Residence time distribution in twin‐screw extruders

Twin screw extruders are finding increased usage in reacting and devolatilizing applications. Using self‐wiping profiles, the twin screws fulfill the requirement that there be no “dead” or “unmixed” zones. Agitator design must be chosen with care so that a reasonable balance can be obtained between forwarding rate, surface‐generation rate, vapor passageway, power, and axial mixing. Techniques have been developed for measuring residence time distributions and characterizing axial flow behavior. The method also permits direct determination of the holdup in starved barrel applications. Data on residence time distribution are presented for 4‐in. diameter twin screw equipment with a variety of rotor configurations.