(303c) Low Shear Continuous Tumble Mixing Characterization
In this decade the study of flow and mixing of granular materials has increased exponentially compared to the last decades. The advance has been noticeable in both the computational and the experimental studies especially in batch systems. However, due to the Process Analytical Technology (PAT) initiative, special attention has been focused on continuous systems due to the ability to control instabilities on line making processes more efficient. In this work, a new continuous low shear mixing device consisting of two, short, acrylic, hollow concentric cylinders was developed to study granular mixing. The inside cylinder has multiple orifices of 2 mm of diameter and the complete mixer moves counter clockwise making powders to form an avalanche while at the same time powders escape from the inside cylinder to the outside cylinder by the help of centrifuge forces. Mixed powders are collected in the outside cylinder and analyzed to obtain the degree of mixing achieved. The goal is to develop a macro understanding of a low shear continuous mixing device, create low order models to describe the relationship between mixing performance and the operating conditions, and to understand the effect of material properties on residence time distribution and homogeneity of output stream. Results demonstrated that mixing is highly affected by the feeding rate and the RPMs of the tumble. Powder properties such as the cohesion of the mixture and particle size distribution affect considerably the hold up and the average residence time. Effects of lubricants such as Magnesium Stearate affect the dynamic behavior of powders inside the mixer and the mixing as well.