Experimental and numerical investigation of mixing and segregation of free-flowing and cohesive powders in GEA Gallay tote blenders.

摘要

This dissertation presents a systematic study (experiments and computer simulation) performed to investigate the degree of mixing and segregation of free flowing grains and cohesive powders in the GEA Gallay tote blender as a function of various process parameters. Validated sampling and analysis techniques are employed to quantify the homogeneity of the final mixture by calculating the RSD (relative standard deviation), a mixing index commonly used as a measure of mixing performance.; The rate of mixing of the similar size and shape free flowing material is significantly dependent on fill level, mixing time, and initial loading pattern. On the other hand, the homogeneity of the final mixture is independent of blender rotational speed and blender discharge. The optimum fill level is 60% of the total blender volume, and the manufacturer's prism baffle slightly improves mixing. Like other blenders, the mixing rate in the radial direction is at least an order of magnitude greater than in the axial direction.; The homogeneity of the cohesive powder system is a function of fill level, initial active aggregate size, and high shear pre-blending (only for initially small aggregate sizes). Unlike the free flowing case, the mixing of the cohesive formulation is largely insensitive to mixing time and active concentration, and dependent on vessel rotational speed and blender discharge. The homogeneity of fine powders similar in size and shape improves upon discharge, however the dependence on speed is complex and currently not understood.; The particle dynamics simulation confirmed the experimentally observed dependence of mixing on fill level, loading pattern, and particle movements in the GEA Gally tote blender. Good agreement was obtained between the degree of mixing of the simulation and the experiments for axial mixing, and radial mixing at longer times (above 7 revolutions). Incorporation of rolling friction in the simulation is recommended to enhance the prediction of the degree of radial mixing at short times. The difference between the simulation's rate of segregation and that of the experiments as the fill level is increased is not yet understood and is a topic for future work.