Estudo da dinâmica de partículas em tambor rotatório com suspensores: análise experimental e numérica utilizando abordagens euleriana e lagrangeana

Abstract

Rotary dryers are the most commonly used equipment in the granular or particulate material drying, because of their high processing capacity and versatility of operation when compared to other types of dryers. However, the design of these equipment is quite complex, since it involves, in addition to heat and mass transfer, complex fluid-dynamic processes. Therefore, rotary drums with flights, but without the presence of drying air, are generally used for the study of the dynamics of particulate material in these dryers. When the drum is in the ideal loading configuration, there is the greater interaction between the particulate material and the flowing air, which is interesting in a case of drying. Based on this, in this work a rotating drum with variable number of flights was built, aiming at the study of the rotary drum in the ideal loading condition. In this way, applications of geometric models for the prediction of this condition were studied and the ideal rotation speed of the drum was determined for different operating conditions of the equipment. This study determined a model for predicting the ideal Froude number as a function of the drum filling fraction, number of flights and material properties, such as density, static angle of repose and dynamic friction coefficient of the material. Besides these, studies were also carried out regarding the angle of last discharge, evaluating the effects of the operational conditions on the discharge of solids in the drum. As a complementary tool to the experimental studies, numerical simulations help the understanding of the flow of granular materials. Regarding the numerical approach, two different approaches for predicting the granular flow inside the drum with flights were used: Eulerian and Lagrangean. In the development of an Eulerian model, using Computational Fluid Dynamics (CFD), it was possible to determine the boundary conditions and to find the best model to reproduce the experimental results, in which the application of the model of turbulence k-ɛ was essential in the description of particle dynamics. In the simulations using the Lagrangian approach (through the Discrete Element Method (DEM)), parameters related to the properties of the particles, such as Poisson Ratio and Shear Modulus, were investigated, as well as particle-particle and particle-wall interactions through coefficients of restitution and static and rolling friction. In this work, a set of parameters was found through which the simulation represented the experimental data well. In addition, it was observed that the use of a smaller shear modulus than the actual one to decrease the computational cost was a valid assumption, mainly for lower rotation speeds. Comparing the two methodologies, it was possible to find the advantages and disadvantages of each one of them. The lagrangean approach allowed to observe each particle individually, being possible the determination of the length of fall of the particles. However, with the change in operating conditions, such as the number of flights, the results presented by the Eulerian approach were better.