Rotor-Stator Mixers for High-Speed Mixing
Key Takeaways
Rotor-stator mixers are high-shear mixers that are used as standard tools for the emulsification and mixing of fluids.
For mixing samples with high viscosity, rotor-stator mixers are preferred.
Rotor-stator mixers are employed in the biochemical, cosmetic, chemical, agricultural, and food processing industries.
Rotor-stator mixers are used in the food, pharmaceutical, chemical, and polymer industries, to name a few.
Breaking down agglomerates into smaller particles is a common process in most industries. Industries often rely on rotor-stator mixers to quickly reduce the size of samples. Rotor-stator mixers are necessary for industries requiring high-speed dispersions.
Let’s dive into fluid mixing using rotor-stator mixers.
Mixing Fluids
Mixing various fluids is essential in the food, pharmaceutical, chemical, and polymer industries. Fluids are mixed to prepare emulsions, dispersions, etc. The flow regimes in the mixing process can be laminar or turbulent. Depending on the production process, mixing can be either a continuous process or a batch mode process.
Conventional Mixing Processes
Previous mixing processes involved stirring actions in the fluid contained in a vessel. The process of mixing was predominantly manual, and in certain cases, used conventional mechanical stirred vessels with impellers. Generally, conventional mixing methods resulted in inefficient mixing processes.
The mixing process and the results differ depending on the fluid type. The viscosity of the fluid is an important factor in determining the type of mixer and mixing method to be used.
Non-Newtonian Fluid Mixing
Non-Newtonian fluids are characterized by high viscosity and therefore the mixing of such fluids is usually performed under the laminar flow regime. However, the laminar flow regime is not efficient in the mixing process, as fluid flow is predominantly developed by viscous force.
Poor mixing results due to the formation of well-mixed regions and dead zones. Well-mixed regions are regions where the mixing is proper and particle size reduction or stable dispersion takes place. Dead zones are regions where the mixing process is not effective or not even there.
In order to provide good-quality mixing, rotor-stator mixers are used in a variety of industries. Compared to conventional mixing methods, rotor-stator mixers ensure the creation of flow or shear rates in a large part of the fluid and provide a nearly ideal mixing process. High-speed mixing is possible with rotor-stator mixers.
High-Speed Mixing
High-speed mixing is commonly used to mix solids into liquids. High-speed mixing becomes inevitable when the mixing involves large amounts of solids or powders that start to wet out. High-speed mixing incorporates both high shear and turbulent conditions in the fluid flow. High-speed mixing is ideal for emulsification, particle size reduction, and homogenization. Most industries use rotor-stator mixers to accomplish high-speed mixing.
Rotor-Stator Mixers
Rotor-stator mixers are high-shear mixers that are used as standard tools for the emulsification and mixing of fluids. In rotor-stator mixers, the rotor runs at a high speed and acts as a centrifugal pump, drawing the materials from above and below, which breaks the samples into smaller particle sizes. High-pressure homogenizers also perform mixing and emulsification. However, they are best for low to intermediate-viscosity fluids. For mixing samples with high viscosity, rotor-stator mixers are preferred.
Compared to high-pressure homogenizers, rotor-stator mixers can be operated in two modes:
Continuous mode - Also called an inline rotor-stator system. The process is continuous.
Batch mode - Rotor-stator mixer operation is discontinuous. The batch mode operation of the rotor-stator mixer differs from the continuous mode operation in terms of pumping power, shaft power, efficiency, and product quality.
Construction
Rotor-stator mixers consist of a set of rotors and a set of stators. The rotors rotate at high speed in the vicinity surrounded by the stationary stators. The rotor tip speed is usually in the range above 10 m/sec, with the rotor and stator gap ranging above 100m. The design of the rotor-stator mixer is made so that it develops high shear stress and high intensity of turbulence. The rotor generates energy, which gets dissipated inside the stator. This kind of energy dissipation leads to high local energy dissipation in rotor-stator mixers compared to conventional mechanically stressed vessels.
Characteristics
The characteristics of rotor-stator mixers are:
- High-shear
- High-power
- High-speed
Rotor-stator mixers generate the energy for mixing fluids or samples, shear stress, elongation stress, and turbulence cavitation, which provides particle size reduction and mixing.
Applications
Rotor-stator mixers are employed in the biochemical, cosmetic, chemical, agricultural, and food processing industries. The application process of a rotor-stator mixer involves operations such as dispersion, emulsification, homogenization, grinding dissolving, chemical reaction, cell disruption, and coagulation.
Study Shearing Effects in Rotor-Stator Mixers With Cadence Tools
Cadence offers a CFD platform to support the study of the turbulence and shearing effects in rotor-stator mixers.
Subscribe to our newsletter for the latest CFD updates or browse Cadence’s suite of CFD software, including Fidelity and Fidelity Pointwise, to learn more about how Cadence has the solution for you.