RESIDENCE TIME DISTRIBUTION IN KNEADING EXTRUDERS

The residence time distribution (RTD) of a kneading extruder processin g a food material is measured with a lithium tracer. The curve width o f the measured RTD curves is comparable with that of co-rotating, twin -screw extruders. Except for the tail, the extinction curve of the fil led part of the extruder can be described reasonably with a cascade of continuously stirred tank reactors (CSTRs). For the integrated form o f the extinction curve a model which includes a plug-flow in series to the cascade of CSTRs gives a better fit. In the tail of the logarithm ic RTD a divergence can be seen. The use of various RTD models is disc ussed in relation to the measurement.