Analysis of Mixing Mechanism in Eccentric Twin⁃screws Extruders Based on Lagrangian Method

doi:10.19491/j.issn.1001-9278.2020.08.009

Abstract

Abstract:

The mixing characteristics in the flow field of three eccentric twin?screw extruders with the eccentricities of 4 mm, 2 mm and 0 mm were comparatively investigated by use of a finite?time Lyapunov exponent (FTLE) and a Lagrangian coherent structure (LCS) combined with the mixing index and instantaneous mixing efficiency. The results indicated that when the eccentricity was 4mm, the fluid particles had a traversal range in the eccentric twin?screw extruder, and their Lagrangian coherent structure was relatively complete. There were some hyperbolic fixed points in the flow field, and the fluid particles underwent relatively good stretching and compressing actions. The analysis of instantaneous mixing efficiency parameters revealed that the mixing efficiency of the eccentric twin?screw extruder with an eccentricity of 4 mm was superior to the other two models.

Key words: twin screw extruder, lagrangian coherent structure, finite?time Lyapunov exponent, mixing index, instantaneous mixing efficiency

CLC Number:

TQ 320.5⁺2

Jian TENG, Dongyang WANG, Xiangzhe ZHU. Analysis of Mixing Mechanism in Eccentric Twin⁃screws Extruders Based on Lagrangian Method[J]. China Plastics, 2020, 34(8): 57-62.

Figures/Tables 10

Fig.1. Eccentric twin?screws geometric and finite element models

Fig.2. Effect of mesh cells on velocity

Fig.3. Forward time FTLE with different integration time while e=4 mm，t=0 s

Fig.4. Forward time FTLE with different initial time while e= 4 mm

Fig.5. Forward time FTLE with different initial time while e= 2 mm

Fig.6. Forward time FTLE while e=0 mm

Fig.7. Backward time FTLE with different initial time while e=4 mm

Fig.8. Hyperbolic LCS from different eccentricity models

Fig.9. Mixing index from different eccentricity models

Fig.10. Instantaneous efficiency with different eccentricity

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