The residence time distribution curve (RTDC) is largely used to characterize extruder and continuous mixers flow types and on-line measurements allow quick diagnosis of their related problems. The RTDC can be obtained by the single impulse technique, where the tracer is fed into the system at one time and its concentration is estimated at the exit. This paper presents a portable on-line system consisting of a detector which has a light source, an photoelectric cell and a software to collect and analyze the data. Using this system in an intermeshing co-rotating double screw extruder one can verify that the RTDC is much more sensitive to changes of the feeding rate than the screw speed and that the slower tracer fractions may take four times longer than the faster ones to get out. Increase in screw speed and/or reduction in feeding rate increases the axial flow, widening the RTDC.
Residence time; on-line measuring system; light absorption
