Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-10-06Bitstream added on 2014-06-13T18:31:03Z : No. of bitstreams: 1 irikura_si_me_ilha.pdf: 10628926 bytes, checksum: 6e06f10958376596936e2de7dd169f63 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Como se sabe dureza e resistência mecânica dependem da microestrutura do aço. Em aços multiestruturais é importante compreender a influência individual da estrutura do microconstituinte. O único ensaio prático que pode ser realizado individualmente no microconstituinte estrutural em aços multiestruturais é o ensaio de dureza com pequenas indentações sob cargas baixas ou ensaio de microdureza. Já que é possível obter a resistência ou a curva tensão-deformação da dureza de um aço mono estrutural, tal como ferrita, perlita, bainita ou martensita, também é possível estimar a resistência ou a curva tensão-deformação para aços multiestruturais conhecendo-se a fração volumétrica de cada constituinte estrutural individualmente presente. O trabalho tem como objetivo analisar o comportamento de microestruturas de um cordão-de-solda sob ensaio de microdureza com a tentativa de se recompor o valor de dureza Vickers (HV) obtido no ensaio de (macro) dureza, observando-se assim o comportamento individual dos constituintes. O material ensaiado foi a junta soldada por arco submerso do aço estrutural COS Civil 300. Tratamentos térmicos foram realizados para que se pudessem obter microestruturas variadas. As amostras foram analisadas metalograficamente e também por anális... / It is well known that both hardness and strength depend on the microstructure of steels. In multistructure steels, it is important to understand the influence of individual structure microconstituent. The only practical test that can be performed on the individual microstrutural constituents in multistructure steels is a hardness test with a small indentation under low load or microhardness test. If is possible to obtain strength or the stress-strain curves from the hardness of single structure steels, such as ferrite, perlite, bainite or martensite, it is may possible to estimate the strengths or stress-strain curves of multistructure steels by knowing the volume fraction of the individual structural constituents present. The purpose of the present work is analyzing the microstrutural behaviour of weld joint under microhardness test with the attempt of recomposing the Hardness Vickers (HV) value obtained on the (macro) hardness test, observing then the individual behaviour of the constituents. The material tested was the joint welded by submerge- arc welding of the structural steels COS Civil 300. Heat treatment had been carried out to obtain different microstrutures. The specimens were analyzed by metallography and quantitative analysis... (Complete abstract click electronic access below)

Orientador: Ruís Camargo Tokimatsu / Banca: Cecília A. de C. Zavaglia / Banca: Vicente Afonso Ventrella / Resumo: Como se sabe dureza e resistência mecânica dependem da microestrutura do aço. Em aços multiestruturais é importante compreender a influência individual da estrutura do microconstituinte. O único ensaio prático que pode ser realizado individualmente no microconstituinte estrutural em aços multiestruturais é o ensaio de dureza com pequenas indentações sob cargas baixas ou ensaio de microdureza. Já que é possível obter a resistência ou a curva tensão-deformação da dureza de um aço mono estrutural, tal como ferrita, perlita, bainita ou martensita, também é possível estimar a resistência ou a curva tensão-deformação para aços multiestruturais conhecendo-se a fração volumétrica de cada constituinte estrutural individualmente presente. O trabalho tem como objetivo analisar o comportamento de microestruturas de um cordão-de-solda sob ensaio de microdureza com a tentativa de se recompor o valor de dureza Vickers (HV) obtido no ensaio de (macro) dureza, observando-se assim o comportamento individual dos constituintes. O material ensaiado foi a junta soldada por arco submerso do aço estrutural COS Civil 300. Tratamentos térmicos foram realizados para que se pudessem obter microestruturas variadas. As amostras foram analisadas metalograficamente e também por anális... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: It is well known that both hardness and strength depend on the microstructure of steels. In multistructure steels, it is important to understand the influence of individual structure microconstituent. The only practical test that can be performed on the individual microstrutural constituents in multistructure steels is a hardness test with a small indentation under low load or microhardness test. If is possible to obtain strength or the stress-strain curves from the hardness of single structure steels, such as ferrite, perlite, bainite or martensite, it is may possible to estimate the strengths or stress-strain curves of multistructure steels by knowing the volume fraction of the individual structural constituents present. The purpose of the present work is analyzing the microstrutural behaviour of weld joint under microhardness test with the attempt of recomposing the Hardness Vickers (HV) value obtained on the (macro) hardness test, observing then the individual behaviour of the constituents. The material tested was the joint welded by submerge- arc welding of the structural steels COS Civil 300. Heat treatment had been carried out to obtain different microstrutures. The specimens were analyzed by metallography and quantitative analysis... (Complete abstract click electronic access below) / Mestre

The thermophysical properties of nanofluids have attracted the attention of researchers to a far greater extent than the heat transfer characteristics of nanofluids have. Contradictory results on the thermal-fluid behaviour of nanofluids have been numerically and experimentally reported on in the open literature. Natural convection has not been investigated experimentally as much as the other properties of nanofluids. In this study, the characteristics and stability of Al2O3-water nanofluids (d = 20 30 nm) were analysed using a Malvern zetasizer, zeta potential and UV-visible spectroscopy. The natural convection of Al2O3- water nanofluids (formulated with a single-step method) was experimentally studied in detail for the volume fractions 0, 0.05, 0.1, 0.2, 0.4 and 0.6% in a rectangular cavity with an aspect ratio of 1, heated differentially on two opposite vertical walls for the Rayleigh number (Ra) range 3.49 x 10⁸ to 1.05 x 10⁹. The viscosity of Al2O3-water nanofluids measured between 15 and 50 °C. The effect of temperature and volume fraction on viscosity was also investigated. A detailed study of the nanoparticle concentration effect on the natural convection heat transfer coefficient was performed. It was found that increasing the concentration of nanoparticles improves the heat transfer coefficient by up to 15% at a 0.1% volume fraction. Further increasing the concentration of nanoparticles causes the natural convection heat transfer coefficient to deteriorate. This research also supports the idea that "for nanofluids with thermal conductivity more than the base fluids an optimum concentration may exist that maximises heat transfer in an exact condition as natural convection, laminar force convection or turbulence force convection". / Dissertation (MEng)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

This Master of Engineering investigation focuses on the natural convection of nanofluids in rectangular cavities. The governing equations applied to analyse the heat transfer and fluid flow occurring within the cavity are given and discussed. Special attention is given to the models that were developed to predict the thermal conductivity and dynamic viscosity of such nanofluids. A review concerning past investigations into the field of natural convection of nanofluids in cavities is made. The investigation is divided into experimental works and computational fluid dynamics (CFD) numerical investigations. Through the literature review, it was discovered that many numerical models exist for the prediction of the thermophysical properties of nanofluids, specifically thermal conductivity and viscosity. Depending on the nanofluid and the application, different models can be used. The literature study also revealed that most previous works were done in the CFD field. Very few experimental studies have been performed. Numerical CFD investigations, however, need experimental results for validation purposes, leading to the conclusion that more experimental work is needed. The heat transfer capability and thermophysical properties of the nanofluid are investigated based on models found in literature. The investigation incudes measuring the heat transfer inside a cavity filled with a nanofluid and subjected to a temperature gradient. The experiment is performed for several volume fractions of particles. An optimum volume fraction of 0.005 is obtained. At this volume fraction the heat transfer enhancement reaches a maximum for the present investigation. The investigation is repeated as a numerical investigation using the commercially available CFD software ANSYS-FLUENT. The same case as used in the experimental investigation is modelled as a two-dimensional case and the results are compared. The same optimum volume fraction and maximum heat transfer is obtained with an insignificantly small difference between the two methods of investigation. This error can be attributed to the minor heat losses experienced from the experimental setup as in the CFD adiabatic walls considered. It is concluded that, through the inclusion of TiO2 particles in the base fluid (deionised water), the thermophysical properties and the heat transfer capability of the fluid are altered. For a volume fraction of 0.005 and heat transfer at a temperature difference of 50 °C, the heat transferred through the fluid in the cavity is increased by more than 8%. From the results, it is recommended that the investigation is repeated with TiO2 particles of a different size to determine the dependency of the heat transfer increase on the particle size. Various materials should also be tested to determine the effect that material type has on the heat transfer increase. / Dissertation (MEng)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Yes / This work aims to present an improved version of the liquid mixture identification sensor, the proposed sensor is tested experimentaly on mixture of water ethanol, the identification of liquid is based on the measurement of frequency displacement, and comparison with reference values of water ethanol. This device is based on metamaterial structure which is a CRLH (composite right left hand) resonator with ZOR (Zero Order Resonator). The CRLH in addition to its property of miniaturization effect, when combined with ZOR, the resonant frequency of various volume fraction are extended, which make the sensitivity higher. The high sensitivity of the sensor is obtained by an optimum choice of the CRLH components. The geometrical size of the sensor is 20 mm by 11 mm. It was printed on a RT/Duroid 5880 substrate with a very short testing surface area of 4 mm by 8 mm, the liquid is placed on the top side of the sensor, exactly on the CRLH structure. Three prototypes of sensors operating from 1 GHz to 3 GHz are proposed, designed and simulated using the commercial software HFSS (high-frequency structural simulator). The main advantages of this work is first miaturization effect, second high sensitivity and finaly a wide range of liquid can be tested with this sensor. To prove the working principle, ethanol with different volume fractions was adopted as a liquid under test, the obtained results present very good agreement with the literature and suggested that it is a miniaturised and high sensitive candidate (better than 1.38%) for liquid mixture identification.

It has been historically assumed that most of the uncertainty associated with the aerosol indirect effect on climate can be attributed to the unpredictability of updrafts. We assess the sensitivity of cloud droplet number density to realistic variations in aerosol chemical properties and to variable updraft velocities using a 1-dimensional cloud parcel model. The results suggest that aerosol chemical variability may be as important to the aerosol indirect effect as the effect of unresolved cloud dynamics, especially in polluted environments. We next used a continuous flow streamwise thermal gradient Cloud Condesnation Nuclei counter (CCNc) to study the water-uptake properties of the ambient aerosol, by exposing an aerosol sample to a controlled water vapor supersaturation and counting the resulting number of droplets. The heat transfer properties and droplet growth within the CCNc were first modeled and experimentally characterized. We describe results from the MIRAGE field campaign at a ground-based site during March, 2006. Size-resolved CCN activation spectra and hygroscopic growth factor distributions of the ambient aerosol in Mexico City were obtained, and an analytical technique was developed to quantify a probability distribution of solute volume fractions for the CCN, as well as the aerosol mixing-state. The CCN were shown to be much less CCN active than ammonium sulfate, with water uptake properties more consistent with low molecular weight organic compounds. We also describe results from the GoMACCS field study, an airborne field campaign in Houston, Texas during August-September, 2006. GoMACCS tested our ability to predict CCN for highly polluted conditions with limited chemical information. Assuming the particles were composed purely of ammonium sulfate, CCN closure was obtained with a 10% overprediction bias on average for CCN concentrations ranging from less than 100 cm-3 to over 10,000 cm-3, but with on average 50% variability. Assuming measured concentrations of organics to be internally mixed and insoluble tended to reduce the overprediction bias for less polluted conditions, but led to underprediction bias in the most polluted conditions. Comparing the two campaigns, it is clear that the chemistry of the particles plays an important role in our ability to predict CCN concentrations.

Les milieux granulaires présentent une grande diversité de comportements physiques que l'on peut relier aux différents états "conventionnels" de la matière : solide, liquide ou gaz. Les travaux décrits dans ce manuscrit se concentrent sur les écoulements granulaires denses présentant de nombreuses analogies avec les liquides moléculaires. Les expériences présentées dans ce manuscrit sont réalisées en utilisant des jets granulaires s'écoulant d'un réservoir, dans l'air et sous l'effet de la gravité. Quelques propriétés de tels jets sont étudiées, notamment l'évolution du diamètre au cours de la propagation. L'évolution de cette grandeur permet une description des jets granulaires comme des fluides incompressibles dans une certaine gamme de diamètres de sortie D et de diamètres des particules d, résumés en une grandeur réduite : le rapport d'aspect D/d. Lorsque ce dernier est inférieur à une grandeur critique proche de 15, les jets granulaires cessent de se comporter comme des liquides incompressibles et sont alors décrits comme des gaz en expansion.La transition entre les deux régimes d'écoulements est expliquée par un modèle faisant intervenir l'équilibre entre la température granulaire et sa dissipation par l'inélasticité des collisions entre les billes constituant le milieu granulaire. En utilisant les mesures de la température granulaire accessibles à la paroi dans le réservoir, ce modèle permet d'obtenir les profils de température et de fraction volumique du milieu en fonction du rapport d'aspect ainsi que leurs valeurs moyennes, présentant un bon accord avec les mesures de la fraction volumique en sortie du réservoir.Dans le régime "liquide" des jets granulaires mis en évidence ici, une tension de surface effective est mesurée par l'étude d'une instabilité similaire à celle de Rayleigh-Plateau. En soumettant le jet à une oscillation verticale apparaît une modulation du diamètre du jet dont il est possible d'étudier l'évolution au cours du temps. La mesure des taux de croissance des modes instables excités permet d'établir la relation de dispersion et d'obtenir une tension de surface effective dans les jets granulaires. Il est montré que cette tension de surface effective décroit lorsque la taille des particules augmente, décroit lorsque la pression de l'air ambiant diminue et augmente avec la distance de propagation.Le mécanisme proposé pour expliquer l'origine de cette tension de surface effective est l'interaction entre le jet granulaire et l'air ambiant. Les profils de vitesse de l'air entraîné par le jet sont mesurés pour différentes diamètres de particules, différentes pression ambiantes et différentes distances de propagation. L'entraînement de l'air et les profils de vitesses sont utilisés pour définir certaines forces s'exerçant sur les billes et construire une tension de surface effective : l'ordre de grandeur de cette tension de surface est incompatible avec les mesures réalisées précédemment. Une mesure de la pression de l'air à l'intérieur du jet granulaire permet d'obtenir une force exercée par la perméation de l'air à travers les pores du jet dont l'ordre de grandeur est correct. / Granular media exhibit a broad range of behaviours that can be related to the common states of matter: solid, liquid and gaseous. The experiments described in this thesis focus on dense granular flows ad their analogies with molecular liquid flows.The work presented focuses on granular material flowing from a reservoir, in ambient air under the effect of gravity. Some properties of such jets are presented, among them the evolution of the diameter of the jet along propagation. This evolution allows one to describe granular jets as incompressible liquid jets for a certain range of parameters D (exit diameter) and d (beads diameter). When using a reduced variable D/d (the aspect ratio), a transition appears close to a critical value (approx. 15) below which the granular jet exhibit a gas-like behaviour.This transition is explained using a model supposing balance between the heat flux (from the granular temperature imposed at the wall of the reservoir) and its dissipation through inelastic collisions between the beads in the granular medium. This model allows one to compute the temperature and volume fraction profiles as well as their mean values which are in good agreement with the experimental measurements (volume fraction at the exit).In the "liquid" regime defined previously, an effective surface tension is measured by studying the unstable modes of a Rayleigh-Plateau like instability. This instability is obtained by imposing a vertical oscillation on the jet which induces a diametrical modulation whose evolution is measured. Measurements of the growth rates of these unstable modes leads to the dispersion relation $\omega (kr_{0})$ and to an effective granular surface tension. This surface tension shows a diminution when the beads' size increases, a diminution when the air pressure is reduced and a growth along propagation.The proposed mechanism explaining this effective surface tension is the interaction between the granular jet and the surrounding air. Air velocity profiles are measured for different beads diameters, different air pressures and different distances below the outlet. Using these velocity profiles, various forces exerted on the beads are calculated, leading to a surface tension whose order of magnitude is lower than the one measured through the Rayleigh-Plateau instability. The right order of magnitude can be obtained by considering the air permeation through the pores on the surface the jet and the force exerted along the surface of said pores.

Sérios problemas ambientais têm origem em processos de combustão incompletos. Entre os produtos indesejados está a fuligem, considerada como um dos principais fatores da mudança climática observada nos último anos. Desta forma, ferramentas para diagnóstico da emissão de material particulado se fazem necessárias. Com o advento do laser, o desenvolvimento de técnicas óticas não intrusivas teve início. Dentre elas, destaca-se a técnica denominada incandescência induzida por laser (laser induced incandescence – LII), a qual pode gerar resultados resolvidos no espaço para a fração volumétrica de fuligem. Neste contexto, este trabalho apresenta um estudo experimental sobre a produção de fuligem em duas situações: na primeira, foram estudadas chamas laminares pré-misturadas de etileno e ar aplicando-se a técnica LII. Os resultados foram calibrados a partir da fração volumétrica de fuligem média empregando a técnica de extinção de luz, obtendo-se, então, resultados quantitativos espacialmente resolvidos da fração volumétrica de fuligem. A utilização de diferentes gases no escoamento anular também foi avaliada. A segunda situação abordada envolve o estudo de chamas laminares não pré-misturadas utilizando o gás natural como combustível. O impacto da diluição de inertes em diferentes proporções sobre a fração volumétrica de fuligem em diversas alturas da chama foi estudado por meio da técnica LII. Os resultados obtidos foram comparados à outros resultados presentes na literatura e servirão como validação de futuros modelos de formação de fuligem. / Serious environmental problems are assigned to incomplete combustion processes. Among the unwanted products, soot can be related as an important factor of climate changes observed in the last years. Thus, particulate material emissions diagnostic tools are necessary. Due the laser advent, the development of non-intrusive optical techniques was possible. One of the most importante technique is the laser induced incandescence, LII, which can generate spatially and temporally resolved results of soot volume fraction. In this context, an experimental study regarding the soot production was developed in two different situations: in the first one, premixed laminar flames of ethylene and air were investigated by applying the LII technique. The results were calibrated through the average of soot volume fraction results obtained by the light extinction technique. Therefore, it was possible to obtain quantitative results of spatially resolved soot volume fraction. Different gases employment at the annular flow were also evaluated. The second situation studied involves the analysis of natural gas laminar non-premixed flames. The impact of different inert gas dilution ratio on the soot volume fraction at different heights of the flame was evaluated by the LII technique. The results were compared to other authors and will serve as validation for future soot formation models.

Several problems must be solved in the construction, design, and operation of a nuclear fusion reactor. One of the chief problems in the manufacture of high-powered copper/polymer composite magnets is the difficulty to precisely control the fiber volume fraction. In this thesis, the effect of variations in fiber volume fraction on thermal stresses in copper/cyanate ester composite cylinders is investigated. The cylinder is a composite that uses copper wires that run longitudinally in a cyanate ester resin specifically developed by Composite Technology Development, Inc. This composite cylinder design is commonly used in magnets for nuclear fusion reactors. The application of this research is for magnets that use cylindrical coil geometry such as the Mega Amp Spherical Tokamak (MAST) in the UK. However, most stellarator magnet designs use complex geometries including the National Compact Stellarator Experiment (NCSX), and the Quasi-Poloidal Stellarator (QPS). Even though the actual stresses calculated for the cylindrical geometry may not be directly applicable to these projects, the relationship between fiber volume fraction and stresses will be useful for any geometry. The effect of fiber volume fraction on stresses produced by mechanical, thermal and magnetic loads on cylindrical magnet coils is studied using micromechanics with laminate plate theory (LPT) and finite element analysis (FEA). Based on the findings of this research, variations in volume fraction do significantly affect the stress experienced by the composite cylinder. Over a range of volume fractions from 0.3 to 0.5, the LPT results demonstrate that thermally induced stresses vary approximately 30% while stresses due to pressure vary negligibly. The FEA shows that magnetic stresses vary much less at around only 5%. FEA results seem to confirm the LPT model. It was also concluded that the stress in the insulation layers due to all types of loadings is significant and must be considered when using this system in fusion applications.

We present the phase behavior of soft sphere colloidal dispersions. The pH responsive and thermoresponsive microgels, poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc), were used as a new building block of colloidal crystals. The phase behavior of microgel dispersions was studied by different methods such as optical microscopy, particle trajectories, mean squared displacement (MSD) vs. lag time plots and radial distribution function. The results show that the phase of the sample relies on the particle concentration for dispersions of the same pH. As the pH approaches the pKa of microgels, the microgel dispersions show unusual crystalline phase at lower effective volume fraction than hard sphere melting transition. Also, at this pH regime, the microgel dispersions undergo slow and spatially heterogeneous crystal growth. The cooperative multi-body type attractive forces were proposed to explain the unusual stability at low effective volume fraction. Ion-dipole interactions were proposed to be the origin of the attractive forces. The melting point of bulk crystals at this pH regime is much higher than the volume phase transition temperature of the building block. These results are supportive of the attractive forces hypothesis.