Characterizing mixing and lubrication in the Bohle Bin blender

Mixing and transport of a cohesive powder are experimentally characterized in a laboratory-scale Bohle Bin blender. The cohesive powder is a blend of Avicel, lactose, and magnesium stearate (MgSt). The effects of vessel fill level, rotational speed, mixing time, and the presence of baffles on mixing are characterized by quantifying MgSt distribution using Near Infrared (NIR) spectroscopy. Results show that the relative standard deviation (RSD) decays faster (on a per revolution basis) and further (lower plateau) at higher rotational speeds. This result indicates a dependence of mixing of cohesive materials on shear. We find that fill level has a strong impact on mixing rate; the higher the fill level, the slower the mixing. Segregated regions are observed at the center of the blender for high fill levels at low rotational speeds. The presence of baffles seems to hinder mixing; the RSD decays are slower and leveled at a higher plateau when baffles are used. Concentration profiles data shows that, at high fill levels, baffles promoted the formation of segregated region at the center of the mixer. (c) 2005 Elsevier B.V. All rights reserved.