Automated design and optimisation of dynamic mixing and shear elements for single-screw extruder

• Applicants: Professorin Dr.-Ing. Stefanie Elgeti; Professor Dr.-Ing. Christian Hopmann
• Subject Area: Plastics Engineering
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 327074219

Mixing and shear elements are increasingly used in single-screw extruders due to the demand for ever higher throughputs while maintaining plastics melt homogeneity. The task of mixing and shear elements is to disperse and distribute additives and fillers evenly in the plastics melt and homogenise the melt thermally. To date, the design of mixing elements is based on the experience of the designer. By contrast, a much more detailed insight into the mixing process can be achieved via three-dimensional simulations. However, available approaches for the computation of mixing operations in extruders often have great limitations and are generally used only for exemplary evaluation of individual mixing elements. Difficulties arise on the one hand in the choice of a suitable mixing index. On the other hand, the high effort in the numerical optimisation of mixing elements is an obstacle to the use of flow simulations in the design phase. So far, there is no software for the automated optimisation of mixing elements available.Against this background, it is the goal of this project to develop an optimisation framework that enables the automated simulative design and optimisation of mixing and shear elements in single-screw extruders. With this framework knowledge about the ideal mixing element geometry in dependence of the mixing task will be acquired. For this purpose, the existing in-house flow solver of the applicant CATS will be modified in order to enable the non-isothermal simulation of the mixing processes in the melt zone of the extruder. The modified solver will then be integrated into an optimisation routine. Meanwhile, the IKV will identify suitable boundary conditions for a realistic three-dimensional simulation of complex mixing elements using a comparison of simulation results and experimental reference data. In the next step, the IKV will simulatively compare different mixing indexes and identify those indexes that are particularly well suited for the design of mixing elements. These mixing indexes are combined into a single objective function in the optimisation framework. In addition, the IKV will simulatively analyse and characterise the cause-effect relationships between the mixing element geometry and the resulting flow conditions. This gain in knowledge will be incorporated into the optimisation framework and facilitate the identification of suitable mixing element sections that will be enabled for the optimisation. Following its successful implementation, the optimisation framework will be used by IKV and CATS in order to design and optimise a mixing element sequence, which is suitable for a very wide range of applications. Thedeveloped mixing element sequence will finally be manufactured and used for the practical validation of the optimisation framework.

• DFG Programme: Research Grants