(457a) Wet Flows In a Bladed Mixer: Experiments and Simulations of Monodisperse Spheres
AIChE Annual Meeting
Wednesday, October 19, 2011 - 8:30am to 8:50am
Bladed mixers are commonly used in a variety of pharmaceutical processes such as wet granulation, agitated drying, and mixing and blending. Cohesion due to the presence of a liquid phase is often present in many industrial scenarios where bladed mixers are used (i.e. wet granulation, agitated drying). For bladed mixers, the majority of past studies have focused on dry flows. Therefore bladed mixer processes involving wet flows are not fully understood. The lack of process understanding can lead to operational problems and can cause complications during scale-up.
The flow and agglomeration of wet particles in a bladed mixer was studied experimentally using Particle Image Velocimetry and computationally using the discrete element method. The experimental and computational work showed that particle beds at low moisture contents are characterized by enhanced convective and diffusive particle motion as well as enhanced mixing kinetics when compared to dry particle beds. This behavior is attributed to the development of small particle agglomerates which behave like rough, non-spherical particles and enable the transfer of energy from the blades to the particle bed. At higher moisture contents, a different behavior was observed. Particle convective and diffusive motion was hindered by the presence of moisture at higher levels leading to a decrease in mixing performance. This occurs as large agglomerates are formed and are not broken apart by shear leading to poor mixing. The extent of agglomeration at different moisture contents was quantified via the discrete element simulations. Agglomerate size distributions and morphology were shown to be strong functions of moisture content.