THEORETICAL TOOL FOR OPTIMUM DESIGN OF MIXER, AND VISUALIZATION AND QUANTIFICATION OF MIXING PERFORMANCE

A theoretical tool for the optimum design of a mixer, and visualizatio n and quantification of mixing performance, is presented. Visualizatio n of the mixing performance is based on the kinematic theory of mixing rate proposed by Ottino, and it gives a map of the distribution of lo cal mixing efficiency which illustrates the local mixing information t hroughout the flow domains. As application examples of the visualizati on technique, the mixing mechanisms of Couette flow and circulating fl ow are illustrated and explained, then the geometry optimization of a common pin mixing section used for screw extruders is carried out. The quantification of mixing performance is obtained by tracking and accu mulating the local mixing histories of a number of particles to discri minate the mixing ability among several mixers with similar configurat ions. The influence of the height of a pin in a cavity on mixing is in vestigated using this approach. The results show that with an increase in the height of the pins, the mixing ability also increases, However , when h changes from 3/4H to 9/10H, an inflection occurs. The results also show that only if these particles are evenly distributed through out the now domains will the calculated values of mixing ability in di fferent initial locations start to agree. This tool appears to be gene rally applicable to mixers but requires knowledge of the velocity fiel d.