Mixing and motion of rice particles in a rotating drum

The mixing and motion of particles were analyzed in a rotary drum as part of the development of a solid-state fermentation bioreactor for spore production from the fungus Metarhizium anisopliae. Rice was chosen as the particle because it is often used as a substrate for fungal incubation. The controlled variables were the particle load, drum spin velocity and the presence of inner tubes. The dyed-tracer technique was applied to the system, and image analysis was performed using the commercial software LensEye. A detailed calibration procedure is described. The software was able to identify particle weight concentrations of up to 20% with good accuracy. The load of particles was the only variable to influence the number of revolutions necessary to obtain a uniform mixture: 5, 9 and 11 rotations were required to homogenize 5, 10 and 15 kg of particles, respectively. The presence of inner tubes strongly influenced the particle velocities in the central core of the bed and changed the velocity patterns in all regions.

Graphical abstractThis work assessed the mixture and the velocity distribution for particles of rice in a rotating drum. Bed load was 5, 10 and 15 kg and drum rotation 1, 4 and 7 rpm. Experiments were carried out with and without submerged tubes. Mixture was dependent only on the bed load. Five zones of different velocities were observed for experiments with submerged tubes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► This work addresses particle mixing and motion in a rotary drum filled with rice. ► Drum rotation, particle load and the presence of submersed tubes were variables. ► Homogeneity was achieved after 5, 9 and 11 revolutions for loads of 5, 10 and 15 kg. ► Homogeneity was independent of the rotational velocity and the presence of the tubes. ► Five zones of different velocities were observed for experiments with submerged tubes.