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Made available in DSpace on 2014-10-09T12:53:25Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:32Z (GMT). No. of bitstreams: 1 12213.pdf: 5005382 bytes, checksum: c4bde457760b3a6d6f53b64c21e33010 (MD5) / No presente trabalho, foi utilizada a técnica de aquecimento por microondas para estudar a imobilização de rejeitos radioativos de nível de atividade baixo e médio, como resinas de troca iônica exauridas, empregadas na remoção de íons indesejáveis dos circuitos primários de refrigeração de reatores nucleares refrigerados a água, e aquelas usadas em colunas de separação química e radionuclídica no controle de qualidade de radioisótopos. Matrizes betuminosas reforçadas com alguns tipos de borrachas (Neoprene®, Silicone e Etileno Vinil Acetato - EVA), provenientes de material descartado ou sobras de produção, foram utilizadas para incorporação dos rejeitos radioativos. As irradiações das amostras foram feitas em um forno de microondas caseiro, que opera com freqüência de 2.450MHz e possui potência de 1.000W. As amostras foram caracterizadas, empregando-se ensaios de penetração, resistência à lixiviação, pontos de amolecimento, fulgor e combustão, termogravimetria e microscopia óptica. Os resultados obtidos mostraram-se compatíveis com os padrões dos componentes das matrizes, indicando que esta técnica é uma alternativa bastante útil aos métodos de imobilização convencionais e para esses tipos de rejeitos radioativos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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In gas turbines, the temperature behind the combustors is the highest, meaning that the blades in the first stage of the turbine require cooling air. This makes the structural blade model very detailed due to the presence of the cooling pattern. For aeromechanical design, one of the first steps is to perform a modal frequency check by using 3d Finite Element models and the Campbell diagram to establish if the design is acceptable with respect to resonance margins. If the 3d detailed geometry (including all the cooling details) is used the model becomes extremely large. In order to perform various loops between structural dynamics and aerodynamics in an early stage, the dynamic model of cooled blades should be simplified. The simplified model should be accurate enough in terms of predicting correct frequencies but much lighter in size.   The objective of this thesis is to perform parametric studies of different 3d simplified cooled turbine blade models. Various models with different geometrical features are created from the history of the CAD software (NX). Different FE meshes are produced in the Hypermesh software and the modal analyses are solved in Abaqus. The results are compared with the fully detailed model. The influence of the cooling features for each test case is summarized and this will be useful for creating reduced order models. Explanation and guidelines with respect to the mesh generation and loading conditions in Hypermesh software are also included in the appendix section.    For quick frequency checks during the intial stages of the design, the solid blade model can be used which has the modal frequencies within 10 percent range from the fully detailed model. The cooling core features that are important with respect to dynamics are cooling matrix, the ribs and the trailing edge cutback which contribute to the stiffness of the blade.

This research developed a double-side power electronics packaging scheme for high temperature applications exemplified by 1200 V, 150 A silicon devices. The power modules, based on both quarter and half-bridge topologies, were assembled using sintered silver device attachment rather than conventional solder alloys. Thermomechanical stresses in the double-side architecture were mitigated with a compliant layer fabricated from elliptical silver tubes. This research presents an introduction to conventional packaging techniques and their weaknesses. These shortcomings provide the basis for a module design which improves upon module thermal management while also addressing electrical and reliability requirements. The optimum package design enhances heat dissipation with the addition of a substrate bonded to the top electrical pads of the semiconductor devices. The use of sintered silver also increases the useful application temperature by avoiding the creep failure mechanisms of solder alloys. The modules were characterized extensively to quantify thermal and electrical performance. In the case of thermal characterization, the double-side architecture required multiple testing configurations to fully understand the parallel heat flow paths. These results were compared to models constructed using finite element analysis (FEA). The FEA models were also utilized for measurement of strains in multiple package designs to better determine the effects of increased compliance on the relative package cycling lifetime. These lifetimes were then assessed, in part, using experimental passive and cycling tests on functional double-side packages. The resulting power modules exhibited significant decreases in thermal resistance when they are cooled, as designed, from both sides of the module. Even single sided cooling options reveal significant advantages and transient thermal impedance was found to be significantly lower. Power module models revealed the compliant layer was successful in reducing the device shear stresses which was experimentally validated through the use of DC power stage testing. It was found, through double pulse testing and electrical modeling, that parasitic inductances were reduced by utilizing planar bonding and planar symmetrical traces. Finally, modeling of the double-side package with added tube compliance revealed a decrease in plastic and shear strains when compared to other single and double-side package designs. This reduction directly translates to increased cycling lifetime using well known strain based fatigue models. / Ph. D.