Mixer Designs for High Viscosity Materials
Most of the mixer designs for high viscosity mixing equipment have the following characteristics.
- Mixing element operates within all parts of the mixing vessel.
- Low clearances between the mixing element and the mixing container.
- High connected power per unit volume.
- As the forces generated during the mixing process are high, these mixers are rigid in construction.
- The heat evolved during mixing is high. The mixing vessels are therefore provided with external jackets for circulation of cooling media.
- The mixing elements may comprise of intermeshing blades that prevent the material from cylindering along with the rotating mixing element.
- Most mixers are provided with close-clearance blades and / or scraper devices to move stagnant material away from heat-transfer surfaces.
- High viscosity mixers operate at low speeds, require high power and therefore need high torque.
- Discharge of materials after mixing may be difficult and may require special arrangements.
High Viscosity Mixing Equipment
High viscosity mixers can be designed for batch as well as continuous operation. The commonly used high viscosity equipments are as under -
1. Batch Mixers
Single Stirred Mixers
- Anchor Mixer
- Helical Ribbon Mixer
Change Can Mixers
- Banbury Mixers
- High Intensity Mixers
- Roll Mills
Pan Muller Mixers (High Shear Mixers)
2. Continuous Mixers
- Single Screw Extruders
- Twin Screw Extruders
- Pug Mills
Selection of Mixing Equipment
The challenges associated with mixing of high viscosity materials underscores the importance of selection and design of mixing equipment best suited for any given application. Unfortunately, there are many variables in each application and as a result no standard set of rules pinpoints which type of mixer is best suited for an application.
The following are the basic criteria to be considered for the selection of mixers [Tekchandaney, 2012].
- Material characteristics
- Process setup
- Mixer operating parameters
- Mixing accuracy
- Mixer cleanability
- Equipment costs
After short-listing the equipment options, based on the basic criteria; the next step is to test the equipment for the process. Test results can useful data with respect to selection of mixer capacity, power requirements, heat transfer and above all the performance of the mixing process. Selection and scale-up of high viscosity mixers should be carried out in consultation with experts.
- Tekchandaney, J.R. (Author), Holloway, M.D., Nwaoha, C., Onyeweuenyi, O.A. (Editors), (2012), Process Plant Equipment, Wiley.
Paul, E. L., Atiemo-Obeng, V. A., and Kresta, S. M. (Editors), (2004), Handbook of Industrial Mixing, Wiley.
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