Fluidodinâmica e transferência de calor em leitos de jorro visando a secagem de grãos de Sorgo: análise experimental e simulação numérica por CFD-DEM e TFM

Abstract

Simulations of granular flows in spouted beds are carried out following two main approaches: two-fluid model (TFM) and CFD-DEM coupling (Computational Fluid Dynamics/Discrete Element Method). Moreover, the fluid dynamics of conical spouted beds with 3.20 mm grain sorghum were evaluated through experiments, TFM simulations (2D, and 3D), and CFD-DEM simulations. The gas-solid heat transfer was evaluated by experiments and through CFD-DEM simulations. To determine the input parameters of the CFD-DEM simulations, the direct measurement approach was used. Hence, devices were built to measure the restitution, static friction, and rolling friction coefficients to account for particle-particle and particle-wall interactions. First, the simulations were conducted from operational conditions, and experimental data to validate the model obtained from the literature. Subsequently, an experimental unit was constructed and fluid dynamic and heat transfer tests were performed. The simulations were conducted using the FLUENT® software. The geometries were built in DesignModeler and the computational grids generated in Meshing from the ANSYS® package, student version 19.1. With the experimental devices and employed methodologies, it was possible to obtain the material and interaction properties, which were essential to obtain satisfactory results in the CFD-DEM simulations. The behavior of the spouted bed was predicted with the CFD-DEM coupling, such as the transition stages from static bed to stable spouting conditions. In addition, the fluid dynamic characteristic curve was successfully simulated for both experimental units analyzed. For 2D and 3D TFM simulations, the pressure drop data as a function of air velocity (fluid dynamic characteristic curve) did not show the typical behavior of spouted bed. Through CFD-DEM simulations, the effect of six cone angles (28°, 30°, 45°, 60°, 75°, and 90°) on the spouted bed fluid dynamics was also evaluated, in order to determine the configuration that favors the drying process. Smaller cone angles provide better solids circulation with higher mass flow rate, and shorter cycle times. Consistent results were also verified for the heat transfer. After reaching the steady-state, there were no dead zones in the spouted bed, and the particles temperature was homogeneous, which is evidence of the efficient gas-solid contact with this drying equipment.