Flow patterns in twin-screw extruders

Abstract Flow visualisation studies in an intermeshing co-rotating twin-screw extruder operated under starve-fed conditions are presented. Different numbers of kneading discs and relative staggering angles were used in the definition of the mixing blocks. Conveying and left-handed elements were also utilised. The images recorded provided information on flow patterns, on the degree of filling of the screw channels and on the number of filled turns. Local flow times were estimated. Partial residence time distribution (RTD) functions were determined by inserting especially designed collecting devices along the barrel, and measuring the evolution with time of the concentration of a tracer.