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Characterization of the Gas Dispersion Behavior of Multiple Impeller Stages by Flow Regime Analysis and CFD Simulations
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  • Sören Bernauer,
  • Mathias Schöpf,
  • Philipp Eibl,
  • Christian Witz,
  • Johannes Khinast,
  • Timo Hardiman
Sören Bernauer
Sandoz GmbH
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Mathias Schöpf
Sandoz GmbH
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Philipp Eibl
Technische Universität Graz
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Christian Witz
Technische Universität Graz
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Johannes Khinast
Technische Universität Graz
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Timo Hardiman
Sandoz GmbH
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Abstract

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 plays a key role in a better gas retention efficiency of the upper impellers. In contrast, a flooded bottom impeller adversely affects the gas dispersion of all impellers. A novel analysis of the bubble flow in the dispersed state via a two-phase 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.

Peer review status:UNDER REVIEW

28 Jun 2020Submitted to Biotechnology and Bioengineering
29 Jun 2020Assigned to Editor
29 Jun 2020Submission Checks Completed
18 Jul 2020Reviewer(s) Assigned
29 Aug 2020Editorial Decision: Revise Major
29 Aug 2020Review(s) Completed, Editorial Evaluation Pending