EM - Escola de Minas

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Twenty million years of post-orogenic fluid production and hydrothermal mineralization across the external Araçuaí orogen and adjacent São Francisco craton, SE Brazil.
(2019) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Buick, Ian S.; Alkmim, Fernando Flecha de; Cipriano, Ricardo Augusto Scholz; Queiroga, Gláucia Nascimento
The Araçuaí orogen (AO) is a hot orogenic system that is known for its widespread and long-lived magmatism (630–480 Ma).Within the last c. 20 million years of its evolution, the AO saw the widespread development of hydrothermal systems in its lower-grade external fold-and-thrust belt and its Foreland Domain (eastern margin of the adjoining São Francisco craton). U\\Pb crystallization ages for hydrothermal monazite, rutile, and xenotime indicate that fluid circulation along the entire AO occurred between 515 to ca. 495 Ma, largely overlapping with U\\Pb ages of hydrothermal systems and mineralized zones in the adjacent São Francisco craton. Titanium-inquartz thermometry suggests that most hydrothermal systems closed at temperatures of ca. 360 °C. The Sm\\Nd isotope composition of the vein monazite samples ranges from εNd500Ma −16.8 to −17.8, and one less-evolved sample with εNd500Ma of −5.9. The Sm\\Nd isotope compositions overlap with the bulk rock Sm\\Nd data for the Espinhaço Supergroup, suggesting that the hydrothermal veins in this study are mainly related to metamorphic fluids derived from the prograde dehydration of low-grade metasedimentary rocks. The U\\Pb ages, Sm\\Nd isotope composition, and vein mineralogy are all consistent with a 20 My period of channelized fluid flow, characterized by an oxidizing, low pH, REE-, P-, and Ti-bearing aqueous metamorphic fluid. The expression of supercritical fluid flow in the core of the AO is given by the emplacement of large volumes of bare/mineralized pegmatite bodies and regional resetting of monazite ages in host rocks. On a regional context, this widespread fluid flow is associated with a high-T, low-P metamorphism that marks the beginning of the post-collisional decompression of the orogeny, which is associated with lithospheric mantle delamination. The reorganization of mass and heat, due to extensional collapse, resulted in multi-sourced fluid production and mineralization from deep to shallow crustal levels that affected an area of over 400.000 km2 along the eastern border of the São Francisco Craton.
Influência da configuração da SEN no comportamento fluidodinâmico em molde de Beam Blank.
(2017) Gabriel, Weslei Viana; Peixoto, Johne Jesus Mol; Alves, Gesiane Letícia; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Seshadri, Varadarajan
Utilizando técnicas de modelagem física e matemática comparou-se o fluxo de fluido no interior do molde de beam blank alimentado por apenas uma válvula submersa, com 3 e 4 portas na saída respectivamente. Na válvula com 4 portas, observou-se que para um diâmetro da porta de saída inferior de 10mm não houve alterações significativas no comportamento do fluxo, comparado à válvula com apenas três portas laterais. Ao aumentar o diâmetro para 16mm, houve alteração significativa do perfil de velocidade, reduzindo a assimetria de fluxo, fato que pode contribuir para a redução no gradiente térmico ao longo do molde, diminuindo a possibilidade de ocorrência de defeitos no material lingotado. Com o aumento da dimensão da porta inferior observou-se também redução na velocidade de impacto do jato principal e consequentemente reduziu-se a velocidade do fluxo ascendente, o que evita refusão da pele e entranhamento de escória.
Fluid flow and mixing characteristics in RH degasser of Companhia Siderúrgica de Tubarão, and influence of bottom gas injection and nozzle blockage through physical modelling study.
(2004) Silva, Carlos Antônio da; Silva, Itavahn Alves da; Martins, Ernani Márcio de Castro; Seshadri, Varadarajan; Perim, Carlos Alberto; Vargas Filho, Geraldo Alves
A physical model based on similarity principles has been constructed for simulating the RH degasser of Companhia Sideru´rgica de Tubara˜o (CST), Vito´ ria, ES, Brazil. The influence of gas injection through nozzles in the upleg with simultaneous bottom injection of gas, as well as the influence of nozzle blockage, on the circulation rate has been investigated. In addition, mathematical relationships for mixing characteristics in the process have been evaluated.
Computational and physical simulation of fluid flow inside a beamblank continuous casting mold.
(2016) Peixoto, Johne Jesus Mol; Gabriel, Weslei Viana; Ribeiro, Leticia Queiroz; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Seshadri, Varadarajan
The main features of the flow field inside a beam blank continuous casting mold have been assessedthrough mathematical and physical modeling techniques. Experimental techniques such as particle dis-persion through addition of dye and particle image velocimetry have been used in a physical model of themold to assess the flow pattern. Different combinations of nozzle geometry and throughput have beenemployed and the experimental results have been analyzed. In the case of two tubular nozzles, whichshould ensure good thermal and flow symmetry, six vortices were observed in the mold, two near theweb and two in each of the flanges. Increasing the flow rate of the fluid from 100 L/min to 150 L/minleads to a change from 0.74 m to 0.84 m in the jet penetration depth. However even a 67% increase ofthe nozzle cross section did not affect this parameter significantly. Experiments with one single tubularnozzle (53.2 mm inside diameter) were also carried out and the resulting flow asymmetry has been char-acterized. The difference in the fluid velocities at the filets could lead to unequal solid shell growth. Thedepth of jet penetration is larger than mold nominal length (0.8 m). Fluid flow structure as determinedby PIV measurements and CFD simulations show a good agreement.

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