(65c) Analysis of Mixing Dynamics of Powders in a Nauta Mixer Using DEM Simulation

The Nauta mixer was designed to ensure a high mixing efficiency thanks to three dimensional flow pattern of particles. The mixing mechanism in the Nauta is predominantly convective, insured by an axial transport by the screw and a radial transport, where the screw orbits the conical vessel. However, the operating parameters and the granular properties can affect the quality of mixing. Limited works were devoted to the mixing dynamics of powders in a Nauta mixer. A recent study of this mixer using DEM simulation demonstrated that the control of the rotating speed of the screw (axial and radial) leads to improve the mixing rate [1].

In this work, we aim to investigate the simulation parameters (Young’s modulus, friction coefficient and particle size) that influence the mixing dynamics. The simulation of a Nauta mixer (5L) was carried out using one milllion of monodisperse particles (0.9 mm ± 5 % in diameter). Such a large number of particles leads to a high computational demand. In order to save the computational time, the simulation parameters must be chosen carefully. The variation of the Young’s modulus did not show a significant influence on the mixing index. Thus, it was reduced in order to speed up the simulation. The friction coefficient temporarily affects the torque on the screw at the beginning of the mixing operation. The simulation was next focused on the investigation of the particles velocity fields and the induced segregation of a binary mixure with various particle size ratios (1, 1.2, 1.4 and 1.6).

References

[1] Golshan S., Zarghami R., Norouzi H.R., Mostoufi N. Powder Tech. 305, (2017) 279-288