Vortex Shape and Gas-Liquid Hydrodynamics in Unbaffled Stirred Tank

Abstract

Unbaffled stirred tanks are used in applications where the formation of a central vortex is desirable, such as in crystal growth, certain chemical reactions, and microalgae cultivation. The interaction between vortex ingestion and gas dispersion in these systems presents complex hydrodynamic behaviour that is not well characterised. This study investigated the effects of impeller speed and vortex ingestion on vortex shape, gas holdup, and bubble size distribution in an unbaffled stirred tank using optical probe measurements and volume of fluid (VOF) modelling.

The results show that without vortex ingestion, increased impeller speed causes significant vortex shape variation, while vortex shape remains relatively unchanged when ingestion occurs, suggesting that energy is directed toward gas dispersion rather than interface deformation. A large number of gas bubbles were entrained into the vortex core around the impeller region, resulting in lower gas holdup at upper axial locations. Higher impeller speeds produce larger bubbles due to the absence of baffles, which limits shear forces available for bubble break-up. These findings provide fundamental insight into the interplay between vortex dynamics and gas dispersion in unbaffled stirred tanks.

@article{prakash2019vortex,
  title         = {Vortex Shape and Gas-Liquid Hydrodynamics in Unbaffled Stirred Tank},
  author        = {Prakash, Baranivignesh and Bhatelia, Tejas and Wadnerkar, Divyamaan and Shah,
                  Milinkumar T and Pareek, Vishnu K and Utikar, Ranjeet P},
  year          = 2019,
  journal       = {The Canadian Journal of Chemical Engineering},
  volume        = 97,
  number        = 6,
  pages         = {1913--1920},
  doi           = {10.1002/cjce.23433}
}