Analysis of mixing dynamics of powders in conical screw mixer using DEM simulation
Résumé
The conical screw mixer was designed to ensure a high mixing efficiency thanks to the three dimensional flow pattern of particles. The mixing mechanism in the conical screw mixer is predominantly convective, insured by an axial transport by the screw and radial transport, where the screw orbits the conical vessel. However, the operating parameters and the granular properties can affect the quality of mixing. A limited works were devoted to study the mixing dynamics of powders in a conical screw mixer. A recent study of the conical screw mixer using DEM simulation demonstrated that the control of the rotating speed of the screw (axial and radial) leads to an improved mixing rate. In this work we aim to investigate the simulation parameters that influence the mixing criteria. The simulation of a conical screw mixer (5L) was carried out using one million 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 compuational time, the simulation parameters must be chosen carefully. We have investigated the impact of the Young’s modulus and density on the simulation time. We have observed that reducing the Young's modulus could be compensated by a choice of density so it has no impact on the macroscopic mixing dynamics. The simulation was next focused on the investigation of the flow pattern and the velocity profile of particles in a binary mixture with various particle size ratios (1, 1.2, 1.4 and 1.6). The induced size segregation in the mixer is yet to be studied.