Study on Fundamentals of Mixing of Powders with Emphasis on Cohesive Systems

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Author Last Name: 
Prof. Dr.-Ing. Karl Sommer, Dipl.-Ing. Volker Kehlenbeck
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Research Area: 
Powder Flow
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Based on the Fokker-Planck-Equation a new model was developed to calculate the reduction of periodic concentration fluctuations entering a continuous mixer. The cal- culations and the experimental results show:

1) The average residence time normalized with the period length of the enter- ing mass flow fluctuations is the main influencing parameter of the mixing quality.

2) The mixing process can be described very well with a system of Fokker- Planck-Equations.

By the development of an air-cleanable cowl for the Near Infrared (NIR) Spectrome- ter VECTOR 22/N it is possible to determine in-line the mixing quality at the end of the continuous mixer every 1.7 sec. The NIR Spectrometer can be used for the analysis of any powder mixture, the only requirement is that the tracer component contains C-H-, O-H- or N-H-groups which absorb the NIR radiation. Because the analysis results can only be as good as the calibration results the calibration was optimised and an apparatus for dust free, easier and faster calibration of the NIR Spectrometer was developed.

For calcium carbonate with an average diameter of 2 μm it could have been shown that the pulsation of a volumetric feeder with a single proportioning device can be reduced tremendously by the use of different dosing tube attachments. The best results were obtained with a self-developed rotating star attachment. The pulsations were reduced to a tenth of the pulsations of a standard dosing tube.