Bubble size distribution in aerated stirred tanks: Quantifying the effect of impeller-stator design

• Published in: Chemical engineering research & design 2020-08, Vol.160, p.356-369
• Main Authors: Mesa, Diego, Brito-Parada, Pablo R.
• Format: Article
• Language: English
• Subjects: Aerated stirred tank; Aeration tanks; Aerodynamics; Air flow; Bubble size; Bubbles; Chemical reactions; Coalescing; Design optimization; Effects; Flotation; Impeller design; Impellers; Optimization; Rotor; Rushton turbine; Size distribution; Stator; Stators; Turbulence
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2020.05.029

[Display omitted] •Impeller design and operation have an important effect on bubble size.•Changes to impeller design affect the impact of impeller speed on bubble size.•The stator reduces d32 by reducing the number of large bubbles in the tank.•There is a critical impeller speed at which d32 is minimised regardless of air flow. Bubble size is an important variable in aerated stirred tanks as it determines the surface area available for reactions. In the bubble break-up process, impellers play a key role. Despite this importance, research into the effect of impeller design on bubble size is scarce. In this work we study the effect of two impellers, with and without a stator, as well as the effect of airflow rate, impeller speed and surfactant concentration on bubble size. Results show that there is a critical impeller speed above which bubble size is not further decreased, regardless of the airflow. Operating at this critical speed results in the smallest bubble size possible without additional turbulence. The reduction in bubble size caused by a stator was quantified for the first time and, interestingly, it was found that the stator also reduced the critical coalescence concentration. The implications of these findings for the design, evaluation and optimisation of impellers are discussed.