Characterization of the Gas Dispersion Behavior of Multiple Impeller Stages by Flow Regime Analysis and CFD Simulations

Sören Bernauer*, Mathias Schöpf, Philipp Eibl, Christian Witz, Johannes Khinast, Timo Hardiman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Multiple impeller reactors are widely used due to their advanced gas utilization and an increased volumetric mass transfer coefficient. However, with the application of Rushton impellers, gas dispersion efficiency varies between the bottom and the upper impeller levels. The present study analyzes the individual flow regime, power input and gas hold‐up in each compartment of a reactor equipped with four Rushton impellers. The results indicate that the pre‐dispersion of the air introduced by the bottom impeller (up to 80 %) plays a key role in a better gas retention efficiency of the upper impellers (> 300 %) and leads to a shift of the cavity and flooding lines in the flow map (Fr‐ vs Fl‐Number) of the upper impellers. A novel analysis of the bubble flow in the dispersed state via a two‐phase LES‐based CFD model reveals that a more homogenous distribution of air bubbles in the upper compartments leads to high compartment gas hold‐up values, but fewer bubbles in the vicinity of the impellers. The measured and simulated data of this study indicate that the upper impellers' efficiency mostly depends on the flow regime of and the pre‐dispersion by the bottom impeller rather than on the upper impellers' flow regimes. These results contribute to the understanding of essential mixing processes and scaling of aerated bioreactors
Original languageEnglish
Pages (from-to)3058-3068
Number of pages11
JournalBiotechnology and Bioengineering
Issue number8
Publication statusPublished - Aug 2021


  • bubble dispersion
  • CFD
  • flooding
  • flow regime analysis
  • multiple impeller reactor

ASJC Scopus subject areas

  • Biotechnology
  • Bioengineering
  • Applied Microbiology and Biotechnology

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