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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2021, Vol. 55 Issue (11): 2067-2075    DOI: 10.3785/j.issn.1008-973X.2021.11.006
    
Effect of screw structure on granular mixing in a double-screw conical mixer
Rui-huan CAI(),Yong-zhi ZHAO*()
Institute of Process Equipment, College of Energy Engineering, Zhejiang University, Hangzhou 310027, China
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Abstract  

The effects of different types of screws on granular mixing in a double-screw conical mixer were investigated by discrete element method (DEM). Specifically, the effects of the pitch diameter ratio (the ratio of the pitch to the diameter of the screw) and the screw diameter ratio (the ratio of the short screw diameter to the long screw diameter) on the mixing efficiency, device power and wear rate of the device were studied. Results show that different types of screws will affect the granular mixing, the device power as well as the device wear, however, the particles all can be well mixed after 100 s in the double-screw conical mixer with different screws. When other parameters remain unchanged, with the screw diameter ratio increasing, the mixing efficiency keeps similar, and the device power increases, but the wear rate of the device decreases. With the screw diameter ratio increasing, the mixing efficiency increases, and the device power increases, but the wear rate of the device fluctuates within a certain range.

Key words： discrete element method (DEM)      double-screw conical mixer      granular mixing      screw structure      device wear     
Received: 10 November 2020      Published: 05 November 2021
CLC:  TK 6  
Fund:  国家自然科学基金资助项目（22078283）；浙江大学博士研究生学术新星培养计划资助项目（2019030）
Corresponding Authors: Yong-zhi ZHAO     E-mail: rhcai@zju.edu.cn;yzzhao@zju.edu.cn
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Cite this article:

Rui-huan CAI,Yong-zhi ZHAO. Effect of screw structure on granular mixing in a double-screw conical mixer. Journal of ZheJiang University (Engineering Science), 2021, 55(11): 2067-2075.

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https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2021.11.006     OR     https://www.zjujournals.com/eng/Y2021/V55/I11/2067


双螺旋锥形混合器叶片结构对颗粒混合的影响

采用离散单元法（DEM），通过数值模拟研究双螺旋锥形混合器的叶片结构对颗粒混合的影响. 研究主要考察螺径比（双螺旋叶片的螺距和螺旋直径的比例）以及螺旋直径比（较短螺杆和较长螺杆的螺旋叶片直径的比例）对混合器混合效率、设备功率、设备磨损等的影响. 结果表明，不同双螺旋锥形混合器的叶片结构对颗粒的混合、设备功率、设备磨损产生影响，但是总体而言，在不同叶片结构的混合器中，颗粒经过100 s的混合之后都能够达到完全混合状态. 当保持其他参数不变时，随着螺径比的增大，混合器混合效率基本一致，设备功率增大，而设备磨损减小；随着螺旋直径比的增大，混合器混合效率有所提升，设备功率增大，而设备磨损并没有显著的改变.


关键词： 离散单元法(DEM),  双螺旋锥形混合器,  颗粒混合,  叶片结构,  设备磨损 
Fig.1 Double-screw conical mixer
类别 参数 数值
混合器参数 材料 钢
设备的维氏硬度 HV 370
顶部半径 R1/mm 400
底部半径 R2/mm 62.5
高度 H/mm 1 000
初始填充高度/mm 720
自转速度 Ω1/（r·min?1） 66.85
公转速度 Ω2/（r·min?1） 1.43
螺距 P1/mm 90、120、150、180、210
螺距 P2/mm 112.5、150.0、187.5、225.0、262.5
螺旋直径 D1/mm 120
螺旋直径 D2/mm 90、120、150、180、210
颗粒参数 颗粒直径 d/mm 13.5
颗粒密度/（kg·m?3） 2 600
颗粒数量 40 740
碰撞参数 摩擦系数 0.3
弹性恢复系数 0.9
法向弹性系数 kn/（N·m?1） 2.9 × 104
切向弹性系数 kt/（N·m?1） 1.2 × 104
时间步长/s 1 × 10?4
Tab.1 Parameters used in simulations for double-screw conical mixer
算例编号 P1/mm P2/mm D1/mm D2/mm P1/D1=P2/D2 D2/D1
1 90 112.5 120 150 0.75 1.25
2 120 150.0 120 150 1.00 1.25
3 150 187.5 120 150 1.25 1.25
4 180 225.0 120 150 1.50 1.25
5 210 262.5 120 150 1.75 1.25
6 150 187.5 120 90 1.25 0.75
7 150 187.5 120 120 1.25 1.00
8 150 187.5 120 180 1.25 1.50
9 150 187.5 120 210 1.25 1.75
Tab.2 Simulation cases for double-screw conical mixer
Fig.2 Comparison of geometries of different screws
Fig.3 Simulated snapshots of front view of granular mixing condition for case 3
Fig.4 Simulated axial snapshots of granular mixing condition for cases 1，3 and 5
Fig.5 Simulated axial snapshots of granular mixing condition for cases 6，3 and 9
Fig.6 Mixing index versus time for different cases
Fig.7 Device power for different cases
Fig.8 Wear rate for different cases
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