Characterization of granular mixing in a helical ribbon blade blender

• Mixtures of different size distribution materials were investigated by sampling.
• Experimental mixing states and torque-on-blade in an agitated mixer were studied.
• High mixing homogeneities were achieved fast and stable for a range of parameters.
• Reported experimental results are a useful basis for validation of DEM simulations.

Experiments of bulk solid mixing in a twin ribbon blade blender have been performed in this work in order to characterize mixing behavior in such a mixer for binary mixtures with different cohesionless materials. The effects of fill height and blade rotation speed on mixing homogeneity have been studied. Mixing homogeneity was determined by sampling. It has been observed that mixing is relatively fast towards a final mixing state within approximately 100 blade rotations for different combinations of material, fill height and blade rotational speed. Moreover, these final mixing states seemed stable within a range of fluctuations, which may prove useful in determining an optimal mixing time for binary, cohesionless particle mixtures and potentially lead to a reduction in the required number of blade rotations in mixers of this type in industry. Mixing homogeneity results indicated an increased final mixing homogeneity for increasing fill height, most clearly in the range of 30–70 vol.% in the studied twin ribbon blade mixer. The torque on one of the shafts was determined. The latter results showed that no significant influence of rotational speed on the required torque for the tested mixtures at rotational velocities in the range of Fr 0.17–1.1 could be determined for most combinations of the tested materials and fill heights in this work. The quantitative characterization of mixing behavior with the two key parameters mixing homogeneity and torque on the shaft may be used for mixer validation of DEM simulations.

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