RCAAP Repository

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

In situ instrumented indentation tests (IIT) can be used to determine tensile properties as a non-destructive alternative to the destructive tension test, especially when the removal of large amounts of test material from in-service structures implies high cost due to the interruption of operations. The ability of the analytical methods proposed by Haggag et al. and by Ahn and Kwon for determination of yield strength and ultimate tensile strength was assessed by instrumented indentation tests performed on steels for the oil and gas industry. For the analytical method proposed by Haggag et al. , the use of the material parameters Bm= 0.2285 and Xm= 1.200, employed for steels in several studies, proved unable to determine the tensile properties of steels analyzed in the present work. It was found that the indentation results were not in agreement with the tensile data (error up to 35%). Statistical analysis indicated that the empirical parameters Bm and Xm depend on both the indenter diameter and the maximum indentation load. An alternative for determining the tensile properties of steels using Haggag s Model is presented, based on the incorporation of the yield offset parameter, bm, and new values for the parameters Bm, bm and Xm. Use of different empirical correlations for estimating the yield strength and tensile strength from indentation hardness measurements was also investigated. The methodology here proposed validated the instrumented indentation test for determination of tensile properties of steels within a range of error of 10%. Furthermore, tests performed on ABNT 8550 steel specimens, exposed to a high hydrogen pressure, suggest that the instrumented indentation test may be applicable for hydrogen embrittlement detection in steels.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Electrical submersible pumping (ESP) is one of the artificial oil lifting methods employed in wells that do not have enough energy to raise the oil naturally to the surface. These pumps work in harsh conditions when pumping water mixed with gases and sand particles. Sand production causes losses in this operation, such as loss of efficiency and critical damage to internal parts. In this study, the effects of the abrasive particle size of sand on the wear of electrical submersible pumps were evaluated. Two pumps were tested, one using sand with an average diameter of 225 m and another using extra-fine sand with an average diameter of 70 m. During the tests, the pump performance curve and its vibration were monitored. Additionally, the bearing clearances and masses of the rotors and diffusers were measured before the beginning and after the end of the tests. The results showed that the worst operating conditions occur when sand of smaller grain sizes was used, since it enhances the bearing wear that leads to a faster radial instability. It was also observed that using abrasive particles of greater sizes leads to high erosive wear, especially in diffusers. In the diffuser region with the thinner cross section the most pronounced erosive wear was noticed.

O desgaste erosivo é geralmente um fator decisivo na ruptura de gasodutos. Muitos processos industriais que necessitam transportar partículas erosivas estão diretamente expostos a problemas de vazamento ou de contaminação. Como resultado, custos desnecessários são usados em operações de manutenção. Essa preocupação industrial é responsável por motivar os pesquisadores a desenvolver ferramentas de análise que possam quantificar com precisão o problema da erosão. Devido a esse fato, para validar o modelo de CFD, os resultados numéricos para o cotovelo padrão são comparados com dados experimentais. Depois disso, uma câmara de vórtice foi adicionada ao cotovelo padrão, mantendo as mesmas características geométricas (e.g., diâmetro e raio de curvatura), bem como os parâmetros de simulação (e.g., velocidade inicial, densidade, viscosidade, etc.). Com base em simulações com quatro vias de acoplamento do escoamento gás-sólido em ambas geometrias, a comparação entre os resultados de cotovelo padrão e do cotovelo com câmara de vórtice foi realizada e uma análise detalhada da influência da carga mássica no escoamento e na taxa de penetração foi obtida. O presente trabalho utilizou o código de volumes finitos UNSCYFL3D, que resolve o escoamento de gás usando a abordagem de Euler-Lagrange totalmente acoplada. O modelo k-epsilon duas camadas foi usado para modelar os efeitos de turbulência. Curiosamente, os resultados mostram que a taxa de penetração no cotovelo com câmara de vórtice não reduz exponencialmente com o aumento da carga mássica, contradizendo o comportamento observado no cotovelo padrão. Outra descoberta importante é que a adição da câmara de vórtice mostra significativamente a eficiência do efeito de amortecimento. Comparando-se o pico da taxa de penetração em ambos os modelos de cotovelo para uma carga mássica de 1.0, a redução foi cerca de 93 % quando a câmara de vórtice está presente. Com base em análises numéricas do escoamento de gás-sólido acoplado, o mecanismo físico do efeito de amortecimento é proposto.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

This works focus on practical solutions for cooling systems that contribute to solve the problem of environmental degradation. The aim is to change the original cooling system working fluid, and identify in the universe of choices, the best alternative fluid. Thus, a experimental facility was built and, is consisted of a scroll compressor with capacity of 12 kW, originally designed for R22, as well as tube-in-tube heat exchangers and an electronic expansion valve (VEE). The system was properly instrumented, in order to enable the assessment of cooling capacity and COP. Each replacement on the original system, so, each drop-in process, contributes to confirming the uniqueness of the scroll compressor applications. In the beginning, tests were carried out to build the response surface and metamodels, so enable analyze the system boundaries. After this, new tests were carried out in all operation range. Starting with the operation frequency of 60 Hz and 100% opening VEE. Later, the boundaries of each the alternative refrigerant were tested. The results showed restriction to the type of fluid tested as well as to the operating conditions of the vapor compression cycle. The hydrocarbon (HC) R1270 operated in a limited conditions whereas R410A even reached steady state conditions. Refrigerants that showed better adaptation to the cooling system were HFCs R404A, R438A and R134a. In sequence, it was conducted performance analysis for each refrigerant operating with 90% of initial charge. As a result it was achieved a slight expansion of the system application region, however, the COP values were the lowest ones, except for the R404A. Finally, the estimation of environmental impacts of each fluid was calculated by the TEWI method. The R1270, even with operating limitations, showed the best results, while the R438A presented the worst result for the environment.