Regime changes of industrial powder mixing in a stirred vessel

Granular mixing was investigated as a representative of powder mixing in a stirred vessel using the discrete element method. A wide variety of changes in relevant parameters were examined, which revealed four distinct mixing modes: bulk rotation, shear band-driven mixing, fluidized mixing, and fluidized mixing with a vertical split. Based on dimensional analyses and physical arguments, the transitions in mixing modes were described using four dimensionless variables: the friction coefficient, dimensionless height, Froude number, and dimensionless elastic modulus. The friction coefficient was seen to have an important role in determining the mixing mode as well as dimensionless height. The regime plots for mixing modes were then constructed in the two-dimensional friction coefficient–dimensionless height space for a given Froude number and dimensionless elastic modulus. To the best of the author's knowledge, this study is the first to unveil the regime changes of granular mixing in a stirred vessel; therefore this study will improve the physical understanding of this problem and provide practical guidelines for designing powder mixing for industrial applications.