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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

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Chinese Journal of Chemical Engineering 2019年第5期27卷 993-1000页

作者： Quanhong Zhu Hang Xiao Aqiang Chen Shujun Geng Qingshan Huang Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of SciencesQingdao 266101China Dalian National Laboratory for Clean Energy Dalian 116023China Key Laboratory of Green Process and Engineering Institute of Process EngineeringChinese Academy of SciencesBeijing 100190China

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.

关键词： rushton turbine Flow pattern Transition Simulation Mechanism Mixing

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CFD Prediction of the Turbulent Flow Generated in Stirred Square Tank by a rushton Turbine

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Energy and Power Engineering 2014年第5期6卷 95-110页

作者： W. Chtourou M. Ammar Z. Driss M. S. Abid National School of Engineers of Sfax (ENIS) Department of Mechanical Engineering Laboratory of Electromechanical Systems (LASEM) Sfax Tunisia

The Computational Fluid Dynamics (CFD) have been used in the analysis and design of agitated vessel. Most of the researches done in this area are limited to the baffled or unbaffled stirred tank. In this paper, we have been interested in studying of the new design. Particularly, the flow and turbulence fields in square vessel stirred by a standard rushton turbine have been simulated by means of CFD techniques. The Navier-Stokes equations governing the phenomenon of transfer of momentum are solved by a discretization method for finite volume. The MRF approaches can be used in simulation of the steady state problem. The numerical results from the application of CFD code Fluent with the stationary approach Multi Reference Frame (MRF) are presented in the planes containing the blade. The validation of CFD results with experimental measurements showed a good agreement.

关键词： CFD Mixing Turbulent rushton Turbine Stirred Vessel

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rushton搅拌釜中单相流场DES模拟与通气功率模型研究

Rushton搅拌釜中单相流场DES模拟与通气功率模型研究

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作者：罗云峰湘潭大学

学位级别：硕士

搅拌釜反应器由于其外加机械搅拌,液相湍动剧烈,具有混合效果好、相接触面积大、传热和传质效率高等特点而在化工、生物、食品、制药等工业过程中有着非常广泛的应用。然而,与其有关的理论及计算方法却仍不完善,许多还是处在半经验半理... 详细信息

搅拌釜反应器由于其外加机械搅拌,液相湍动剧烈,具有混合效果好、相接触面积大、传热和传质效率高等特点而在化工、生物、食品、制药等工业过程中有着非常广泛的应用。然而,与其有关的理论及计算方法却仍不完善,许多还是处在半经验半理论阶段。因而,越来越多的学者利用计算流体力学（Computational Fluid Dynamics,CFD）方法可以对搅拌过程进行数值模拟,使得流场可视化,给人们以清晰的认识。在湍流模拟方面,主要可分为直接数值模拟（DNS）、大涡模拟（LES）、雷诺平均方法（RANS）三种。脱体涡数值模拟（DES）是近年来出现的一种结合了雷诺平均方法（RANS）和大涡数值模拟（LES）两者优点的湍流模拟方法,可以被用来有效且快速的模拟大范围分离的湍流流动。据此,本文首次利用脱体涡数值分析方法（Detached eddy simulation, DES）研究了rushton涡轮桨搅拌釜内的流动特性,并将模拟结果与RANS、LES模型及文献实验数据进行了比较。结果表明:DES方法可获得搅拌釜内的瞬态流场;对桨叶区时均速度及湍流动能的预测与实验数据较吻合,比RANS模型计算结果有明显改进,所需的运算时间比LES模型要少。另外考虑到传统经验关联式在工程上的简单易用性,而rushton气液搅拌釜反应器通气时的搅拌功耗又是其设计与放大最重要的参数之一,国内外虽报道了不少关联式,但当通气速率很小时就会失去其合理性。所以本文对通气功率进行了探讨,首次提出将其分为两个部分考虑,建立了较为合理,且高精度的新型Weibull功率模型,具有一定的现实意义。

关键词：搅拌釜 rushton 计算流体力学脱体涡数值模拟 Weibull模型

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