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Characterizing Granular Mixing Homogeneity at Various Dimensionless Mixing Lengths in a Double Screw Mixer

[+] Author Affiliations
Todd A. Kingston, Theodore J. Heindel

Iowa State University, Ames, IA

Paper No. FEDSM2014-21048, pp. V01DT26A001; 8 pages
  • ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels
  • Volume 1D, Symposia: Transport Phenomena in Mixing; Turbulent Flows; Urban Fluid Mechanics; Fluid Dynamic Behavior of Complex Particles; Analysis of Elementary Processes in Dispersed Multiphase Flows; Multiphase Flow With Heat/Mass Transfer in Process Technology; Fluid Mechanics of Aircraft and Rocket Emissions and Their Environmental Impacts; High Performance CFD Computation; Performance of Multiphase Flow Systems; Wind Energy; Uncertainty Quantification in Flow Measurements and Simulations
  • Chicago, Illinois, USA, August 3–7, 2014
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 978-0-7918-4624-7
  • Copyright © 2014 by ASME


Granular mixing processes are commonly used to increase product homogeneity in many industrial applications involving pharmaceuticals, food processing, and energy conversion. Determining the appropriate granular mixing length is necessary to avoid over/under mixing and unnecessary power consumption. The goal of this study is to experimentally characterize the granular mixing process and determine, under various operating conditions, the needed mixing length to achieve adequate mixing in a laboratory-scale double screw mixer. Nine different combinations of screw rotation speeds and dimensionless screw pitches are used to investigate the rate of mixing at dimensionless mixing lengths of L/D = 2, 5, and 10. Composition and statistical analysis methods are employed to assess mixing effectiveness, and it is determined that the dimensionless mixing length is the most influential parameter in terms increasing granular homogeneity. For all the conditions tested, the granular mixture approaches an acceptable level of mixing for all testing conditions when the dimensionless mixing length is L/D = 10. However, the segregation rate throughout the screw mixer is vastly different for various combinations of screw rotation speed and dimensionless screw pitch, and is partly attributed to the influence of entrance effects caused by the material injection process.

Copyright © 2014 by ASME
Topics: Screws



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