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CFD simulation of local and global mixing time in an agitated tank

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Abstract

The Issue of mixing efficiency in agitated tanks has drawn serious concern in many industrial processes. The turbulence model is very critical to predicting mixing process in agitated tanks. On the basis of computational fluid dynamics(CFD) software package Fluent 6.2, the mixing characteristics in a tank agitated by dual six-blade-Rushton-turbines(6-DT) are predicted using the detached eddy simulation(DES) method. A sliding mesh(SM) approach is adopted to solve the rotation of the impeller. The simulated flow patterns and liquid velocities in the agitated tank are verified by experimental data in the literature. The simulation results indicate that the DES method can obtain more flow details than Reynolds-averaged Navier-Stokes(RANS) model. Local and global mixing time in the agitated tank is predicted by solving a tracer concentration scalar transport equation. The simulated results show that feeding points have great influence on mixing process and mixing time. Mixing efficiency is the highest for the feeding point at location of midway of the two impellers. Two methods are used to determine global mixing time and get close result. Dimensionless global mixing time remains unchanged with increasing of impeller speed. Parallel, merging and diverging flow pattern form in the agitated tank, respectively, by changing the impeller spacing and clearance of lower impeller from the bottom of the tank. The global mixing time is the shortest for the merging flow, followed by diverging flow, and the longest for parallel flow. The research presents helpful references for design, optimization and scale-up of agitated tanks with multi-impeller.

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Authors and Affiliations

  1. Key Laboratory of Testing Technology for Manufacturing Process of Ministry of Education, Southwest University of Science and Technology, Mianyang, 621010, China

    Liangchao Li & Bin Xu

Authors
  1. Liangchao Li
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  2. Bin Xu
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Corresponding author

Correspondence to Liangchao Li.

Additional information

Supported by Key Scientific Research Project of Sichuan Provincial Education Department (Grant No. 15ZA0107), and Doctor Foundation of Southwest University of Science and Technology(Grant No. 11zx7162)

LI Liangchao, born in 1976, is currently a teacher at Southwest University of Science and Technolgy, China. He received his PhD degree from Zhejiang University, China, in 2010. His research interests include fluid mixing technology, mechachonics engineering, fluid power transmission and control.

XU Bin, born in 1975, is currently an associate professor at Southwest University of Science and Technology. He received his PhD degree from Dalian University of Technology, China, in 2010. His research interests include mechachonics engineering, Rheology, fluid mixing technology.

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Li, L., Xu, B. CFD simulation of local and global mixing time in an agitated tank. Chin. J. Mech. Eng. 30, 118–126 (2017). https://doi.org/10.3901/CJME.2016.1107.129

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  • DOI: https://doi.org/10.3901/CJME.2016.1107.129

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