Video Analysis Techniques to Visualize Particle-Particle Mixing

Particle-particle mixing has a significant influence on the yield and/or quality of the desired products in numerous industrial processes including energy generation, food processing, and pharmaceutical production. A fundamental problem commonly encountered during the mixing process is the tendency for mixtures to segregate due to differences in particle size, shape, and/or density. Many attempts to characterize the mixing effectiveness of granular applications rely solely on sampling the material after exiting the mixer and it alone does not provide insight into the mixing dynamics during the mixing process. In this study, an optically transparent double screw mixer was used to perform particle-particle mixing visualization studies consisting of a binary mixture of low density and high density granular materials. Four temporally and spatially synced video cameras, as well as optical access around the entire periphery of the double screw mixer, allowed for qualitative observations of the entire mixing process. The effect of four factors on the mixing dynamics was investigated: (i) screw rotation speed, (ii) dimensionless screw pitch, (iii) screw rotation orientation, and (iv) material injection configuration. Dynamic mixing videos and qualitative observations will be presented for a number of different operating conditions, emphasizing the effect these four factors have on the mixing process. The techniques developed in this study provide a thorough method to visualize particle-particle mixing processes and has implications in both batch and continuous systems including fluidized beds, rotating cylinders, screw pyrolyzers, and horizontal impeller mixers.