A binary mixture of particles varying in size, shape, or density tends to segregate in many different flow situations. Removal of segregation is an important goal as it is often detrimental to process efficiency and product quality. The focus of the current work is to see the effect of the shape of particles on segregation in the particular case of a fluidized bed solids' mixer. The present work describes an experimental method to study the evolution of segregation and its dependence on both the shape and size of the particles. The outcome shows a decreasing order of the axial segregation index as follows: cubic > spherical > oblate > prolate > elongated needle. An increase in the angularity of fine particles improves mixing. The particle shape plays a vital role in determining the extent of segregation. Overall, segregation can be reduced using nonspherical particles.
The effect of the shape of particles
on mixing and segregation
is studied in a vibrated packed bed mixer. Binary mixtures (unequal
sized) of four types of nonspherical glass particles (cube, prolate,
oblate, and elongated needle) with different aspect ratios are used
alongside spherical particles. The overarching goal is to explore
the effect of the nonsphericity of granules (particles > 2 mm)
used
in the food and pharmaceutical industries. The experimental studies
analyze the mixing behavior based on the particle (shape and size)
and system (frequency and amplitude) parameters. The results show
the existence of a critical vibration intensity (Γ = 4.64) below
which there is little mixing. In addition, the axial segregation index
(SI) value is also significantly correlated to the random monodisperse
packing fraction of coarse particles. The axial SI follows the decreasing
trend: cube > sphere > oblate > prolate > elongated needle.
Similarly,
increasing the fine particles’ angularity from 0 to 0.15, the
axial segregation is reduced from 0.40 to 0.24. The nonsphericity
of particles reveals the tendency to mix more than spherical particles.
These results have important industrial design implications and provide
heuristics to reduce segregation by selecting the particle shape.
The current study aims to investigate the segregation in the dilute phase transport through a pneumatic conveying system. Different types of nonspherical particles such as ellipsoids (prolate and oblate), cube, and elongated needles are mixed with spherical particles to study the influence of nonsphericity. Experiments are performed to examine the effects of particle and system parameters such as particle size, particle shape, gas velocity, and solid loading rate on segregation. A unique decreasing segregation trend is observed for the shape of large particles as oblate > prolate > elongated needle and for the small nonspherical shape as small prolate > small cube. The particle acceleration (drag force per unit mass) is calculated by empirically measuring the average velocity for different particle types. The data shows a correlation between the observed segregation trend and relative particle acceleration for the various particles flowing through the pneumatic conveying system.
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