Statistical research on the mixing properties of wave based screws by numerical simulations

Tian-lei Liu; Yao-xue Du; Xian-yun He

doi:10.1515/ipp-2022-4253

Article

Statistical research on the mixing properties of wave based screws by numerical simulations

Tian-lei Liu , Yao-xue Du and Xian-yun He

Published/Copyright: February 15, 2023

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From the journal International Polymer Processing Volume 38 Issue 2

Abstract

Research based on numerical simulation with the CFD software ANSYS POLYFLOW is conducted on the mixing properties for the wave screw elements, as well as barrier screw elements, by using statistical tools. Then, the investigation is conducted in detail on the relationship between pressure, maximum shear rate, mixing index and other flow field characteristics of the two above screws under the same simulation conditions. It is found that polymer melt flow in the wave screw possesses various advantages compared with the normal barrier screw, such as acquiring larger pressure, stronger shearing and stretching action, better mixing and efficiency, which mainly result from the periodic depth change design in the screw groove. On the other hand, the increased wave bulge in the wave screw lessens the space for the polymer melt to be conveyed forward, which can greatly reduce the original function of the secondary flight. Also, the convergent and divergent zones in the wave screw groove produce a much stronger stress favoring the shear and elongation rates, and also lead to a sharp increase of the axial force load on the wave screw. Consequently, for the optimization of the wave screw configuration it is suggested to reduce the axial force without decreasing the effect of the excellent distributive and dispersive mixing.

Keywords: mixing efficiency; shear stress; wave configuration; wave screw

Corresponding author: Tian-lei Liu, Department of Mechanical Engineering, Guangdong Polytechnic of Industry and Commerce, Guangzhou 510510, Guangdong, China, E-mail: liusya0618@163.com

Funding source: National Natural Science Foundation of China

Award Identifier / Grant number: 11972023

Funding source: Special Project of College-enterprise Cooperation of Guangdong Polytechnic of Industry and Commerce

Award Identifier / Grant number: 2021-CJXY-06

Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: The authors wish to acknowledge the financial support of the National Natural Science Foundation of China (No: 11972023) and Special Project of College-enterprise Cooperation of Guangdong Polytechnic of Industry and Commerce (No: 2021-CJXY-06).
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.

Appendix A: Computation of the maximum shear rate

Using the min/max function from ANSYS POLYSTAT User’s Guide allows to calculate the minimum (or the maximum) of a property A along trajectories.

For example, in order to obtain the maximum shear rate, we select shear rate in the drop-down box near “The property A is … ” and tick the “0→t”, which means that the software counts the value of the shear rate till a given time t (0 < t < 4 s).

For example, let’s assume that there are 10 material particles, and that their shear rates corresponding to t = 0–4 s at an interval Δt = 0.4 s, respectively, are those shown in Table A1.

Table A1:

Shear rates of ten material particles at different time.

particles	1	2	3	4	5	6	7	8	9	10
t = 0.0 s	80	96	10	64	30	65	71	89	85	94
t = 0.4 s	93	64	41	86	28	28	87	60	48	35
t = 0.8 s	44	48	14	64	57	15	97	79	87	27
t = 1.2 s	23	61	39	25	57	62	73	49	14	76
t = 1.6 s	94	33	75	14	95	27	28	78	96	35
t = 2.0 s	46	19	88	52	54	14	87	69	24	48
t = 2.4 s	34	98	36	23	57	74	29	96	43	80
t = 2.8 s	43	78	23	34	88	25	15	64	25	31
t = 3.2 s	50	55	30	40	80	35	25	60	30	40
t = 3.6 s	96	50	33	72	70	40	41	55	35	44
t = 4.0 s	38	46	42	30	66	47	50	60	70	75

For a certain material particle, take the first particle as an example, its maximum of shear rates can be counted in the following way: The maximum shear rate for t (0→0 s) is 80; The maximum shear rate for t (0→0.4 s) is the bigger one between 80 (at t = 0 s) and 93 (at t = 0.4 s), that is 93; The maximum shear rate for t (0→0.8 s) is the biggest one among 80 (at t = 0 s), 93 (at t = 0.4 s) and 44 (at t = 0.8 s), that is 93; The maximum shear rate for t (0→1.2 s) is the biggest one among 80 (at t = 0 s), 93 (at t = 0.4 s), 44 (at t = 0.8 s)and 23 (at t = 0.8 s), that is 93; The maximum shear rate for t (0→1.6 s) is the biggest one among 80 (at t = 0 s), 93 (at t = 0.4 s), 44 (at t = 0.8 s), 23 (at t = 1.2 s) and 94 (at t = 1.6 s), that is 94.

The maximum shear rate for the ten particles at the moment t is obtained as explained below.

At t = 0.0 s, the maximum shear rate for Particle 1–10 is the shear rate 96 for Particle 2;
At t = 0.4 s, the maximum shear rate for Particle 1–10 is the shear rate 93 for Particle 1;
At t = 0.8 s, the maximum shear rate for Particle 1–10 is the shear rate 97 for Particle 7;
At t = 1.2 s, the maximum shear rate for Particle 1–10 is the shear rate 76 for Particle 10;
At t = 1.6 s, the maximum shear rate for Particle 1–10 is the shear rate 96 for Particle 9;
At t = 2.0 s, the maximum shear rate for Particle 1–10 is the shear rate 88 for Particle 3;
At t = 2.4 s, the maximum shear rate for Particle 1–10 is the shear rate 98 for Particle 2;
At t = 2.8 s, the maximum shear rate for Particle 1–10 is the shear rate 88 for Particle 5;
At t = 3.2 s, the maximum shear rate for Particle 1–10 is the shear rate 80 for Particle 5;
At t = 3.6 s, the maximum shear rate for Particle 1–10 is the shear rate 96 for Particle 1;
At t = 4.0 s, the maximum shear rate for Particle 1–10 is the shear rate 75 for Particle 10.

Then the maximum shear rate can be drawn for the ten particles as a function of time shown in Figure A-1.

Figure A-1:

Maximum shear rate as a function of time.

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Received: 2022-06-30

Accepted: 2022-12-26

Published Online: 2023-02-15

Published in Print: 2023-05-25

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Articles in the same Issue

https://doi.org/10.1515/ipp-2022-4253

Keywords for this article

mixing efficiency; shear stress; wave configuration; wave screw