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The Movement and Mixing Effect of Polymer Fluid in the Embedded Planetary-screws Extruder

Author: WangXiaoLong
Tutor: XuBaiPingï¼›LiuYueJun
School: Hunan University
Course: Materials Science
Keywords: polymer processing numerical simulation chaotic mixing embedded planetary-screws
CLC: TQ320.52
Type: Master's thesis
Year: 2011
Downloads: 40
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Abstract


The single-screw extruder was widely used in many fields for its merits, such as sample structure, low cost and so on. More and more researchers pay attention to the design of the screw because of the poor mixing performance of the single-screw extruder. Reviewing the research progress of chaotic mixing in Hydromechanics, it can be found that the chaotic advection is better than the shear force in enhancing the mixing of non-Newtonian fluid. Some researches about chaotic mixing in polymer processing were published abroad, but this study in home is still very few. Consequently, study on the chaotic mixing in polymer processing is no doubt of great significance in science and reality.The numerical simulations of three-dimensional isothermal flow in the different embedded planetary-screws and the single-screw are carried out using finite-volume approach. The distributions of the velocity, pressure were obtained with the result that the shear-rate, the dispersion coefficient and the Residence Time Distribution(RTD) are investigated for single-screw and embedded planetary-screws. Compared with the traditional single-screw, the embedded planetary-screws leads to perturbation on the flow field and the material elements were suffered higher strain rate and elongation effect. The number and the diameter of the embedded planetary-screws and the depth of the channel of the center screw can have a profound effect on mixing effects of the material. The performance of the chaotic mixing in the planetary-screws is carried out by the particle track method, and the results revealed that the simplex way to show the mixing intensity cannot describe the mixing affect accurately without the consideration of the flow movement.The embedded six-planetary-screws extruder was developed successfully based on the embedded four-planetary-screws and the results of the simulation. A materiel composed of CaCO3&LLDPE is made by both the embedded six-planetary-screws and the co-rotating screws and analyzed by the SEM. The mixing affect of the planetary-screw which has a smaller aspect ratio can?achieve in the co-rotating screw of a bigger aspect ratio.By the use of CFD technology, some feasible geometry can be provided for the design of new screw, and it also can improve the efficiency of the design. It can be found that the planetary-screws both have the stabile extrusion characteristics of the single-screw and the strong shear rate of the co-rotating screws. This study has discussed the preliminary conception of chaotic mixing and provides a new way of the polymer processing development.

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CLC: > Industrial Technology > Chemical Industry > Synthetic resins and plastics industry > General issues > Machinery and equipment > Products processing molding equipment
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