Experimental Methods for Determining Mixing Quality and Residence Time Distribution

2 Experimental Methods for Determining Mixing Quality and Residence Time Distribution 

One method of determining the mixing quality is to use optical evaluation. A suitable set-up is shown in Fig. 9.19. Here, the main stream being fed to the extruder is a clear oil. A side stream containing a tracer is introduced at some arbitrary position along the screw. This approach allows the length available for mixing to be varied. The extruder can be equipped 

For a quantitative evaluation, the gray scale values are recorded along an imaginary line and the tracer concentration is then calculated from these values. The number of individual concentration values that can be evaluated, i. e., the number of individual samples, is limited by the resolution of the camera. Usually, the number of individual samples is matched to the number required in production. This may, for instance, be the number of strands in pelletizing. 

in addition, the barrel of the trial machine is manufactured from a transparent material (Fig. 9.20), the mixing behavior in the machine can be observed first-hand. This provides valuable information about the mixing performance of a screw configuration. 

With the aid of the experimental techniques that have been briefly described here, the mixing performance of screws can be investigated with relatively little effort. Such investigations are useful, for instance, when developing new screw elements and optimizing screw configurations. With the proper equipment, it is also possible to investigate dispersion processes. 

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