Effect of blade angle and particle size on powder mixing performance in a rectangular box

a r t i c l e i n f o Keywords: Mixing performance DEM MGMMI Blade-rake angle Bladed mixers This study focuses on the understanding of flow over a single blade and its impact on powder mixing. The Discrete or Distinct Element Method (DEM) is used and the flow of a single blade through a bed of a binary particle mixture is studied. Mixing performance with respect to a blade-rake angle and particle size is investigated using the Modified Generalized Mean Mixing Index (MGMMI) and the maximum mean instantaneous velocities. A wide range of angles and different loading scenarios of the binary particle mixture were studied. Velocity profiles for all these cases were computed, as well as the forces on particles and the blade. The results showed an inverse relation between the interparticle force and blade-rake angle. Systems with a higher number of larger particles experienced a higher interparticle force. Similar results were obtained for the blade force. The results for mixing efficiency showed that if the smaller particles are placed at the top this leads to a higher mixing performance. The mixing performance was highest for blade-rake angles that offered a maximal surface area or maximal resistance to the flow of particles, which occurred for blade-rake angles from 70° to 90°. A wide variety of industrial mixers (blenders) are employed for solid particle (granular) mixing, particularly in the pharmaceutical industry due to the need to blend small quantities of active pharmaceutical ingredients (APIs) with larger amounts of excipients to provide the final mixture for a pharmaceutical dosage form. Clearly, blending is a key unit operation for solid dosage form manufacturing as it ensures blend homogeneity that is directly linked to the (potential) critical quality attribute (CQA) " content uniformity " , which in turn is directly related to product safety and efficacy [1]. Inefficient blending can lead to increased variability of the active component in the final dosage form, threatening the health of patients [2]. Thus, the understanding of granular mixing or powder blending has been a focus of interest for many decades. A general classification of mixing mechanism has been given by Lacey [3]. Shear mixing can occur in convective, high-shear mixers and tumbling mixers, where a layer of powder avalanches down along a slope plane [4]. Convective and shear mixing are difficult to distinguish [5] in dense particle systems and can be collectively termed as convective-shear …