Measurement of velocity profiles in reverse‐screw elements of a twin‐screw extruder

A laser Doppler anemometer was used to measure velocity components for the flow of a Newtonian fluid in a reversing section of a pilot‐scale corotating twin‐screw extruder. Measurements were made at a fixed axial position in the intermeshing (nip) region and the translational region (áway from the nip). Tangential and axial velocity profiles reached a maximum in the middle of the screw channel, indicating pressure flow. Leakage flow through the gaps between screw flights and backflow toward the hopper were observed only in the nip region. No reversal of flow was detected in the translational region. Measured velocity profiles showed substantially higher shear rates in the reversing section of the screw as compared to those in the forward‐conveying section.