Investigation on flow field in stirred tank equipped with three-blade swept-back-HEDT combined impeller by experiment and simulation

doi:10.11949/0438-1157.20190800

Abstract

Abstract:

The flow field in a stirred tank with three-blade swept-back HEDT combined impeller for polyethylene polymerization was simulated. The effects of the installation height of impellers (C ₁), the distance between two impellers (C ₂) and the rotational speed of the combined impeller(N) on the flow field in the stirred tank were analyzed, and the simulation results were validated by PIV experiments. The comparison between the three-blade swept-back HEDT and the three-blade swept-six straight blade disc turbine combined propeller are carried out. The results show that when the ratio of propeller spacing to vessel diameter is 0.35, the fluid flow between the blades in the stirred tank is the best, and the velocity distribution of the upper fluid in the stirred tank is improved. When the installation height of impellers to vessel diameter is 0.29, an overall circulation occurs under the combined paddle, which is beneficial to the mixing of the bottom fluid of the kettle. When N = 90 r/min, the fluid velocity distribution in the kettle is uniform, and the jet direction produced by the upper HEDT blade tends to be horizontal. The comparison between the combined impeller and the three-blade swept-six-straight blade disc turbine shows that the flow pattern of the two combined impellers is similar, but the mixing power of the former can be significantly reduced. The research results can provide reference for engineering application of three-blade sweep-HEDT combined impeller in the polyethylene polymerization reactor.

Key words: three-blade swept-back-HEDT combined impeller, stirred vessel, PIV, CFD

摘要：

对应用于聚乙烯聚合反应中的三叶后掠-HEDT组合桨的搅拌釜内流场进行了模拟研究，分析组合桨的离底距C ₁、桨间距C ₂以及转速N的变化对搅拌釜内流场的影响，利用PIV实验对模拟结果进行了验证；将该组合桨与三叶后掠-六直叶圆盘涡轮组合桨进行了模拟对比研究。结果表明：当桨间距与釜内径的比为0.35时，釜内桨叶间的流体流动效果最好，该条件下能够改善搅拌釜上层流体的速度分布；当离底距与釜内径的比值为0.29时，组合桨下方出现了整体的环流，有利于釜底流体的混合；桨叶转速N=90 r/min时釜内流体速度分布均匀，同时上层HEDT桨叶产生的射流方向趋于水平。两种组合桨的对比研究表明：二者流型相近，但前者搅拌功率能够得到明显降低。研究结果可为三叶后掠-HEDT组合桨在聚乙烯聚合反应釜中的工程应用提供参考。

关键词: 三叶后掠-HEDT组合桨, 搅拌容器, PIV, CFD

CLC Number:

TQ 022

Yongjun ZHOU, Mingyue YUAN, Haopeng XU, Hua HE, Jianping SUN. Investigation on flow field in stirred tank equipped with three-blade swept-back-HEDT combined impeller by experiment and simulation[J]. CIESC Journal, 2019, 70(12): 4599-4607.

周勇军, 袁名岳, 徐昊鹏, 何华, 孙建平. 三叶后掠-HEDT组合桨搅拌釜内流场的模拟及实验[J]. 化工学报, 2019, 70(12): 4599-4607.

Figures/Tables 15

Fig.1 Size and structure of three-blade swept-back combined impeller

Table1 Main operating parameters of stirred tank and impellers

参数	尺寸/mm
h	675
H	700
T	430
D ₁	184
D ₂	184
C ₁	100
C ₂	100

Fig.2 Grid of computational region

Table 2 Effect of grid size on power number and deviation

网格数量/万	扭矩	相对偏差/%
83	0.0591	—
92	0.0550	7.45
103	0.0523	5.16
116	0.0508	2.95
127	0.0500	1.56

Table 3 Geometry and operating parameters of stirred tank

工况	N/(r/min)	C ₁/mm	C ₂/mm
1	60	75	200
2	60	125	200
3	60	175	200
4	60	125	100
5	60	125	150
6	60	125	200
7	60	125	150
8	90	125	150
9	120	125	150

Fig.3 Simulated velocity cloud chart of combined impellers at different installation height of impellers

Fig.4 Simulated streamline diagrams of combined impellers at different installation height of impellers

Fig.5 Simulated velocity cloud chart of combined impellers with different paddle pitches

Fig.6 Simulated streamline diagrams of combined impellers at distance between two impellers

Fig.7 Simulated streamline diagrams of combined impellers at different rotational speed

Table 4 Power consumption of two combined impellers under different speed

转速/(r/min)	三叶后掠-HEDT/W	三叶后掠-六直叶圆盘涡轮桨/W	搅拌功率减少率/%
60	0.5	0.64	21.8
90	1.58	2.14	26.2
120	3.63	4.86	25.3
150	6.93	9.17	24.4

Fig.8 Simulated streamline diagrams of two combined impellers

Fig.9 Flow field test platform of stirred tank

Fig.10 Flow field comparison of experiment and simulation

Fig.11 Contrast of radial and axial velocities

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