CFD Investigations of Industrial Mixing in the Transition Region

Mixing is commonly performed in the manufacturing and processing industry. To optimize the mixing efficiency, understanding the process details inside the tank is a crucial step. Industrial mixing is typically studied and modeled in the laminar or turbulent regimes, as the equations governing these regimes are well understood. Due to the complexity of transition mixing, there has been minimal modeling done despite transition mixing being a common working regime for many industrial processes. The lack of accurate transition mixing models hinders industries in optimizing their processes and inhibits the investigation on the behavior of the transition regime.

Computational Fluid Dynamics (CFD) simulations are used to analyze the properties and behaviors of fluid domains within a mixing tank. ANSYS Fluent, a commercial CFD software package, is used in modeling various physical systems to analyze velocity profiles, streamlines, volume fraction distribution, and numerous other fluid and flow properties. The goals of this research are to investigate the behavior of a non-Newtonian Carbopol being mixed in the transition flow regime using CFD, and to adapt these computer-generated models to physical systems to increase the accuracy of the transition mixing models. The viscosity of a non-Newtonian fluid depends on shear rate, which results in different Reynolds numbers throughout a tank, since the Reynolds number is a function of viscosity.

Three different Reynolds numbers within the transition regime were modeled: 124, 271/297, and 530. Two sets of models were generated, each with the Reynolds numbers listed previously: (i) with changing impeller speed and (ii) with changing viscosity profile. This also allows for an investigation on the flow field’s behavior with changing viscosity versus changing impeller speed despite having the same Reynolds number. Using data from actual mixing systems, models of the systems were generated, analyzed, and modified using ANSYS Fluent to accurately represent the physical systems. Data in the form of pictures, videos, and torque readings will be used to compare the real system to the models. This investigation will lead to more accurate transition mixing models, a better understanding of the effect of different variables on flow domains with the same Reynolds number, as well as a deeper understanding of the transition regime.