RESIDENCE TIME DISTRIBUTION IN SCREW EXTRUDERS

A companion article (Chen and Hu, 1993a) discussed a statistical theor y that for a system consisting of two closed subsystems, the residence time density (RTD) functions of the two subsystems will be statistica lly independent, ifa two-dimensional perfect mixing exists at the subs ystem boundary. In this case, the overall RTD function is related to t hat for individual subsystems through the convolution integral. This t heory has been validated experimentally using two die-screw combinatio ns. Based on this theory, a predictive R TD model for an intermeshing counterrotating twin-screw extruder has been developed. The screw in t he longitudinal direction has been treated as C-chambers in series. Th e overall R TD of leakage flows has been calculated from the RTDs of t hese individual chambers and then converted into the RTD of the extrud er. The predicted RTD has been tested against experimental results wit h success.