The role of boundary conditions on the dynamics of green coffee beans in a rotated dryer

Coffee drying and roasting are usually performed in rotated dryers; therefore, the study of particle dynamics in this equipment is of great relevance to improve their efficiency and hence the quality of the final product. Thus, this work aimed to investigate experimentally and numerically the dynamics of coffee beans in a rotary dryer. The Euler-Euler model was employed to reproduce the particle velocity profile in the rolling regime under different boundary conditions. The results shown that the lower specularity coefficient (0.01), which characterizes the smooth wall and free slip condition, reproduced the bed behavior that most resembled the experimental one. On the other hand, the other coefficients (0.1 and 1.0) showed an increasing deformation in the bed surface, different from the observed experimental behavior. It was also verified that, as the filling degree increases, the bed surface deformation becomes more pronounced. Keywords: coffee; rotated dryer; simulation; specularity coefficient.