CFD study on double-to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine

doi:10.1016/j.cjche.2018.10.002

中国化学工程学报 ›› 2019, Vol. 27 ›› Issue (5): 993-1000.DOI: 10.1016/j.cjche.2018.10.002

• Fluid Dynamics and Transport Phenomena • 上一篇下一篇

CFD study on double-to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine

Quanhong Zhu^1,2, Hang Xiao^1,2, Aqiang Chen^1,2, Shujun Geng^1,2, Qingshan Huang^1,2,3

1 Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China;
2 Dalian National Laboratory for Clean Energy, Dalian 116023, China;
3 Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China

收稿日期:2018-07-10 修回日期:2018-08-18 出版日期:2019-05-28 发布日期:2019-06-27
通讯作者: Qingshan Huang
基金资助:
Supported by the National Key Research and Development Program of China (2016YFB0301701), the National Natural Science Foundation of China (91434114; 21376254), the Instrument Developing Project of the CAS (YZ201641), “Transformational Technologies for Clean Energy and Demonstration”, Strategic Priority Research Program of the CAS (XDA21060400), and CAS Key Technology Talent Program.

CFD study on double-to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine

Quanhong Zhu^1,2, Hang Xiao^1,2, Aqiang Chen^1,2, Shujun Geng^1,2, Qingshan Huang^1,2,3

1 Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China;
2 Dalian National Laboratory for Clean Energy, Dalian 116023, China;
3 Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China

Received:2018-07-10 Revised:2018-08-18 Online:2019-05-28 Published:2019-06-27
Contact: Qingshan Huang
Supported by:
Supported by the National Key Research and Development Program of China (2016YFB0301701), the National Natural Science Foundation of China (91434114; 21376254), the Instrument Developing Project of the CAS (YZ201641), “Transformational Technologies for Clean Energy and Demonstration”, Strategic Priority Research Program of the CAS (XDA21060400), and CAS Key Technology Talent Program.

摘要/Abstract

摘要： For a fully baffled tank stirred by a Rushton turbine (RT), the flow pattern will change from double-to single-loop as the off bottom clearance (C) of the RT decreases from one third of the tank diameter. Such a flow pattern transition as well as its influence on the macro mixing efficiency was investigated via CFD simulation. The transient sliding mesh approach coupled with the standard k-ε turbulence model could correctly and efficiently reproduce the reported critical C range where the flow pattern changes. Simulation results indicated that such a critical C range varied hardly with the impeller rotation speed but decreased significantly with increasing impeller diameter. Small RTs are preferable to generating the single-loop flow pattern. A mechanism of the flow pattern transition was further proposed to explain these phenomena. The discharge stream from the RT deviates downwards from the horizontal direction for small C values; if it meets the tank wall first, the double-loop will form; if it hits the tank bottom first, the single-loop will form. With the flow pattern transition, the mixing time decreased by about 35% at the same power input (P), indicating that the single-loop flow pattern was more efficient than the double-loop to enhance the macro mixing in the tank. A comparison was further made between the single-loop RT and pitched blade turbine (PBT, 45°) from macro mixing perspective. The single-loop RT was found to be less efficient than the PBT and usually required 60% more time to achieve the same level of macro mixing at the same P.

关键词: Rushton turbine, Flow pattern, Transition, Simulation, Mechanism, Mixing

Abstract: For a fully baffled tank stirred by a Rushton turbine (RT), the flow pattern will change from double-to single-loop as the off bottom clearance (C) of the RT decreases from one third of the tank diameter. Such a flow pattern transition as well as its influence on the macro mixing efficiency was investigated via CFD simulation. The transient sliding mesh approach coupled with the standard k-ε turbulence model could correctly and efficiently reproduce the reported critical C range where the flow pattern changes. Simulation results indicated that such a critical C range varied hardly with the impeller rotation speed but decreased significantly with increasing impeller diameter. Small RTs are preferable to generating the single-loop flow pattern. A mechanism of the flow pattern transition was further proposed to explain these phenomena. The discharge stream from the RT deviates downwards from the horizontal direction for small C values; if it meets the tank wall first, the double-loop will form; if it hits the tank bottom first, the single-loop will form. With the flow pattern transition, the mixing time decreased by about 35% at the same power input (P), indicating that the single-loop flow pattern was more efficient than the double-loop to enhance the macro mixing in the tank. A comparison was further made between the single-loop RT and pitched blade turbine (PBT, 45°) from macro mixing perspective. The single-loop RT was found to be less efficient than the PBT and usually required 60% more time to achieve the same level of macro mixing at the same P.

Key words: Rushton turbine, Flow pattern, Transition, Simulation, Mechanism, Mixing

Quanhong Zhu, Hang Xiao, Aqiang Chen, Shujun Geng, Qingshan Huang. CFD study on double-to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine[J]. 中国化学工程学报, 2019, 27(5): 993-1000.

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CFD study on double-to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine

CFD study on double-to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine

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