Modeling melt conveying and power consumption of conveying elements in co-rotating twin-screw extruders

Abstract Fully intermeshing co-rotating twin-screw extruders are used in various applications ranging from polymer to food processing. Since this extruder type exhibits excellent mixing and sufficient conveying behaviors, it is perfectly suited to use in applications that are demanding in terms of homogeneity, gentle material processing and high product quality. Tailoring the screw configuration and processing conditions to the input material requires accurate prediction of the extruder conveying and power-consumption behaviors. For this purpose, we present novel models of double-flighted fully intermeshing co-rotating conveying elements, which – due to their excellent conveying and pressure build-up capabilities – are the most commonly used elements in co-rotating twin-screw extruders. Our isothermal Newtonian models are based on computational fluid dynamics (CFD) simulation data of the complex element geometry without simplifications, from which we selected a subfactorial dataset of 772 design points that spans a broad parameter range, including various screw pitches, diameter ratios, and screw and barrel clearances. With this dataset as input, symbolic regression generated easy-to-use mathematical functions that incorporate the knowledge gained from the CFD simulations. For the first time, it is therefore possible to predict the conveying and power-consumption behaviors of fully intermeshing co-rotating conveying elements without any simplifications to the geometry and thus with higher accuracy. Our regression models combine the low application barrier of analytical models with the high accuracy of CFD simulations. Inclusion of the screw flight clearances additionally allows significantly improved prediction and understanding of the influences of screw wear on the conveying and power-consumption behaviors and thus on possible material degradation or process changes.