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

作     者：Quanhong Zhu Hang Xiao Aqiang Chen Shujun Geng Qingshan Huang 

作者机构：Key Laboratory of BiofuelsQingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of SciencesQingdao 266101China Dalian National Laboratory for Clean EnergyDalian 116023China Key Laboratory of Green Process and EngineeringInstitute of Process EngineeringChinese Academy of SciencesBeijing 100190China 

出 版 物：《Chinese Journal of Chemical Engineering》 (中国化学工程学报（英文版）)

年 卷 期：2019年第27卷第5期

页      面：993-1000页

核心收录：

学科分类：0817[工学-化学工程与技术] 08[工学] 

基　　金：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) CAS Key Technology Talent Program 

主　　题：Rushton turbine Flow pattern Transition Simulation Mechanism Mixing 

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-s 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 phe no mena. The discharge stream from the RT deviates down wards 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.