This work investigates the effects of long range hydrodynamic fibre-fibre interactions on the orientation state of a semi-dilute, rigid fibre suspension flowing through a linear contracting channel under laminar flow conditions. The effects of fibre-fibre interactions are modeled mathematically, the governing equations solved numerically and the predicted results compared with experimental observations. The theoretical model is based on the assumption that the orientation state of the suspension can be completely described by a probability distribution function and that fibre-fibre interactions are random in nature, thus giving rise to a diffusion-type process. The orientation distribution evolves spatially according to a Fokker-Plank type equation using closure equations for the rotary diffusion coefficient advanced by either (i) Folgar and Tucker (J. Reinforced Plast. Comp. 3 98–119 1984) or (ii) Koch (Phys. Fluids 7(8) 2086–2088 1995). Each of these two closure models for the rotary diffusion coefficient contains an unknown empirical constant that must be determined from experiments. These were fit to experimental data along the central streamline of the contraction as a function of fibre concentration. The diffusion coefficient was found to first increase with increasing suspension concentration up to a maximum, and then decrease with concentration above this point. This non-monotonic behavior was attributed to fibre flocculation, a mechanism not considered in the relationships for the rotary diffusion coefficient. The theoretical model is then extended to predict fibre orientation over the entire plane of the contraction and the two-way momentum coupling between the fluid and fibre phases were investigated numerically. The results show that the structure of the flow field within the contraction is significantly altered when the fibre phase is considered, demonstrating the non-negligible effect of the momentum exchange between the two phases. Comparison is made between the predicted orientation state of the suspension with experimental observations over the contraction plane. Good agreement was found between the model predictions and the experimental observations except in a small region near the solid boundaries. These near wall discrepancies were attributed to an inability to correctly handle the wall boundary conditions in the fibre orientation model. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Orientador: Milton Mori / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-18T19:12:31Z (GMT). No. of bitstreams: 1 PrietoJimenez_Natalia_M.pdf: 6938239 bytes, checksum: 6c44d3053179a676042ac55971eeb06b (MD5) Previous issue date: 2011 / Resumo: Craqueamento Catalítico Fluidizado (FCC) é um processo amplamente utilizado para converter frações de hidrocarbonetos de óleos brutos de petróleo com elevado ponto de ebulição, a produtos mais valiosos tais como gasolina e gases olefínicos (alcenos). Durante as reações de craqueamento, o catalisador é desativado rapidamente devido à deposição de coque na sua superfície. Em unidades industriais de FCC, o catalisador desativado é continuamente regenerado utilizando um regenerador, conectado ao reator riser. Além da regeneração do catalisador (combustão de coque pelo contato com o ar), o regenerador FCC fornece também a energia necessária para as reações de craqueamento endotérmicas. O objetivo deste trabalho de pesquisa é simular a combustão de coque em um regenerador tridimensional, analisado variáveis de saída como concentração de carbono, temperatura, velocidade axial e radial das fases sólida e gasosa, e fração volumétrica de sólidos, mediante a técnica de Fluidodinâmica Computacional (CFD). Para isto, são utilizadas duas configurações de regenerador com dimensões e condições de contorno tomadas da literatura. Para a modelagem matemática e numérica utilizaram-se os softwares comerciais ANSYS-CFX V11 e FLUENT V12, junto com sub-rotinas desenvolvidas durante a pesquisa. Foram comparados sistemas de reação homogênea e heterogênea utilizando o modelo cinético Finite-Rate laminar, no qual as taxas de reação são determinadas pelas expressões cinéticas de Arrhenius. Do desenvolvimento das simulações obtiveram-se resultados satisfatórios que serão úteis no entendimento do complexo processo da regeneração de catalisadores para processos de FCC / Abstract: Fluidized Catalytic Cracking (FCC) is a widely used process to convert hydrocarbon fractions of crude petroleum oils with high boiling point to more valuable products such as gasoline and olefin gases (alkenes). During the cracking reactions, the catalyst is quickly deactivated due to coke deposition on its surface. In FCC industrial units, deactivated catalyst is continuously regenerated using a regenerator, connected to the riser reactor. In addition to catalyst regeneration (coke combustion by contact with air), FCC regenerator also provides the necessary energy for endothermic cracking reactions. The aim of this research was to simulate the coke combustion in a three-dimensional regenerator, analyzing output variables as coke concentration, temperature, axial and radial velocity of solid and gaseous phases, and solid volume fraction through the technique of Computational Fluid Dynamics (CFD). For this purpose two configurations of regenerator were used with dimensions and boundary conditions taken from the literature. For mathematical and numerical modeling, the commercial software ANSYS-CFX V11 and FLUENT V12 were used, with subroutines developed during the research. Homogeneous and heterogeneous reaction systems were compared using the laminar Finite-Rate kinetic model, in which the reaction rates are determined by Arrhenius kinetic expressions. The simulation of this system produced satisfactory results that will be useful in understanding the complex process of catalyst regeneration for FCC processes / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

No description available.

No description available.

Thesis: M.S., Massachusetts Institute of Technology, Department of Chemical Engineering, 1982 / Bibliography: leaves 59-60. / by Willie K. Chan. / M.S. / M.S. Massachusetts Institute of Technology, Department of Chemical Engineering

No description available.

No description available.

No description available.

No description available.

No description available.