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theses

Mixing is used in various processes across the industry and is an important operation to control the quality of products in particle processes. Rotary blenders are widely used for the mixing and dry impregnation operations and it has been understood from previous research that in such blenders the time scales for axial mixing were significantly larger than for radial mixing. The goals of this work are to understand how baffles affect the mixing process in a rotating vessel and to develop a method to determine the optimum baffle size and position to be used in a double cone vessel. To increase the extent of axial mixing, baffles that break the line of symmetry along the axis (three along the cylindrical section and two along the conical sections of the double cone) were considered. In this work we use Discrete Element Method (DEM) simulations to study systematically the effect of baffles on the axial mixing and dry impregnation in the double cone blender. The effect of different properties of baffles, e.g. height, position, angle of orientation of baffles with the various process parameters, e.g. fill level, particle size, rotation speed on the mixing performance were studied. To measure the degree of mixing we use the Kramer mixing index, which is based on the distance between the volume centers of an axially segregated system, was calculated to quantify the mixing of the system. Simulation results show that there is an optimal baffle height for low fill levels, beyond which the mixing performance declines. The angle of orientation has little to no effect on mixing performance for large particles, whereas for smaller particles, there is an optimum range of operation. Also, results for the baffle position indicated that it affects mixing significantly more at lower fill levels, and an optimum baffle position could be found. We determined the positions in the double cone for which the particle velocity is maximum. Our proposed hypothesis is that if the baffles are located in the position of maximum velocity, they will tend to break the flow and offer best mixing performance. We observe that baffles considerably increase homogeneity in the impregnation process, but we do not observe significant differences between mixing performance for different baffle positions.

ETD_9340

M.S.

Includes bibliographical references

by Aman Rastogi

doi:10.7282/t3-8zcj-pj04

ETD graduate

The author owns the copyright to this work.