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Language: English

Conflict of Interest: In relation to this article, we declare that there is no conflict of interest.

Publication history: Received December 11, 2007
Accepted March 7, 2008

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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A CFD model for predicting the flow patterns of viscous fluids in a bioreactor under various operating conditions

Byung-Hwan Um^† Thomas R. Hanley¹

Forest Bioproducts Research Initiative, Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469, USA ¹Department of Chemical Engineering, Samuel Ginn College of Engineering, Auburn University, Auburn, Alabama 36849, USA

BHUm@umche.maine.edu

Korean Journal of Chemical Engineering, September 2008, 25(5), 1094-1102(9), 10.1007/s11814-008-0179-y

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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_x000D_ Fluent (V. 6.2.20) and its preprocessor Mixsim (V. 2.1.10). The objective of this study is to ompare 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.

Keywords

Computational Fluid Dynamics (CFD) non-Newtonian Fluid Saccharification Followed by Fermentation (SFF),_x000D_ Multiple Reference Frame (MRF) Model High Solid Fermentation Rushton Turbine k-ε Turbulence Model

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