Modelagem fenomenologica e simulação bidimensional da fluidodinamica de reatores de leito fluidizado circulante




Circulating Fluidized Bed (CFB) reactors are used in a variety of industrial applications especially related to combustion and catalytic cracking. The fluid dynamic prediction of CFB is fundamental in its development and optimisation. In this work, a computer code for the simulation of the fluid dynamics of Circulating Fluidized Bed Reactors was developed. The Finite Volume Method was used to make the discretization of the mathematical model. The fluid dynamic model is based on the two fluid model, in which both the gas and particle phases are considered to be continuos and fully interpenetrating. With relation to mathematical model of CFB reactors, the sensitivity of the model to parameters of the Kinetic Theory of Granular Flows was analyzed. The effect of the turbulence transfer between the gas and particle phases was also analyzed. The k-Epsilon turbulence model, modified to consider the presence of the particle phase, was used to calculate the effective viscosity of the gas phase. Since there is no consensus about the effective stresses in the particle phases, the inviscid model, the Newtonian fluid model with experimentally obtained viscosity constant and the model of the emerging kinetic theory of granular flows (KTGF) have been used to simulate the fluid dynamics of the CFB reactors and the results were analysed. In the kinetic theory of granular flows the particle phase transport coefficients are dependent on the granular temperature, which intern has a transport equation. The granular temperature depends on parameters of the kinetic theory and also of the inlet conditions. The results confirm that the particles tends to concentrate in the regions of lower granular temperature, also showing a high sensitivity of the model to the parameters of the kinetic theory of granular flows, especially to the particle-particle and particle-wall coefficients of restitution. Further analyses showed that the interface turbulence transfer is very important for systems with high particle concentration and internal recirculations. With relation to the numerical method, in order to calculate the particle velocities at the faces of the control volumes, the results show that numerical oscillations are present when the calculation is carried out using linear interpolation of the particle phase velocities, in the collocated grid. The results also show that the numerical oscillation is eliminated by calculating the particle phase velocities at the faces of the control volumes by interpolating the particle phase momentum. The results were obtained by using a computer code developed by the authors. The finite volume method with the collocated grid, the hybrid interpolation scheme, the false time step strategy and the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm were used to obtain the numerical solution


modelos matematicos turbulencia metodos de simulação escoamento multifasico

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