The single-screw extruder with a perturbation baffle is a novel piece of equipment for polymer processing, in which the polymer melts undergo complex chaotic mixing. In this paper, from a new Lagrangian perspective, the fluid transporting mechanism in chaotic flow of the unwound screw channel was analyzed based on the finite element method. Firstly, two-dimensional velocity distributions in the unwound screw channel were calculated based on the mesh superposition technique. Fluid particle evolution processes in the extruder were tracked based on the fourth-order Runge-Kutta scheme. The numerical method used in this paper was validated by grid independence and experiments obtained from literature. Moreover, the finite-time Lyapunov exponent (FTLE) and Poincaré sections were adopted to discuss the chaotic mixing in the novel single-screw extruder. The effects of baffle width and height on the manifold structures in the flow dynamic system were analyzed. The results show that the homoclinic point of the manifold structure can give rise to chaotic mixing in the single-screw extruder. The height of the baffle is an important parameter to control the chaotic strength. In a way, increasing the height of the baffle can enlarge the kink scale and increase the stretching and folding actions, which results in the decrease of regular regions and an increase of the mixing efficiency in the single-screw extruder.
Funding source: National Natural Science Foundation of China
Award Identifier / Grant number: 51473073
Award Identifier / Grant number: 50903042
Award Identifier / Grant number: 51303075
Funding statement: This work was supported by the National Natural Science Foundation of China (Funder Id: 10.13039/501100001809, grant nos. 51473073, 50903042 and 51303075); the Program for Liaoning Excellent Talents in University (grant no. LR2016022) and the Liaoning Province Natural Science Foundation (grant no. 2015020142).
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