Oscillation dynamics of free vortex surface in uncovered unbaffled stirred vessels

Abstract The main feature of unbaffled stirred tanks is the highly swirling liquid motion, which leads to the formation of a central vortex on the liquid free surface, when the vessel is operated without top-cover (Uncovered Unbaffled Stirred Tanks, UUST). One of the main drawbacks of such vessels, that limits their industrial applicability, is the possible onset of low-frequency sloshing of the free surface. In this work, original data on oscillation dynamics in UUST are presented. In particular, data focus on the oscillation amplitude as well as on their frequency. Data were obtained by means of a novel experimental technique based on digital image analysis. The effect of impeller geometry (Rushton turbine, pitched blade turbine, Lightnin A310 propeller) and that of scale-up were finally investigated. It was found that the natural oscillation frequencies only depend on vessel scale and geometry, while impeller type plays a role in the way the free surface oscillation frequencies change with impeller speed.

[1]  K. C. Lee,et al.  Numerical simulations of the dependency of flow pattern on impeller clearance in stirred vessels , 2001 .

[2]  Alberto Brucato,et al.  Turbulent flow in closed and free-surface unbaffled tanks stirred by radial impellers , 1996 .

[3]  Alberto Brucato,et al.  Mixing dynamics in uncovered unbaffled stirred tanks , 2014 .

[4]  S. Nagata.  Mixing: Principles and Applications , 1975 .

[5]  Alberto Brucato,et al.  Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas–liquid operations , 2007 .

[6]  Alberto Brucato,et al.  Power consumption in uncovered-unbaffled stirred tanks: influence of viscosity and flow regime , 2013 .

[7]  M Yianneskis,et al.  Mixing time and kinetic energy measurements in a shaken cylindrical bioreactor , 2013 .

[8]  John W. Miles.  ON THE SLOSHING OF LIQUID IN A CYLINDRICAL TANK , 1956 .

[9]  Alberto Brucato,et al.  Solid−Liquid Suspensions in Top-Covered Unbaffled Vessels: Influence of Particle Size, Liquid Viscosity, Impeller Size, and Clearance , 2014 .

[10]  H. F. Bauer,et al.  Natural frequencies and response of spinning liquid column with apparently sliding contact line , 1993 .

[11]  Andrea Ducci,et al.  Orbitally shaken bioreactors—viscosity effects on flow characteristics , 2014 .

[12]  Alberto Brucato,et al.  Gas-liquid-solid Operation of a High Aspect Ratio Self-ingesting Reactor , 2012 .

[13]  Suzanne M. Kresta,et al.  Low frequency macroinstabilities in a stirred tank: scale-up and prediction based on large eddy simulations , 2003 .

[14]  Joannis Markopoulos,et al.  Vortex depth in unbaffled single and multiple impeller agitated vessels , 1995 .

[15]  Alberto Brucato,et al.  Free surface oxygen transfer in large aspect ratio unbaffled bio-reactors, with or without draft-tube , 2015 .

[16]  Piero M. Armenante,et al.  Flow regimes and surface air entrainment in partially filled stirred vessels for different fill ratios , 2012 .

[17]  Barbara Freudig,et al.  Dispersion of powders in liquids in a stirred vessel , 1999 .

[18]  K. C. Lee,et al.  On the origin, frequency and magnitude of macro-instabilities of the flows in stirred vessels , 2003 .

[19]  M Yianneskis,et al.  On the fluid dynamics of shaken bioreactors— flow characterization and transition , 2013 .

[20]  Alberto Brucato,et al.  Mass transfer and hydrodynamic characteristics of unbaffled stirred bio-reactors: Influence of impeller design , 2014 .

[21]  Valery N. Pilipchuk,et al.  Recent Advances in Liquid Sloshing Dynamics , 2001 .

[22]  Manabu Iguchi,et al.  Numerical Simulation on a Horizontal Flow Pattern of Jet-induced Rotary Sloshing in a Cylindrical Container , 2007 .

[23]  Manabu Iguchi,et al.  Prediction of the Occurrence of Swirl Motion at Interface between Stratified Two Liquids , 2005 .

[24]  Chris D. Rielly,et al.  Gas–Liquid–Solid Operation of a Vortex-Ingesting Stirred Tank Reactor , 2002 .

[25]  Antonio Busciglio,et al.  Free-surface shape in unbaffled stirred vessels: Experimental study via digital image analysis , 2013 .