid sheet is performed by a high speed CCD camera and the measurement of the initial droplet size and distributions is conducted by phase-Doppler interferometry. Good agreement of the theoretical breakup length with the experiment is obtained for a planar, an annular and a gas turbine nozzle. The predicted initial droplet size and velocity distributions show reasonably satisfactory agreement with experimental data for all the three types of nozzles. Hence this spray model can be utilized to predict the initial droplet size and velocity distributions in sprays, which can then be implemented as a front-end subroutine to the existing computer codes.

A non-reactive model system comprising a highly concentrated and unstable oil-in-water emulsion was used to investigate the retention of oil by the membrane in producing biodiesel with a membrane reactor. Critical flux was identified using the relationship between the permeate flux and transmembrane pressure along with the separation efficiency of the membrane. It was shown that separation efficiencies above 99.5% could be obtained at all operating conditions up to the critical flux. It was observed that the concentration of oil in all collected permeate samples using the oil-water system was below 0.2 wt% when operating at a flux below the critical flux. Studies to date have been limited to the characterization of low concentrated emulsions below 15 vol.%. The average oil droplet size in highly concentrated emulsions was measured as 3200 nm employing direct light scattering (DLS) measurement methods. It was observed that the estimated cake layer thickness of 20 to 80 mm was larger than external diameter of the membrane tube i.e. 6 mm based on a large particle size. Settling of the concentrated emulsion permitted the detection of a smaller particle size distribution (30-100 nm) within the larger particles averaging 3200 nm. It was identified that DLS methods could not efficiently give the droplet size distribution of the oil in the emulsion since large particles interfered with the detection of smaller particles. The content of the smaller particles represented 1% of the total weight of oil at 30°C and 5% at 70°C. This was too low to be detected using DLS measurements but was sufficient to affect ultrafiltration. In order to study the critical flux in the presence of transesterification reaction and the effect of cross flow velocity on separation, various oils were transesterified in another membrane reactor providing higher cross flow velocity. higher cross flow velocity provides better separation by reducing materials deposition on the surface of the membrane due to higher shearing. The oils tested were canola, corn, sunflower and unrefined soy oils (Free Fatty Acids (FFA< 1%)), and waste cooking oil (FFA= 9%). The quality of all biodiesel samples was studied in terms of glycerine, mono-glyceride, di-glyceride and tri-glyceride concentrations. The composition of all biodiesel samples were in the range required by ASTM D6751 and EN 14214 standards. A critical flux based on operating pressure in the reactor was reached for waste cooking and pre-treated corn oils. It was identified that the reaction residence time in the reactor was an extremely important design parameter affecting the operating pressure in the reactor.
Natural Sciences and Engineering Research Council of Canada (NSERC)

For chemigation of nonsoluble pesticides, small oil-pesticides droplets (dmax tend to wash-off from foliage while large droplets tend to stick. Large droplets (dmax are buoyant, tend to rise in the irrigation pipeline and exit at the beginning of the pipeline; thus, uniformity and efficacy are poor. For this research, a new chemigation system was proposed. The system removes water from the irrigation pipeline, injects the oil-pesticide into the water stream, increases dispersion velocity in successively smaller tubing diameters, and finally injects the dispersion back into the irrigation pipeline. The higher velocity flow with high turbulent shear forces breaks the oil-pesticide into desired size droplets. Droplet break-up research was reviewed, and a model developed to predict maximum droplet size and size distribution. A maximum relative error of 40% was observed when dmax predicted by the model was compared against literature data. Equations to predict friction factor in helically coiled pipes and effective viscosity of oil-in-water dispersions were evaluated. The friction factor predicted by the Ito equation was in good agreement with the experimental data. Effective viscosity of soybean oil- and kerosene-in-water dispersions was predicted satisfactorily by the Richardson equation with k₄ = 2.5. Finally, center pivot field experiments were conducted using the new and conventional chemigation systems. For the conventional system, the soybean oil uniformity coefficient along the lateral was 61%, and oil applied over the last tenth of irrigated area was 9% of the initial concentration. For the new system, the uniformity coefficient was 73% and 98% for dmax of 875 mum and 98 mum, respectively; oil applied over the last tenth of the area was 27% and 90% of the initial concentration. Field data were compared with those predicted from a pipeline transport model for nonsoluble pesticides. Agreement between the model and the field data was excellent for both experiments using the new chemigation system. Based on the field results and simulation analyses, droplets < 150 μm should be desirable to keep the discharge uniformity coefficient over 97%, for 0.92 ≤ ρ(d)/ρ(c) ≤ 1.04.

Thesis (Ph.D)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.
Committee Chair: Athanasios Nenes; Committee Member: Andrew G. Stack; Committee Member: Irina N. Sokolik; Committee Member: Judith A. Curry; Committee Member: Mike Bergin; Committee Member: Rodney J. Weber. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This study explores an innovative approach to control the droplet size distribution produced by an electrospray with the intention of eventually being able to deliver precisely controlled quantities of precursor materials for nanofabrication. The technique uses a thermionic cathode to charge the droplets in excess of the Rayleigh limit, leading to droplet breakup or fission. The objective of these experiments was to assess whether the proposed technique could be used to produce a new droplet size distribution with a smaller mean droplet diameter without excessively broadening the distribution. An electrospray was produced in a vacuum chamber using a dilute mixture of ionic liquid. During their transit from the capillary source to a diagnostic instrument, the resulting droplets were exposed to an electron stream with controlled flux and kinetic energy. The droplets were sampled in an inductive charge detector to characterize changes in the size distribution. A positively biased anode electrode was used to collect electron current during droplet exposure. This collected current was used as the primary control variable and used as a measure of the electron flux. The anode bias voltage was a secondary control variable and used as a measure of the electron energy. In a series of seven tests, two sets showed evidence of fission having occurred resulting in the formation of two droplet populations after electron bombardment. Three sets of results showed evidence of a single droplet population after electron bombardment, but shifted to a smaller mean diameter, and one set of results was inconclusive. Because of the large standard deviation in the droplet diameter distributions, the two cases in which a second population was evident were the strongest indication that droplet fission had occurred.

A method using Pulsed Field Gradient Nuclear Magnetic Resonance PFG-NMR for water-incrude oil emulsion droplet size determination has been optimized and compared with optical microscope for validation. The method applies a combination of Pulsed-Field Gradient (PFG) NMR, Stimulated Echo (STE), and Carr-Purcell-Meimboom-Gill (CPMG) sequences for measuring diffusion, resolving oil and water signal and for measuring the attenuation due to a distribution in T2 values. This returns the droplet size distributions of water-in-oil emulsions within a minute. No prior assumption is made on the shape of the droplet size distribution, which enables the method to resolve for instance bimodal distributions. To validate this method, three different crude oils were used in the experiment. The emulsions prepared had water cuts from 10 to 40 %. The correlation between PFG-NMR and optical microscopy was good for the emulsions. Any potential discrepancies between the two techniques are discussed, so are the limitations and advantages of the methods.

A method using Pulsed Field Gradient Nuclear Magnetic Resonance PFG-NMR for water-incrude oil emulsion droplet size determination has been optimized and compared with optical microscope for validation. The method applies a combination of Pulsed-Field Gradient (PFG) NMR, Stimulated Echo (STE), and Carr-Purcell-Meimboom-Gill (CPMG) sequences for measuring diffusion, resolving oil and water signal and for measuring the attenuation due to a distribution in T2 values. This returns the droplet size distributions of water-in-oil emulsions within a minute. No prior assumption is made on the shape of the droplet size distribution, which enables the method to resolve for instance bimodal distributions. To validate this method, three different crude oils were used in the experiment. The emulsions prepared had water cuts from 10 to 40 %. The correlation between PFG-NMR and optical microscopy was good for the emulsions. Any potential discrepancies between the two techniques are discussed, so are the limitations and advantages of the methods.

This work detailed the physical and chemical characterization of oil water mixtures prepared using fresh and weathered Macondo related oils under different conditions of mixing energy/time and in the presence/absence of chemical dispersants. The results indicated that WAFs produced consistent, droplet free solutions for both source and weathered oils with concentration ranges that represented the soluble components of the oil used. Chemically enhanced WAFs prepared with the source oil generated a large amount of micron-size droplets; however the viscosity of the weathered oils were a limiting factor for the preparation of CEWAFs with weathered oils. Droplet size distributions were influenced by the amount of energy in the system and the oil weathering stage, when high energy WAFs were made the increase in weathering of the oil resulted in the formation of smaller droplets that were more stable over time.

Class of 2015 Abstract
Objectives: To evaluate the in vitro performance of various pressurized metered dose inhaler (pMDI) formulations by cascade impaction primarily focusing on throat deposition, fine particle fraction (FPF), and mass-median aerodynamic diameter (MMADR) measurements Methods: Ten solution pMDIs were prepared with varying cosolvent species in either low (8% w/w) or high (20% w/w) concentration. The chosen cosolvents were either alcohol (ethanol, n-propanol) or acetate (methyl-, ethyl-, and butyl acetate) in chemical nature. All formulations used HFA-134a propellant and 0.3% drug. The pMDIs were tested by cascade impaction with three different inlets to determine the aerodynamic particle size distribution (APSD), throat deposition, and FPF of each formulation. Theoretical droplet evaporation time (DET), a measure of volatility, for each formulation was calculated using the MMADR. Results: Highly volatile formulations with short DET showed consistently lower throat deposition and higher FPF than their lower volatility counterparts when using volume-constrained inlets. However, FPF values were not significantly different for pMDI testing with a non-constrained inlet. The MMADR values generated with volume-constrained inlets did not show any discernible trends, but MMADR values from the non-constrained inlet correlated with DET. Conclusions: Formulations with shorter DET exhibit lower throat deposition and higher FPF, indicating potentially better inhalational performance over formulations with longer DET. There appear to be predictable trends relating both throat deposition and FPF to DET. The shift in MMADR values for volume-constrained inlets suggests that large diameter drug particles are preferentially collected in these inlets.

[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

Monitoring of emulsion properties is important in many applications, like in foods and pharmaceutical products, or in emulsion polymerization processes, since aged and broken emulsions perform worse and may affect product quality. In machining processes, special types of emulsions called metalworking fluids (MWF) are widely used, because of its combined characteristics of cooling and lubrication, increasing the productivity, enabling the use of higher cutting speeds, decreasing the amount of power consumed and increasing tool life. Even though emulsion quality monitoring is a key issue in manufacturing processes, traditional methods are far from accurate and generally fail in providing the tools for determining the optimal useful life of these emulsions, with high impact in costs. The present study is dedicated to the application of a spectroscopic sensor to monitor MWF emulsion destabilization, which is related to changes in its droplet size distribution. Rapeseed oil emulsions, artificially aged MWF and MWF in machining application were evaluated, using optical measurements and multivariate calibration by neural networks, for developing a new method for emulsion destabilization monitoring. The technique has shown good accuracy in rebuilding the droplet size distribution of emulsions for monomodal and bimodal distributions and different proportions of each droplet population, from the spectroscopic measurements, indicating the viability of this method for monitoring such emulsions. This study is part of a joint project between the University of São Paulo and the University of Bremen, within the BRAGECRIM program (Brazilian German Cooperative Research Initiative in Manufacturing) and is financially supported by FAPESP, CAPES, FINEP and CNPq (Brazil), and DFG (Germany).
Sem resumo em português.

O desenvolvimento de algoritmos computacionais para a obtenção de distribuições de tamanho de partícula em dispersões e que utilizam dados espectroscópicos em tempo real e in-line a partir de sensores permitirá uma variedade de aplicações, como o monitoramento de propriedades em fluidos de corte industriais, acompanhamento de processos de polimerização, tratamento de efluentes e sensoriamento atmosférico. O presente estudo tem como objetivo a implementação e comparação de técnicas para resolução de problemas de inversão, desenvolvendo algoritmos que forneçam distribuição de tamanho de partículas em dispersões a partir de dados de espectroscopia UV-Vis-Nir (Ultravioleta, Visível e Infravermelho próximo). Foram implementadas quatro técnicas, sendo uma delas um método alternativo sem a presença de etapas de inversão. Os métodos que utilizaram alguma técnica de inversão evidenciaram a dificuldade em se obter distribuições de tamanho de gotas (DTG) de boa qualidade, enquanto o método alternativo foi aquele que se mostrou mais eficiente e confiável. Este estudo é parte de um programa cooperativo entre a Universidade de São Paulo e a Universidade de Bremen chamado programa BRAGECRIM (Brazilian German Cooperative Research Initiative in Manufacturing) e é financiado pela FAPESP, CAPES, FINEP e CNPq (Brasil) e DFG (Alemanha).
The development of computer algorithms to obtain the particle size distributions in dispersions using spectroscopic data in real time and in-line from sensors enable a variety of applications such as monitoring properties in industrial cutting fluids, monitoring of polymerization processes, wastewater, atmospheric sensing and other applications. The aim of this study is to implement techniques for inversion problem solving, by testing algorithms that provide particle size distribution in dispersions from UV-Vis-Nir (Ultraviolet, Visible and Near-Infrared) spectroscopic data. Four techniques have been implemented, one of them being an alternative method without the inversion step. The methods using inversion techniques showed difficulties to obtain droplet size distributions (DSD) with good quality, while the alternative method was the one that was more efficient and reliable. This study is part of a cooperative program between the University of São Paulo and the University of Bremen, within the BRAGECRIM program (Brazilian German Cooperative Research Initiative in Manufacturing) and is financially supported by FAPESP, CAPES, FINEP and CNPq (Brazil) and DFG (Germany).

O monitoramento de emulsões utilizadas na indústria metalmecânica compõe uma importante atividade para o controle da qualidade das peças trabalhadas, proporcionando também o aumento da vida útil de ferramentas e maquinários utilizados neste setor através da lubrificação e refrigeração da região de corte. Em grande parte dos casos, estas emulsões são preparadas pela diluição de um fluido de corte em meio aquoso, constituindo assim um conjunto de gotículas estabilizadas em um meio contínuo devido à presença de compostos emulsificantes, estando constantemente sujeitas a ciclos de aquecimento e resfriamento durante os processos de usinagem. Apesar do acompanhamento deste material ser realizado através de análises periódicas usuais, não há um método eficiente estabelecido para verificar sua qualidade em tempo real e em linha de processo. Neste contexto, torna-se possível aplicar técnicas relacionadas à espectroscopia UV-Vis para se obterem informações sobre a estabilidade destes sistemas, correlacionando intensidades de espalhamento de luz com as dimensões das gotas presentes no meio. Dessa forma, tornou-se possível o estudo da desestabilização térmica de emulsões de um fluido de corte comercial, a qual mostrou-se, através do acompanhamento do cálculo do expoente do comprimento de onda, dependente do tempo de exposição ao aquecimento e de sua temperatura média temporal, não sendo influenciada pela perda de meio contínuo por processos evaporativos ou sua posterior reposição. Também se verificou que parâmetros típicos do processo de preparo de emulsões, como a temperatura do meio dispersante e o tempo de repouso do fluido de corte sobre a superfície do mesmo, apresentam fundamental importância para a definição do tamanho médio de gota inicial destes sistemas, o que forneceu evidência da possibilidade de se relacionar a área sob espectros de extinção de luz com tamanhos médios de gota.
The monitoring of emulsions used in the metal-mechanical industry comprise an important activity to the quality control of the products manufectured, also providing an increase in the working life of the tools and machinery employed in this sector through the lubrication and refrigeration of the cutting zone. In the majority of cases, these emulsions are prepared diluting a metalworking fluid in an aqueous media, constituting a collection of particles stabilized by emulsifiers and undergoing heating and cooling cycles during metalworking processes. Currently, monitoring routines are based on regular analyses of samples taken from the process fluid, and an effective in-line method is not available to monitor emulsion quality in real time. In this context, it is possible to apply techniques related to UV-Vis spectrocopy in order to obtain information concerning the stability of those systems, correlating light scattering intensities to the droplet dimensions. In this study, it was possible to investigate the thermal destabilisation of a commercial metalworking fluid emulsion, which showed, through the evaluation of the wavelength exponent, to be dependant on the exposure time to heating and its time-averaged temperature. It was also noted that the loss of continuous phase by evaporation and its reposition do not affect the emulsion stability. Moreover, it was observed that important emulsion preparation parameters, such as continuous phase temperature and the time span between the addition of the metalworking fluid on the water surface and the stirring, have fundamental roles in defining the initial average droplet size, which made possible to correlate the area under the light extinction spectra with average droplet sizes.

As emulsões inversas água/óleo são sistemas multifásicos complexos, constituídos por uma fase líquida aquosa dispersa numa fase lipídica (contínua), e cristais de gordura para estabilizar a fase dispersa. O mimetismo lipídico nestas emulsões advém da estabilização através do controlo da cinética da cristalização das gorduras. A natureza e a morfologia das fases formadas estão correlacionadas com as propriedades mecânicas e reológicas destes sistemas. Foram estudadas cinco emulsões inversas água/óleo com diferentes formulações, em duas séries diferentes (2011 e 2013), utilizando diferentes técnicas experimentais, a saber: espectrometria mecânica (ensaios reológicos), microscopia óptica (observação estática e em escoamento torcional), instrumental (cor e textura) e avaliação sensorial. Os ensaios reológicos incluíram ensaios em regime transitório (relaxação de tensões e arranque de escoamento), ensaios em regime dinâmico (determinação do módulo de distorção complexo) e ensaios em regime permanente (escoamento entre pratos paralelos e escoamento Couette), para determinação experimental das funções materiais das emulsões associadas a cada um dos ensaios referidos. A microstrutura e a composição, o tamanho de gota e a distribuição de tamanhos de gota das emulsões inversas foram analisadas e medidas por microscopia óptica e análise de imagem. A visualização de escoamentos e da resposta a diferentes deformações foi efectuada utilizando uma célula óptica de torção acoplada a um microscópio óptico e a uma câmara digital para observação em tempo real das alterações de textura causadas por deformações ou velocidades de deformação (escoamentos). Foi também efectuada avaliação sensorial e instrumental (cor e textura) das diferentes composições das emulsões inversas. A interpretação dos resultados experimentais dos ensaios reológicos foi feita com base no modelo de Palierne, considerando um modelo da emulsão inversa constituída por uma fase lipídica contínua, modificada pela presença da rede de cristais lipídicos, e dois tipos de inclusões da fase aquosa: inclusões “mais flexíveis” com uma interface lípidoágua sem cristais lipídicos, e inclusões “menos flexíveis” onde a interface é modificada pela rede de cristais lipídicos. O ajuste efectuado às funções materiais reológicas mostrou que o modelo utilizado consegue descrever, com boa aproximação, os resultados experimentais obtidos. A caracterização reológica da resposta da emulsão a diferentes histórias da deformação (degrau de deformação, deformação sinusoidal, arranque de escoamento e escoamento permanente) foram complementadas com a observação em tempo real, através de uma câmara digital, das alterações de textura ocorridas em cada um dos ensaios referidos. Foi feita uma avaliação sensorial das diferentes formulações de emulsões inversas consideradas, utilizando um painel de provadores treinado. Através da análise de componentes principais, verificou-se que a avaliação sensorial e a avaliação instrumental são correlacionáveis, e que essas correlações podem ser analisadas em termos das constantes materiais reológicas medidas experimentalmente; Rheological and microstructural characterization of water-and-oil food emulsions ABSTRACT: The water-in-oil (w/o) food emulsions are complex multiphase systems, consisting of a liquid aqueous phase dispersed in a liquid continuous lipid phase and fat crystals to stabilize the dispersed phase. The mimicry of these lipid emulsions stabilization arises by controlling the kinetics of crystallization of fat. The nature and morphology of the phases formed are correlated with rheological and mechanical properties of these systems. Five water/oil emulsions with different formulations were studied on two different series (2011 and 2013), using various experimental techniques, such as: mechanical spectrometry (rheological tests); optical microscopy (torsional static and flow observation); instrumental (colour and texture) and sensory evaluation. The rheological measurements performed assays at transient regime (stress relaxation and start flow), assays at dynamic regime (determination of the complex shear modulus) and assays in steady state (flow between parallel plates and Couette flow), for experimental determination of material functions associated with each of these tests. The microstructure and composition, droplet size and droplet size distribution of w/o emulsions were analyzed and measured by optical microscopy and image analysis. The visualization of flow and response to different strains was performed using an optical shear cell coupled to an optical microscope and a digital camera for real-time observation of texture changes caused by deformation or strain rates (flows). Was also carried out sensory and instrumental evaluation (colour and texture) of different compositions of inverse emulsions. The understanding of the experimental results of the rheological measurements was established on Palierne model considering a inverse emulsion model comprising a continuous lipid phase, modified by the presence of crystals lipid network, and two kinds of aqueous phase enclosures: enclosure "more flexible "with a lipid-water interface without lipid crystals, and enclosure "less flexible" where the interface is modified by the lipid crystal network. The adjustment of rheological material functions showed that the model used can describe the experimental results with close approach. The rheological characterization of the emulsion response to different deformation history (strain step, sinusoidal deformation, start flow and continuous flow) were complemented with the observation of texture changes occurring in each of the tests in real time using a digital camera. Was performed a sensory evaluation of inverse emulsions different formulations using a trained taste panel. It was found by means of principal component analysis that the sensory and instrumental evaluation are correlated, and these correlations can be analysed in terms of rheological material constants experimentally measured.

碩士
國立臺灣大學
環境工程學研究所
92
Droplet exhaled from human may carry microorganisms capable of transmitting disease in short and long distances. The size of droplet will mainly influence the transmission mode of such infectious droplet. The aim of this study was to establish the size distribution of droplet and droplet nuclei exhaled by healthy individuals, and using sample bag and column to collect them. The droplets from human subjects performing coughing were measured by aerodynamic particle sizer (APS) and scanning mobility particle sizer (SMPS) system, and establish the droplet size distribution. Computing the evaporation time, falling distances, horizontal traveling distances with some assumptions. Furthermore, the data was treated with statistical analysis, comparing the difference of different ages and sexual classification. The data of APS monitoring showed the respiratory droplets ranged from 0.5 to 20 mm and 90~95% of droplets were between 2 and 10 mm. The mode of droplet size distribution is between 5 and 7 mm. Most droplets were less than 10 mm. The diameter of droplet nuclei was found to range in diameter from 0.5 to 5 mm, and the most amount was between 0.6 to 2 mm. The droplets size were not significantly difference in age and sexual classification. The SMPS confirmed the existence of droplets ranged from 0.02 to 0.5 mm. In the environment of 20℃ and 50% relative humidity, it took only 0.04 seconds for 5 mm droplet to evaporate, and the falling distance was less than 0.002 cm, the horizontal traveling distance was about 0.008 cm. It showed the range of droplets produced by coughing was near the source, and evaporating to form droplet nuclei quickly. Droplet nuclei could suspend in the environment for a long time, and transport with air current. The microorganisms may transmit disease by air. Besides, if droplet or droplet nuclei fall on the surface of objects, one may be infected by toughing the infectious objects.

碩士
國立臺灣大學
環境工程學研究所
93
Droplet exhaled from human may carry microorganisms capable of transmitting disease. As a result of the size be smaller than micron scale had been proven to occupy the great part of size distribution . The goal of this study was to establish the nano scale size of droplet exhaled by healthy individuals, and to compare the sexual differences of the coughing velocity and droplet concentration. Using sample bag to collect droplet. The droplets from human subjects performing coughing were measured by scanning mobility particle sizer (SMPS) system, and establish the droplet size distribution. Furthermore, these data were treated with statistical analysis, comparing the difference of different ages and sexual classification. Then computing the evaporation time, falling distances, horizontal traveling distances with some assumptions. The data of SMPS system showed the respiratory droplets ranged from 0.019 to 0.35 mm and 80% of droplets were between 0.03 and 0.2 mm. Most droplets were more than 0.03 mm. The droplets size were not remarkably difference in age and sexual classification, except for group 2 in sexual classification. The data of wind meter showed the velocity ranged from 0.13 to 1.88 m/s. In this study we found the droplet concentration will increase with coughing velocity. In the data of coughing velocity and droplet concentration, male’s is larger than female’s. In the environment of 20℃ and 50% relative humidity, it took only 7.07×10-5 seconds for 0.2 mm droplet to evaporate, and the falling distance was less than 4.40×10-9 cm, the horizontal traveling distance was about 8.58×10-5 cm. It showed the range of droplets produced by coughing was near the source, and evaporating to form droplet nuclei quickly. If droplet nuclei transmit in the environment, there will be the possibility of infection of diseases. Many infectious diseases belong to nano scale size such as SARS. Therefore this study could be understood its distribution in the smaller scale of droplet size.

碩士
國立中山大學
機械與機電工程學系研究所
93
Water and R-134a sprays as they impinge on the flat endplate of a circle are studied experimentally. In order to optimize water and R-134a sprays cooling efficiency, a detailed characterization and understanding of the spray formation is essentially needed. The effects of the jet exit velocity and Weber number on spray segregation are investigated. An optical image system was used to quantify the droplet size and distribution. LDV measurements were used to characterize the local velocity and velocity fluctuation distribution from a commercial available nozzle in both axial and radial directions. It is found in the water spray that local mean droplet diameter (SMD) decreases as jet exit velocity increases and as jet proceeds further downstream as well. Furthermore, the SMD and radial velocity are found to be the largest at the outer edges of the water spray. In contrast, the radial velocity is found to be the smallest at the outer edges of the R-134a spray. The SMD and radial velocity continuously decrease across both the water spray and R-134a spray toward the jet axis; while the corresponding axial velocity is the maximum there. Moreover, the R-134a spray jet heat transfer in non-boiling regime was shown to be dependent on the velocity of the impinging jets in terms of Weber number and other related parameters which are in good agreement with those of previous studies.

碩士
國立臺北科技大學
能源與冷凍空調工程系
107
The fire-extinguishing system applying automatic discharge sprinklers for ceiling height above 10 meters has been studied. The focus is on the phenomenon about the effects of the water droplet size and the size distribution of the discharge sprinklers. The effects of discharge droplets on the smoke flow were also. A full-scale experiment was setup to observe the physical phenomena. A 3D modeling was further undertaken to simulate the fire, smoke exhaust, smoke flow and interaction of water droplets and smoke flow. This research applied FDS in the 3D simulation. This study adopted logarithmic normal / Rosin-Rammler distribution for the sprinkler’s droplet size. All the parameters considered include (1) droplet size distribution, and (2) medium droplet diameter. It has been found that the discharge water droplets would induce the downward flow of smoke and has adverse effect on the visibility of smoke. Smaller water droplet size would take longer time to extinguish the fire, specifically for medium size at 1000 μm. The smaller size water droplet would evaporate faster and has to overcome the buoyancy force of fire. At this droplet size, smoke visibility was lower. Three medium droplet size, 1000μm, 1300μm, and 2000μm were studied. With equal fire extinguishing performance 2000μm droplet had a higher smoke visibility. When the sprinklers are actuated quicker in early fire and with less smoke generation, better smoke visibility would be expected so to have better fire safety.