Dimensional analysis of a planetary mixer for homogenizing of free flowing powders: Mixing time and power consumption

Abstract

Powder mixing is crucial to the processing stages in many industries. However, there is still a paucity of information about the effects of process parameters on mixing efficiency. This paper investigates the homogenization of free flowing granular materials with a planetary mixer, TRIAXE®, examining the effect of the ratio of impeller rotational speeds (NR/NG) on the mixing process.First, a dimensional analysis carried out with mixing time and power consumption as target variables, established that both a Froude number and NR/NG controlled the process for the given free flowing powder mixture and planetary mixer.A further theoretical approach also suggested that these two dimensionless ratios which control hydrodynamics can be reduced to a modified Froude number providing that the maximum linear velocity achieved (uch) by the planetary mixer is introduced, replacing the dual impeller rotational speeds (NR and NG).Mixing time and power experiments validated the above hypothesis. Homogeneity tests performed in a granular media showed that the length of path achieved by the impeller governs the obtained mixing level.Finally, this work reflected that (i) dimensional analysis was also well suited to model powder homogenization with a planetary mixer. (ii) A concise set of dimensionless numbers governing mixing phenomena can be deduced through the introduction of the maximum linear velocity as obtained in previous studies on gas/liquid and miscible liquids mixing processes.