Investigation On The Effect Of Blade Patterns On Continuous Solid Mixing Performance

Previous experimental and computational work has demonstrated that the geometry of the impeller has a significant effect on the mixing performance of continuous powder mixers. In particular, different blade patterns using either all blades pushing the powder forward (‘forward pattern’) are less effective than patterns where some of the blades push the powder backwards (‘alternate pattern’). In this article, we use Discrete Element Method to investigate this issue, as well as to examine whether batch mixers can be used to estimate the cross-sectional mixing rate of continuous mixing process. Mixing and flow of particles are examined in simple geometries consisting of a cylindrical cross-section agitated by impellers. In these geometries, blades are designed ‘forward’ and ‘alternate’ to study different blade patterns. Periodic boundary conditions are used to approximate an idealised cross-section of a continuous mixer. In addition, to examine whether an experimentally realisable batch system could be used to validate these cross-sectional simulations, we examine mixing in geometries with solid end walls. Performance in these elemental systems is compared qualitatively in terms of radially averaged velocity vectors, and quantitatively in terms of the mixing rate and the fill level profile. Results show that end walls and symmetric blade pairs of the ‘alternate’ blade patterns lead to faster mixing. Non-symmetric elemental systems display both increased fill level uniformity and similar mixing performance for both blade patterns. Results demonstrate the need for caution when attempting to use batch mixing information to estimate the cross-sectional mixing rate of continuous powder mixers.