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The Role of Manganese in the Formation of Proeutectoid FerriteGilmour, James Buell 09 1900 (has links)
<p> The Fe-C-Mn phase diagram has been calculated from thermodynamic data. Experimentally determined tie-lines are in good agreement with the calculated diagram. </p> <p> It has been shown that the assumption that the austenite-ferrite interface is in a local equilibrium condition during the late stages of the transformation in highly supersaturated alloys and at all times in alloys in an area of low supersaturation is justified. The approximate solution to the diffusion equations correctly predicts the experimentally determined manganese concentration profiles. </p> <p> Hillert's concept of paraequilibrium has been examined and explicitly defined. The concentration given by a paraequilibrium calculation correctly predicts the experimentally observed growth rates of Kinsman and Aaronson (1967) for very highly supersaturated alloys. </p> <p> A convolution technique for use in the interpretation of strongly localized concentration changes determined by electron beam microanalysis has been developed. </p> / Thesis / Doctor of Philosophy (PhD)
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Advances in calculation of minimum miscibility pressureAhmadi Rahmataba, Kaveh 09 June 2011 (has links)
Minimum miscibility pressure (MMP) is a key parameter in the design of gas flooding. There are experimental and computational methods to determine MMP. Computational methods are fast and convenient alternatives to otherwise slow and expensive experimental procedures. This research focuses on the computational aspects of MMP estimation. It investigates the shortcomings of the current computational models and offers ways to improve the robustness of MMP estimation. First, we develop a new mixing cell method of estimating MMP that, unlike previous "mixing cell" methods, uses a variable number of cells and is independent of gas-oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method relies entirely on robust P-T flash calculations using any cubic equation-of-state (EOS). We show that mixing cell MMPs are comparable with those of other analytical and experimental methods, and that our mixing cell method finds all the key tie lines predicted by MOC; however, the method proved to be more robust and reliable than current analytical methods. Second, we identify a number of problems with analytical methods of MMP estimation, and demonstrate them using real oil characterization examples. We show that the current MOC results, which assume that shocks exist from one key tie line to the next may not be reliable and may lead to large errors in MMP estimation. In such cases, the key tie lines determined using the MOC method do not control miscibility, likely as a result of the onset of L₁-L₂-V behavior. We explain the problem with a simplified pseudo-ternary model and offer a procedure for determining when an error exists and for improving the results. Finally, we present a simple mathematical model for predicting the MMP of contaminated gas. Injection-gas compositions often vary during the life of a gasflood because of reinjection and mixing of fluids in situ. Determining the MMP by slim-tube or other methods for each possible variation in the gas-mixture composition is impractical. Our method gives an easy and accurate way to determine impure CO₂ MMPs for variable field solvent compositions on the basis of just a few MMPs. Alternatively, the approach could be used to estimate the enrichment level required to lower the MMP to a desired pressure. / text
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Modelos de otimização para avaliação de investimentos em redes de distribuição de energia elétrica considerando índices de confiabilidade / Optimization models for evaluation of investiment in electrical distribution network considering indexes reliabilityCaetano, Ana Paula Pereira Tsuyuguchi 20 March 2015 (has links)
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Previous issue date: 2015-03-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The simulation results obtained using three models which minimize the distribution
system reliability indexes and investment through sectionalizing switches allocation and/ or
installation of tie lines are presented in this work. This is a problem with conflicting goals that
were simultaneously minimized through a multi-objective Genetic Algorithm (Non-
Dominated Sorting Genetic Algorithm II - NSGA II), seeking trade-off solutions between
investment costs and network reliability. As constraints, the continuity indexes (DEC and
FEC) and the power flow of the system were considered.
The three models presented have two objective functions, being the first one the
investment cost (CINV) of allocated equipment. The second function is one of three reliability
indexes: Cost of Energy not Supplied (CENS), DEC and FEC.
In the first model (CINV and CENS), results with higher quantities of sectionalizing
switches allocation were found, so it was the model which presented higher investment costs.
In the second model (CINV and DEC) results presenting lower values for the DEC were
found, comparing with the first model, and lower investment cost, but the total cost were
similar to those of the first model, since it has an increased CENS. The third model (CINV
and FEC) was the model which allocated less sectionalizing switches and presented lower
investment costs, since the allocation of these devices do not influence the minimization of
FEC, only the allocation of tie lines change the system configuration influencing the FEC.
All results obtained through the models met the expectations of finding a set of diverse
solution considering the constraints. / Neste trabalho foram apresentados e analisados os resultados obtidos de três modelos
matemáticos que minimizam indicadores de confiabilidade do sistema de distribuição e custo
de investimento através da alocação de chaves seccionadoras e/ou instalação de ramais de
interconexão. Trata-se de um problema com objetivos conflitantes que foram minimizados
simultaneamente através de um algoritmo genético multiobjetivo (Non-Dominated Sorting
Genetic Algorithm II NSGA II), buscando soluções com bons compromissos (trade-off)
entre o custo de investimento e a confiabilidade da rede. Foram considerados como restrições
os indicadores de continuidade (DEC e FEC) e o fluxo de potência do sistema.
Os três modelos apresentados possuem duas funções objetivos, uma das funções
representa o custo de investimento (CINV) dos equipamentos alocados e a outra função é um
indicador de confiabilidade, sendo que foram adotados o custo de energia não suprida (CENS)
e os indicadores DEC e FEC respectivamente ao primeiro, segundo e terceiro modelo.
No primeiro modelo (CENS e CINV) foram encontrados resultados com maior
quantidade de alocação de chaves, deste modo foi o modelo que apresentou maiores custos de
investimentos. No segundo modelo (DEC e CINV) foram encontrados resultados com
menores valores para o DEC em relação ao primeiro modelo e com menor custo de
investimento, porém com custo total aproximados dos valores do primeiro modelo, visto que
tiveram um aumento do CENS. O terceiro modelo (FEC e CINV) foi o modelo que menos
alocou chaves seccionadoras e apresentou menores custos de investimento, uma vez que a
alocação destes dispositivos não influencia na minimização do FEC, somente a alocação dos
ramais de interconexão que alteram a configuração do sistema influenciando no FEC.
Todos os resultados obtidos nos modelos atenderam às expectativas de encontrar um
conjunto de solução diversificado respeitando as restrições impostas.
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