Modeling residence time distribution in a twin-screw extruder as a series of ideal steady-state flow reactors

Knowledge about and control of residence time distribution (RTD) is critical for determining optimal conditions in an extrusion process. In this paper, previously proposed models for RTD have been summarized and compared with the experimental data. The best-fit model was found to be a plug flow in series with a finite number of constantly stirred tank reactors having dead volume fractions. Parameters of the best-fit model were predicted from input variables (moisture content, screw speed, nozzle diameter and barrel temperature). Predicted RTD from the input variables had a r2 > 0.96. Experiments were conducted using a full factorial design with moisture contents of 16, 20, 24 and 28% (wb); screw speeds of 80, 120 and 160 rpm; nozzle diameters of 3, 4 and 5 mm; and barrel temperatures of 120 and 140 °C. Each experiment was replicated twice. It was found that, within the range of conditions studied, moisture content, screw speed, barrel temperature and nozzle diameter had significant effects on RTD.