A design heuristic for optimizing segregation avoidance practices in horizontal drum mixers

• Segregation can be thwarted by flow inversion.
• The effectiveness of this technique is related to the layer pass frequency.
• A design heuristic can be based on the probability distribution of this frequency.

Segregation is a major problem for many solid processing industries. Differences in particle size or density lead to flow-induced segregation within the surface layer. Here we examine methods of avoiding radial segregation in a horizontal drum mixer. Recently, it has been suggested that segregation in this type of particle mixer can be thwarted if the sheared (surface) regions of the bed are inverted at a rate above some critical frequency. Further, it has been hypothesized that the effectiveness of this technique can be linked to the probability distribution of the number of surface layer “passes” a particle takes per rotation of the drum. In this article, various baffle configurations are numerically and experimentally studied to investigate the efficacy of this measure as a design heuristic for the development of improved drum mixing devices. We choose the horizontal drum geometry as it represents the simplest possible example of a tumbler-type mixer, however, we expect the results found here regarding the efficacy of our design heuristic to be generic for any surface-dominated mixing device.

Fig. 1: Images showing qualitative comparison between experiments and DEM simulations of the asymptotic state of mixing in rotating tumblers with various novel baffle configurations. An unbaffled case (top) has also been shown for comparison. The emphasis here is on different kinds of baffle placements within the tumbler. Two different sized particles are considered: 2 and 3 mm acetate beads. The effective length of the baffles is fixed and the cylinder is rotated at 6 RPM.Figure optionsDownload as PowerPoint slide