Effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks--颗粒学报PARTICUOLOGY

Xu, W., Tan, Y., Li, M., Sun, J., Xie, D., & Liu, Z. (2020). Effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks. Particuology, 49, 159-168. https://doi.org/10.1016/j.partic.2019.03.005

Effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks

Wentao Xu ^a, Yangbo Tan ^b, Meng Li ^b, Jianglong Sun ^{b c d}, De Xie ^{b c d}, Zeng Liu ^{b c d *}

a School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
b School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
c Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China
d Hubei Key Laboratory of Naval Architecture and Ocean Engineering Hydrodynamics, Wuhan 430074, China

10.1016/j.partic.2019.03.005

Volume 49, April 2020,, Pages 159-168

Received 16 January 2018, Revised 2 July 2018, Accepted 18 March 2019, Available online 27 June 2019, Version of Record 26 February 2020.

E-mail: z_liu@hust.edu.cn

Highlights

• Particle dispersion was analyzed during stirring in baffled and unbaffled tanks.

• Critical impeller speed was defined by particle distribution behavior.

• A dispersion index reasonably predicted particle drawdown in unbaffled tank.

• Baffles suppressed the surface vortex and more uniformly distributed particles.

• Baffled tanks increased power consumption.

Abstract

The effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks were investigated. Particle distribution and power consumption were analyzed by experiments and numerical simulations in both baffled and unbaffled tanks agitated by a Rushton impeller. In unbaffled tanks, a non-aggregation rule was applied and the average dispersion index was found to serve as a reasonable prediction of the full drawdown of floating particles. The critical impeller speeds in an unbaffled tank were higher than those in a tank with vertical baffles. At each immersion depth in a baffled tank, particles distributed more uniformly and more power was consumed. Comparison of snapshots of the baffled and unbaffled tanks shows that the surface vortex increases the drawdown speed while it decreases the particle distribution uniformity and power consumption. Therefore, the use of baffles to suppress the surface vortex provides for a more uniform particle distribution in stirred tanks.

Graphical abstract

Keywords

Stirred tank; Surface vortex; Solids drawdown; Complete dispersion

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