Contribuições ao estudo da fluidodinâmica em leito de jorro: estudos experimentais e de simulação via CFD

Abstract

The spouted bed is characterized by establishing an effective contact between the phases and promoting a cyclical and uniform movement of the particles. This feature is of great industrial importance since most processes require an adequate rate of mass and energy transfer. However, depending on operating and geometric conditions the spouted bed can operate in an unstable regime thus reducing its efficiency. So, a better understanding about its fluid-dynamic behavior is necessary. In order to obtain velocity and porosity profiles in a conical-cylindrical spouted bed, an intrusive fiber optical technique was used. To validate the velocities measured by the probe a non-intrusive method composed by a high-speed video camera was used. As for the calibration of the probe to measure the porosity, it was considered the assumption of linearity between the intensity of the voltage signal captured by the probe and the concentration of solids in a given volume of measurement. The measurements were carried out at different air velocity conditions, diameters of glass spheres and heights in the spouted bed. An investigation about the disturbance caused to the flow by an intrusive technique was performed by recording the height variation and displacement of the fountain. In this work, the Computational Fluid Dynamics (CFD), using the Eulerian Granular Multiphase model was used to determine the porosity and velocity profiles and numerical analysis of the flow disturbance caused by the introduction of the probe under the same experimental conditions. The following drag models were investigated: GIDASPOW et al. (1992), GIDASPOW (1994) and RUC (1994). The GIDASPOW model found in the Fluent® user guide was also used and, as it is written so erroneous in this user guide, small variations when compared to the correct model were obtained. The profiles obtained by simulations using the models GIDASPOW et al. (1992) and GIDASPOW (1994) appeared to underestimate the velocity values in the region of jet while the RUC model slightly overestimates the velocity values in the same region. In the annular region the simulations agree well with the experimental results regardless of the drag model used. It was possible for all conditions examined experimentally to foresee, by means of analysis of the profiles of solids volume fraction simulated, the disturbance caused by the introduction of the probe to the flow. Disturbance was detected with greater intensity in the region of jet and in the transition region between it and the annular region. The disturbance analysis is of great importance while simulating the properties of the flow obtained experimentally by means of an intrusive technique, because in practice the works on simulations present in the literature do not take the disturbance phenomenon into account.