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Estudo da influência de ondas acústicas em leitos fluidizados

Rodrigues, Alexandre Caires
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Dissertação
Português
Relevância na Pesquisa
17.940471%
Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2014.; Este trabalho avalia a influência de ondas acústicas sobre o carreamento de partículas em leitos fluidizados. Esse tipo de leito é utilizado em diferentes setores industriais tais como a indústria petroquímica, farmacêutica, alimentícia, gaseificação, etc. A ação de ondas acústicas no leito fluidizado pode alterar parâmetros tais como as taxas de transferência de calor, de transporte de massa e de mistura do leito. A influência sobre o carreamento de partículas será estudado mais a fundo. Foi construida uma bancada laboratorial composta por um reator de fluidização, sistema de aquisição de dados e um sistema de captura de partículas expelidas, onde foram experimentados leitos de vermiculita com e sem a atuação de ondas acústicas, com a finalidade de constatar a influência dessas ondas no carreamento das partículas. Foi conduzido também um estudo numérico dos principais parâmetros acústicos e de fluidização sobre o comportamento das partículas. Tanto os experimentos quanto os estudos numéricos indicaram a influência dos campos acústicos no carreamento de partículas em leitos fluidizados. ______________________________________________________________________________ ABSTRACT; This study evaluates the influence of acoustic waves on the carrying of particles in fluidized beds. This sort of bed is used in different industries...

Monitoring Fluidized Bed Drying of Pharmaceutical Granules

Briens, Lauren; Bojarra, Megan
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Publicado em 09/11/2010 Português
Relevância na Pesquisa
17.833022%
Placebo granules consisting of lactose monohydrate, corn starch, and polyvinylpyrrolidone were prepared using de-ionized water in a high-shear mixer and dried in a conical fluidized bed dryer at various superficial gas velocities. Acoustic, vibration, and pressure data obtained over the course of drying was analyzed using various statistical, frequency, fractal, and chaos techniques. Traditional monitoring methods were also used for reference. Analysis of the vibration data showed that the acceleration levels decreased during drying and reached a plateau once the granules had reached a final moisture content of 1–2 wt.%; this plateau did not differ significantly between superficial gas velocities, indicating a potential criterion to support drying endpoint identification. Acoustic emissions could not reliably identify the drying endpoint. However, high kurtosis values of acoustic emissions measured in the filtered air exhaust corresponded to high entrainment rates. This could be used for process control to adjust the fluidization gas velocity to allow drying to continue rapidly while minimizing entrainment and possible product losses.

Modeling Impact Cratering in Layered Surfaces

Senft, Laurel E.; Stewart, Sarah
Fonte: American Geophysical Union Publicador: American Geophysical Union
Português
Relevância na Pesquisa
27.325083%
Impact craters are potentially powerful tools for probing large-scale structure beneath planetary surfaces. However, the details of how target structure affects the impact cratering process and final crater forms remain poorly understood. Here, we present a study of cratering in layered surfaces using numerical simulations. We implement the rheologic model for geologic materials described by Collins et al. ( 2004) into the shock physics code CTH; this model includes pressure, temperature, and damage effects on strength as well the option to include acoustic fluidization. The model produces reasonable final crater shapes and damaged zones from laboratory to planetary scales. We show the effects of varying material strength parameters and discuss choosing appropriate strength parameters for laboratory and planetary situations. Results for cratering into idealized terrains with layers of differing material strength are presented. The presence of such layers in the target can significantly alter the ejecta curtain structure and the final crater morphology. Finally, we reproduce the morphologic variations that are observed in small lunar craters by modeling a weak regolith overlying competent rock.; Earth and Planetary Sciences

Magnetic fabric of Araguainha complex impact structure (Central Brazil): implications for deformation mechanisms and central uplift formation

Yokoyama, Elder; Trindade, Ricardo Ivan Ferreira da; Lana, Cristiano de Carvalho; Souza Filho, Carlos Roberto de; Baratoux, D.; Marangoni, Y?ra Regina; Tohver, Eric
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Relevância na Pesquisa
28.196987%
The weakening mechanisms involved in the collapse of compleximpact craters are controversial. The Araguainhaimpact crater, in Brazil, exposes a complexstructure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (< 10 ?m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magneticfabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of compleximpactstructures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
48.6537%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: Elsevier; Amsterdam Publicador: Elsevier; Amsterdam
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.196987%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Acoustic fluidization for earthquakes?

Sornette, D.; Sornette, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/01/2000 Português
Relevância na Pesquisa
48.6537%
Melosh [1996] has suggested that acoustic fluidization could provide an alternative to theories that are invoked as explanations for why some crustal faults appear to be weak. We show that there is a subtle but profound inconsistency in the theory that unfortunately invalidates the results. We propose possible remedies but must acknowledge that the relevance of acoustic fluidization remains an open question.; Comment: 13 pages

Mechanochemistry: an hypothesis for shallow earthquakes

Sornette, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/07/1998 Português
Relevância na Pesquisa
17.325082%
We advance the novel hypothesis that water in the presence of finite localized strain within fault gouges may lead to the phase transformation of stable minerals into metastable polymorphs of higher free energy density. Under increasing strain, the transformed minerals eventually become unstable, as shown from an application of Landau theory of structural phase transitions. We propose that this instability leads to an explosive transformation, creating a slightly supersonic shock wave propagating along the altered fault core leaving a wake of shaking fragments. As long as the resulting high-frequency acoustic waves remain of sufficient amplitude to lead to a fluidization of the fault core, the fault is unlocked and free to slip under the effect of the tectonic stress, thus releasing the elastic part of the stored energy. We briefly discuss observations that could be understood within this theory.; Comment: 36 pages, 2 ps figures, to appear in "Earthquake Thermodynamics and Phase Transformations in the Earth's Interior" - Roman Teisseyre and Eugeniusz Majewski (eds), Cambridge University Press

Local fluidization of a granular packing under focused ultrasound

Lidon, Pierre; Taberlet, Nicolas; Manneville, Sebastien
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.371592%
We report experimental results on the dynamics of a granular packing submitted to high-intensity focused ultrasound. Acoustic radiation pressure is shown to remotely induce local rearrangements within a pile as well as global motion around the focal spot in an initially jammed system. We further demonstrate that this fluidization process is intermittent for a range of acoustic pressures and hysteretic when the pressure is cycled. Experimental results are reproduced in numerical simulations in which the acoustic pressure field is modeled by a localized external force. Finally a simple two-state model is presented and recovers the intermittent, first-order-like unjamming transition observed experimentally and numerically.; Comment: 5 pages, 4 figures + supplemental material