Unsteady Mixing Characteristics in a Vessel with Forward-Reverse Rotating Impeller

Usually, mixing is carried out in a vessel with four baffles and a single impeller. In some applications, however, the use of a baffled vessel is not recommended. One of the stirring methods used instead is unsteady agitation with forward-reverse rotating impellers. The aim of this work was to characterize the agitation characteristics in a baffled and an unbaffled vessel with a turbine impeller. Mixing time and mixing power were evaluated in relation to the presence of baffles and the frequency of forward-reverse rotation. It was found that the frequency of oscillation does not affect either the mixing time and mixing power values or the drag and added mass coefficients. Power requirements and mixing time were higher compared to the steady mixing conditions in a baffled vessel. The results showed that it is not recommended to use baffles because they have no influence on unsteady mixing.

[1]  Chiara Galletti,et al.  On the main flow features and instabilities in an unbaffled vessel agitated with an eccentrically located impeller , 2008 .

[2]  振動流中に置かれた種々な断面辺長比の矩形柱周りの流れ特性 ( 流体関連振動・騒音等) , 1999 .

[3]  J. Landau,et al.  Studies on mixing. XII. Homogenation of miscible liquids in the turbulent region , 1961 .

[4]  Shuichi Iwata,et al.  Improvement of Mixing Efficiencies of Conventional Impeller with Unsteady Speed in an Impeller Revolution , 2005 .

[5]  S. Dennis,et al.  Unsteady flow past a rotating circular cylinder at Reynolds numbers 103 and 104 , 1990, Journal of Fluid Mechanics.

[6]  Turgut Sarpkaya,et al.  Force on a circular cylinder in viscous oscillatory flow at low Keulegan—Carpenter numbers , 1986, Journal of Fluid Mechanics.

[8]  Octave Levenspiel,et al.  New scale-up and design method for stirrer agitated batch mixing vessels , 1976 .

[9]  Philippe A. Tanguy,et al.  Effect of shaft eccentricity on the laminar mixing performance of a radial impeller , 2008 .

[10]  M. Yoshida,et al.  Turbulent and Laminar Mixings in an Unbaffled Agitated Vessel with an Unsteadily Angularly Oscillating Impeller , 2009 .

[11]  Fernando J. Muzzio,et al.  Laminar mixing in eccentric stirred tank systems , 2008 .

[12]  G. Kopp,et al.  The suppression of periodic vortex shedding from a rotating circular cylinder , 2008 .

[13]  Kazuaki Yamagiwa,et al.  Liquid‐phase mixing in an unbaffled agitated vessel with an unsteady forward–reverse rotating impeller , 2007 .

[14]  H. Kramers,et al.  A comparative study on the rate of mixing in stirred tanks , 1953 .

[15]  J. Joshi,et al.  Liquid-phase mixing in stirred vessels: turbulent flow regime , 2003 .

[16]  C. Hoogendoorn,et al.  Model studies on mixers in the viscous flow region , 1967 .

[17]  Fernando J. Muzzio,et al.  Using time-dependent RPM to enhance mixing in stirred vessels , 1996 .

[18]  Xiongwei Ni,et al.  On the discussion of the dimensionless groups governing oscillatory flow in a baffled tube , 1997 .

[19]  Kazuaki Yamagiwa,et al.  Power characteristics of unsteadily forward–reverse rotating impellers in an unbaffled aerated agitated vessel , 2001 .

[20]  G. Montante,et al.  Effect of the shaft eccentricity on the hydrodynamics of unbaffled stirred tanks , 2006 .

[21]  Kit Ming Lam,et al.  Vortex shedding flow behind a slowly rotating circular cylinder , 2009 .

[22]  Magdalena Cudak,et al.  Stirring of a liquid in a stirred tank with an eccentrically located impeller , 2005 .

[23]  M. Yoshida,et al.  Liquid flow in impeller region of an unbaffled agitated vessel with an angularly oscillating impeller , 2008 .

[24]  Alvin W. Nienow,et al.  On impeller circulation and mixing effectiveness in the turbulent flow regime , 1997 .