Using DEM, the evolution of the central core during mixing of particles is shown. The results obtained from the numerical and experimental work illustrate that for mixing of binary mixtures of same size particulate solids, the geometric structure of central core at the axis of rotation depends upon the packing arrangement of particles inside the drum. The central core forms when the drum is filled above 50% and its size increases with increase in the filling of the drum. With increase in drum speed, the size of the core shrinks. Radial segregation and axial segregation of particulate solids always occur in rotating drums. Even a small size variation may lead to segregation. The radial segregation was found to be complete within two revolutions, whereas axial segregation was not detectable during the same time period. Thus, it is believed that the radial segregation is faster than the axial segregation.
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