Particle Mixing Measures in a Vertical Bladed Mixer Using X-Ray Computed Tomography (CT)

Vertically bladed mixers are widely used in various solids-handling industries such as cosmetics, food, and pharmaceutical manufacturing. Difference in the particle size, particle density and volume fraction of the different species in a binary mixture can affect the location and velocity profiles of these particles. These effects in turn, influence the time scales and behavior of the mixing/segregation process. In this study, mixing of binary mixtures was investigated in a bench scale vertically bladed mixer fitted with two 45^o blades. Wood and Delrin® particles of different sizes, masses and in different volume fractions were used to experimentally simulate the effects of these parameters on the mixing/segregation process of the binary mixture.

X-ray computed tomography (CT) was performed on the bladed mixer to determine the 3D location of all particles in the mixer. Since X-rays are attenuated differently by materials of different densities, the different constituents in the binary mixture can be easily distinguished in the CT reconstructions. The dispersion of the two species in different regions of the mixer vessel at different mixing times was investigated and was used to provide an accurate representation of the mixing/segregation process. The magnitude of mixing was quantified using Lacey’s Index [1], a particle scale mixing index (PSMI) [2] and a grid-independent segregation index [3].

References

[1] P.M.C. Lacey, The mixing of solid particles, Chem. Eng. Res. Des. 75 Supplem (1997) S49–S55.

[2] G.R. Chandratilleke, A.B. Yu, K. Shinohara, A particle-scale index in the quantification of mixing of particles, AIChE J. 58 (2012) 1099–1118.

[3] M.S. Siraj, S. Radl, B.J. Glasser, J.G. Khinast, Effect of blade angle and particle size on powder mixing performance in a rectangular box, Powder Technol. 211 (2011) 100–113.