A CFD model for predicting the flow patterns of viscous fluids in a bioreactor under various operating conditions |
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Authors: | Byung-Hwan Um Thomas R Hanley |
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Affiliation: | (1) Forest Bioproducts Research Initiative, Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469, USA;(2) Department of Chemical Engineering, Samuel Ginn College of Engineering, Auburn University, Auburn, Alabama 36849, USA |
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Abstract: | Computational fluid dynamics simulation is becoming an increasingly useful tool in the analysis and design of simultaneous
saccharification fermentation (SSF) and saccharification followed by fermentation process (SFF). To understand and improve
mixing and mass transfer in a highly viscous non-Newtonian system, it was necessary to simulate the flow behavior in this
bench scale bioreactor (BioFlo 3000). This study focused on designing a high concentration medium agitation system for such
a process using the commercial computational fluid dynamics package Fluent (V. 6.2.20) and its preprocessor Mixsim (V. 2.1.10).
The objective of this study is to compare performance of various designs of a bioreactor and identify the flow pattern and
related phenomena in the bench scale tank. The configuration of the physical model for simulating a mixing tank with a Rushton
impeller consists of an ellipsoidal cylindrical tank with four equally spaced wall mounted baffles extending the vessel bottom
to the free surface, stirred by a centrally located six-blade Rushton turbine impeller. Simulations were performed with the
original and a modified design in which the lower bottom shaft mounted a Lightnin A200 impeller. The results suggest that
there is a potential for slow or stagnant flow between top impellers and bottom of the tank region, which could result in
poor nitrogen and heat transfer for highly viscous fermentations. The results also show that the axial velocity was significantly
improved for the modified geometry in the bottom of the tank. |
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Keywords: | Computational Fluid Dynamics (CFD) non-Newtonian Fluid Saccharification Followed by Fermentation (SFF) Multiple Reference Frame (MRF) Model High Solid Fermentation Rushton Turbine k-ɛ Turbulence Model |
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