Evaluation of Change-Can Mixer Designs Via CFD Modeling

Change-can mixers are commonly used for processing high viscosity fluids at industrial scale due to their versatility. Multiple low and high shear blades that are independently driven and controlled can be used in mixing tank which makes it ideal for multitasking, to streamline processing operations and lower production costs. In order to obtain the desired properties, key process parameters require careful control, such as shearing intensity and mixing time. Predicting the mixing performance, such as mixing time, shear rate and fluid velocity, remains of key importance in process control, and it is the only way to ensure a high quality and uniform product.

To have a better understanding of the mixing impact of change-can mixers for producing stable mixtures, this study investigates the liquid-liquid mixing efficiency of different change-can mixer designs using the same impeller and disperser blade type. Computational fluid dynamics (CFD) modeling can provide detailed information about hydrodynamics and mixing. However, it is computationally intensive, especially multiphase transient simulations. Therefore, in this work, to reduce time and computational expense, the rotation of the blades in the change-can was modeled using the steady state multiple reference frames (MRF) technique with k–ɛ model. Subsequently, the mixing time analysis was calculated by the transient species transport model using fully developed flow field with commercial code Ansys Fluent 16.2.

Water and glycerin mixing was used for a case study. Three-dimensional (3D) simulations of mixers were created and compared: 1) the blades rotate at fixed positions, 2) the blades rotate at a planetary motion and 3) a spiral ribbon addition on the fixed blade. Simulations show faster mixing time with glycerin on top compared to water on top, and significant time improvement with a spiral ribbon addition on the fixed blade. In conclusion, a less expansive spiral ribbon addition on the fixed blade is more efficient as compared to a more expensive investment involving blades rotating in planetary motion.