Mixture and motion of sugar cane bagasse in a rotating drum
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The mixture and motion of fibrous particles of sugar cane bagasse were experimentally investigated in a rotating drum, a configuration frequently used for bioreactors in solid-state fermentation processes. The rotational velocity, filling degree and presence of an inner tube amidst the particles were the controlled variables. The image analysis technique was used to evaluate the radial and axial mixtures. The numbers of rotations used to achieve radial and axial homogeneities were obtained and the radial particle motion described. The minimum numbers of rotations for radial homogeneity were 12, 15 and 17 for filling degrees of 0.3, 0.5 and 0.6, respectively and this number was not influenced by the presence of the inner tube and the rotation velocity. The radial motion was influenced by all the variables and the flow regimes observed were distinct from those previously described in the literature. The passive layer did not behave as a solid body under any of the experimental conditions tested in the absence of the inner tube. When the tube was inserted, stagnant and fast velocities were observed in its vicinity and a porosity profile was noted in the stagnant zone. For both configurations, agglomerates of particles flowed down the free surface rather than a steady flow of particles. The axial diffusion coefficient was experimentally obtained and the simulated tracer concentration presented good agreement with the experimental results.