Made available in DSpace on 2014-06-11T19:34:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-09-10Bitstream added on 2014-06-13T19:24:02Z : No. of bitstreams: 1 anazawa_rm_dr_guara.pdf: 10651017 bytes, checksum: 16ae1ffa0b957dba762c69ee5a3bb352 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os aços multifásicos são de grande interesse comercial e têm atraído a atenção, principalmente, da indústria automobilística devido a combinação de alta resistência e ductilidade. A fase austenita retida, presente nestes aços, tem sido objeto de especial interesse devido ao efeito TRIP, que contribui para a melhoria da tenacidade. Neste trabalho é utilizado o aço aeronáutico 300M e, com o objetivo de estudar a influência das fases sobre as propriedades mecânicas são realizadas as seguintes etapas: a otimização de rotas de tratamentos térmicos para a obtenção de uma microestrutura multifásica; caracterização microestrutural por microscopia óptica, microscopia eletrônica de varredura e microscopia de força atômica e avaliação do envelhecimento de deformação à temperatura ambiente. A principal contribuição é a determinação da fração volumétrica da austenita retida por meio de medidas de saturação magnética através de curvas de histerese magnética. As frações volumétricas de austenita retida obtidas por medidas de magnetização são comparadas com as obtidas por difratometria de raios X e microscopia óptica após ataques químicos de metabissulfito de sódio. Os resultados obtidos por microscopia óptica e pelo método magnético apresentam boa concordância com os valores encontrados na literatura. A alteração microestrutural devido aos tratamentos térmicos aplicados permite melhorias no limite de escoamento e resistência. Analisa-se, ainda, o efeito do envelhecimento por deformação à temperatura ambiente. Os resultados são surpreendentes, ocorrendo um aumento no limite de escoamento em até 87%, devido à associação do envelhecimento por deformação com o efeito TRIP. / The multiphase steels are of great commercial interest and have attracted attention mainly of the automobile industry due to the combination of their high strength and ductility. The retained austenite phase present in these steels has been object of special interest due to TRIP effect contribution for the improvement of the toughness. In this work the influence of the phases of the aircraft 300M steel is carried out by the optimization of heat treatments routes to obtain multiphase microstructure. Microestructural characterization is evaluated by optical microscopy, scanning electronic microscopy, atomic force microscopy and analysis of the deformation ageing at room temperature. The main contribution is the determination of retained austenite volume fractions from magnetic hysteresis curves. These values are compared with x-ray diffraction data and optical microscopy after sodium metabisulfite etching, presenting good agreement with the literature. The microstructural alterations due the applied heat treatments also affect the yield strength and strength. The association of the deformation ageing and the TRIP effect resulted in a surprising increase of up to 87% in the yield strength.

Orientador: Tomaz Manabu Hashimoto / Banca: Marcelo dos Santos Pereira / Banca: Alfeu Saraiva Ramos / Banca: Jorge Otubo / Banca: Rosinei Batista Ribeiro / Resumo: Os aços multifásicos constituídos de ferrita, bainita, austenita retida e martensita apresentam combinações muito atrativas de resistência e tenacidade. Há ainda um potencial adicional de melhorias de propriedades mecânicas quando a fração de austenita retida for alta, conferindo alta conformabilidade pelo efeito TRIP. Neste contexto, é fundamental a análise qualitativa e quantitativa das fases, especialmente de austenita retida e sua transformação em martensita induzida por deformação. Este trabalho enfoca a transformação da austenita retida em martensita por deformação em tração monotônica em um aço AISI 4340 com estrutura multifásica. Os resultados confirmam a transformação da austenita retida em martensita atingindo cerca de 80% de transformação. As frações volumétricas de austenita retida antes e após a deformação foram estimadas por duas técnicas. A primeira foi feita por análise de imagens em microscopia óptica e a segunda por magnetização de saturação, tendo em vista o caráter paramagnético desta fase. As frações estimadas pelas duas técnicas foram comparadas, concluindo-se que o método magnético deve ser reavaliado, tendo sido proposto um fator de correção na equação básica deste processo e presenta na literatura. / Abstract: The multiphase steels made of ferrite, bainite, retained austenite and martensite present very attractive combinations and toughness. There is still an additional potential of improvement of the mechanical properties when the fraction of retained austenite is high allowing high conformability by the TRIP effect. In this context the qualitative and quantitative analysis of the phases is essentual specially from retained austenite and its transformation in martensite induced by deformation. This work focus on the transformation of retained austenite in martensite by the deformation in monotonic traction in one steel AISI 4340 with multiphasic structure. The results confirm the transformation of retained in martensite reaching about 80% of transformation. The volumetric of retained austenite before and after the deformation were estimated by two technique: the first was made by the anllysis of images in optic microscopy and the second by magnetization of saturation taking into consideration the paramagnetica character of this phase. The estimated fraction by the two technique were compared leading to the conclusion that the magnetic method must be evaluated again using a proposed factor of correction in the basic equation of this process and present in the literature. / Doutor

Orientador: Milton Mori / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T21:12:35Z (GMT). No. of bitstreams: 1 SanchezForero_DianaIsabel_M.pdf: 2538568 bytes, checksum: 6a7cfe0d2a9575933ee82525a5cec615 (MD5) Previous issue date: 2012 / Resumo: Colunas de bolhas são dispositivos de contato multifásico para transferência de massa e calor, intensamente utilizados em diferentes áreas industriais. O escoamento e a turbulência destes equipamentos são induzidos pelo movimento ascendente das bolhas. A hidrodinâmica e o comportamento das bolhas em regime homogêneo foram analisados em uma coluna de bolhas retangular em escala de laboratório (50 cm x 20 cm x 220 cm), utilizando as técnicas de velocimetria por imagem de partícula (PIV) e a técnica de sombras Shadow para o estudo das fases contínua e dispersa, respectivamente. O gás foi alimentado através de um distribuidor de 18 furos a várias condições de velocidade superficiais de gás na entrada. As propriedades do escoamento para as duas fases foram determinadas por meio de uma quantidade suficiente de imagens duplas. O campo de velocidade para a fase contínua (líquido) foi obtido por adição de partículas traçadoras fluorescentes. Além disso, a intensidade de turbulência, energia cinética turbulenta e os tensores de Reynolds, foram determinados a partir dos dados obtidos pelas medições experimentais. Os resultados mostram o perfil típico da velocidade axial média do líquido, ascendente na região central e descendente nas proximidades das paredes da coluna. Também, foram encontradas diferenças entre os perfis normal e axial dos tensores, o que sugere que o fenômeno turbulento na coluna de bolhas é produzido pelo caráter anisotrópico desta. Finalmente, o comportamento das bolhas foi analisado determinando a distribuição e o tamanho destas. Verificou-se que o tamanho das bolhas decresce ao longo da coluna devido aos efeitos da deformação e fenômenos de coalescência. Igualmente, encontrou-se o diâmetro médio da bolha na faixa dos 4 milímetros, tamanho típico no regime homogêneo / Abstract: Bubble columns are multiphase contact devices for mass and heat transfer, wich are intensively used in different industrial areas. Flow and turbulence in these equipments are induced by the bubble rise motion. The hydrodynamics and bubble behavior in a homogeneous bubbly flow regime was analyzed in a rectangular laboratory-scale bubble column (50 x 20 x 220 cm) using Particle Image Velocimetry (PIV) and Shadow techniques to study continuous and dispersed phase, respectively. The bubble column was aerated by using 18 holes gas sparger for several superficial gas velocities. The flow properties for both phases were determinate by sufficient number of double images. The velocity field for continuous phase (liquid) was achieved by adding fluorescing tracer particles. In addition, turbulence intensities of the fluid, turbulent kinetic energy and tensors profiles were deduced from experimental measurements. Results show typical axial mean velocity profiles of the liquid, upward flow in the core region and a down-flow near the walls. Also, it was found differences between axial and normal tensors profiles that suggest the turbulent phenomena in the bubble column its produced by the anisotropic behavior. Finally the bubble performance was further analyzed by determining bubble distribution and bubble size. It was found a decreasing bubble size along the bubble column due to the coalescence and deformation effects. Furthermore, is determinate that the bubble diameter is around 4 mm, typical bubble size in a homogeneous bubble flow regime / Mestrado / Desenvolvimento de Processos Químicos / Mestra em Engenharia Química

This thesis investigates two methods of optical analysis of multiphase fluids. These two methods are nephelometry and the statistical analysis of scattered light intensity fluctuations. Nephelometry is an established technique for investigating particulate suspensions. In this work the basic technique is combined with neural network processing to develop a system capable of automatically distinguishing and quantifYing different suspensions, in particular suspensions of oil. Evidence obtained in this study suggests that neural networks can distinguish the light scattering from suspensions of different size distributions and produce a more accurate estimate of volume fraction than commonly used turbidity measurements. Non-Gaussian, fluctuating light intensities arise from the scattering of light from a varying population of suspended particles. Successful measurement of these intensity fluctuations makes feasible new instrumentation based on the statistical behaviour of the detected signal. Analyses that could prove possible include particle number, size, type and flow characteristics. Photon counting methods have traditionally been used to measure fluctuations from random media but the lower cost of analogue pin diodes makes them the preferred choice of detector if they can be applied usefully. A method of quantifYing the effect of noise from the diode detectors and removing it from the statistics of the fluctuations is developed from a model of the pin diode detectors. Experimental results show that detector noise can be compensated for in the analysis of scattered light fluctuations. Results also indicate that the model used to describe the scattering process is valid and that further work can lead to a practical instrument for the study of suspensions.

In November 2000, the 4th Workshop on Measurement Techniques for Stationary and Transient Multiphase Flows took place in Rossendorf. Three previous workshops of this series were national meetings; this time participants from different countries took part. The programme comprised 14 oral presentations, 9 of which are included in these proceedings in full length. A special highlight of the meeting was the main lecture "Ultrasonic doppler method for bubbly flow measurement" of Professor Masanori Aritomi, Dr. Hiroshige Kikura and Dr. Yumiko Suzuki, which was read by Dr. Hiroshige Kikura. The workshop again dealt with high-resolution phase distribution and phase velocity measurement techniques based on electrical conductivity, ultrasound, laser light and high-speed cinematography. A number of presentations were dedicated to the application of wire-mesh sensors developed by FZR for different applications used by the Technical Universities of Delft and Munich and the Tokyo Institute of Technology. The presentations were in particular: M. Aritomi, H. Kikura, Y. Suzuki (Tokyo Institute of Technology): Ultrasonic doppler method for bubbly flow measurement V. V. Kontelev, V. I. Melnikov (TU Nishny Novgorod): An ultrasonic mesh sensor for two-phase flow visualisation A. V. Duncev (TU Nishny Novgorod): Waveguide ultrasonic liquid level transducers for power generating equipment H.-M. Prasser, E. Krepper, D. Lucas, J. Zschau (FZR), D. Peters, G. Pietzsch, W. Taubert, M. Trepte (Teletronic Ingenieurbüro GmbH), Fast wire-mesh sensors for gas-liquid flows and decomposition of gas fraction profiles according to bubble size classes D. Scholz, C. Zippe (FZR): Validation of bubble size measurements with wire-mesh sensors by high-speed video observation A. Manera, H. Hartmann, W.J.M. de Kruijf, T.H.J.J. van der Hagen, R.F. Mudde, (TU Delft, IRI): Low-pressure dynamics of a natural-circulation two-phase flow loop H. Schmidt, O. Herbst, W. Kastner, W. Köhler (Siemens AG KWU): Measuring methods for the investigation of the flow phenomena during external pressure vessel cooling of the boiling water reactor SWR1000 A. Traichel, W. Kästner, S. Schefter, V. Schneider, S. Fleischer, T. Gocht, R. Hampel (HTWS Zittau/Görlitz - IPM): Verification of simulation results of mixture level transients and evaporation processes in level measurement systems using needle-shaped probes S. Richter, M. Aritomi (Tokyo Institute of Technology): Methods for studies on bubbly flow characteristics applying a new electrode-mesh tomograph

No description available.

In recent years, the lattice Boltzmann method (LBM) has emerged as a powerful tool that has replaced conventional macroscopic techniques like Computational Fluid Dynamics (CFD) in many applications. The LBM starts from meso- and microscopic Boltzmann's kinetic equation to determine macroscopic fluid dynamics. The origins of LBM can be drawn back to lattice gas cellular automata (LGCA); however it lacks Galilean invariance and creates statistical noise in the system. LBM on the other hand does away from these drawbacks of LGCA, and is easy to implement in complex geometries and can be used to study microscopic flow behavior in complex fluids/fluid mixtures. In this work, the LBM is used as a tool to study isothermal bubble dynamics of single and multiple bubbles in heavier fluids. Some benchmark problems have been solved to prove the effectiveness of LBM over conventional solvers and results have been compared to analytical/existing solutions. Flow behavior at different flow parameters have been recorded and presented. Bubble shape regimes have been classified based on the important two-phase flow parameters, namely the Eotvos number, Morton number, Reynolds number and the Weber number. Single bubble simulations have been conducted in fairly large domains to capture terminal velocities, which have been compared to existing theoretical solutions, obtained using the potential flow theory. The terminal velocities so obtained have also been used for the estimation of drag and drag coefficient for a range of Eotvos and Reynolds numbers, and the drag coefficient so computed has been compared with those predicted by existing correlations and analytical expressions. Bubble dynamics and collision and coalescence for multiple bubbles rising under the influence of gravity in fully periodic domains have been simulated using LBM, and the flow behavior around such bubbles prior to and after coalescence have been studied and the results presented. The study of multiple bubble dynamics reveals the influence of the wake on the shape and collision of downstream bubbles, and yields valuable insights into the physics of intermediate stages when multiple bubbles collide and form an elongated/stretched bubble. The flow and bubble coalescence behavior predicted in this study compares very well with experimentally captured bubble dynamics and with data present in literature. Possible extensions of the present study have been highlighted for future research.

The power requirements for microprocessors have been increasing per Moore's Law. According to International Technology Roadmap (ITRS), Voltage Regulator Module (VRM) for microprocessors will be about 200 W at 1 V output in 2010. With the VRM’s topology of synchronous buck, serious technical challenges such as small duty cycle, high switching frequencies, and higher current demands, contribute to decreased power density and increased cost. This thesis proposes a Continuous Input Current Multiphase Interleaved Buck topology to solve the technical challenges of powering future microprocessors. This new topology is aimed to improve past topologies by providing continuous input current and improved efficiency. An open loop system of the proposed new topology is simulated using OrCAD PSpice to evaluate the performance criteria of the VRM. A hardware prototype of a four-phase Continuous Input Current Multiphase Interleaved Buck Converter is constructed and tested to assess the targeted improvements.

The future of microprocessors is unknown. Over the past 40 years, their historical trend has been for adopting smaller and more powerful designs that drive the world that we live in today. The state of the microprocessor business today faces a crossroad, wishing to continue on the historical trend of doubling the number of transistors on a chip every 18 months (Moore’s Law) but also facing the realistic task of needing to power these sophisticated devices. With the low voltages and high currents that are required for these microprocessors to operate, it poses a difficult task for the future designers of the voltage regulators that are used to power these microprocessors. The technique that has been widely adopted as the preferred method to power these devices is called a multiphase buck converter, or multiphase voltage regulator. This thesis is a continuation of and is aimed to improve previous work done by two former Cal Poly students, Kay Ohn and Ian Waters. A new design that uses an interleaving control scheme, careful component selection, an input LC filter, and a reduction in board size seeks to improve the efficiency, input current noise, and increase the current density of the original design. Research was first conducted to determine how to best make such improvements. The design phase ensued, which used design calculations and simulations to test if the proposed multiphase topology was plausible. Once the theory was fully proven, a real hardware circuit was created and tested to confirm the results. The results yield a multiphase design with improved input noise filtering, greater efficiency, more equal current sharing, and higher current density as compared to previous topologies in this field. Parameters such as output voltage ripple, load and line regulation, and transient response remained excellent, as they were with the previous work.

No description available.