Rotor-stator mixers provide high deformation rates to a relatively limited volume, resulting in a region in which intensive mixing, milling, and/or dispersion/emulsification operations can occur. Because they are geometrically complex, experimental measurement of important flow regions within rotor-stator mixers is often difficult, if not impossible. Computational fluid dynamics (CFD) simulations of mixers are a means to provide flow data that are of benefit to both designers and end users.
This presentation focuses on our recent work in the fully transient (sliding mesh) three-dimensional RANS simulation of a pipeline rotor-stator mixer, the Greerco High Shear Pipeline Mixer, using ANSYS FLUENT. The modeled unit consists of two conical rotor-stator stages, each with a nominal diameter of 4 inches, aligned to produce an axial discharge flow. The realizable k-ε model was used to model turbulence, while wall effects were modelled with enhanced wall treatment. The mixer geometry consists largely of cylindrical and conical bodies; the impact of this on meshing will be discussed. The working fluid was water in turbulent flow.
With a relatively coarse mesh, the predictions of throughput by the FLUENT simulation matched the measured values provided in the Greerco Pipeline Mixer literature. However, a greater mesh density is required to resolve the velocity fields. The effect of mesh density is illustrated by comparing selected velocity profiles. The mesh-independent solution is used to show various flow field features. As with other rotor-stator mixers, fluid is shown to impinge on the trailing surface of the stator slot. In addition, it is shown that the conical shape of the rotor and stator causes flow rates through the outer regions (where the rotor tip speed is higher) to be much higher than at the inner regions. In the case of the second stage stator, very little flow enters the inner two rows of slots. The effect of the flow field predictions on various aspects of device performance will be discussed.