Residence Time Distribution in a Single-Screw Extruder Processing Soy-Sweet Potato Mixtures

The influence of feed composition, screw rotation speed and die diameter on residence time distribution of soy-sweet potato samples containing 180 g/kg water and extruded in a single-screw extruder, was measured using congo red as a tracer. Mean residence and plug flow times respectively decreased with starch content. Increase in screw speed enhanced break through time, while a decrease in screw speed enhanced mean residence time. Die diameter had an effect on plug flow time only. The dispersion number, a reciprocal of the Peclet number, was used to describe the extent of axial mixing in the extruder. The value of dispersion number varied from 0.024 to 0.060.