| 1. |
- Enfors, Sven-Olof, et al.
(författare)
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Physiological responses to mixing in large scale bioreactors
- 2001
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Ingår i: Journal of Biotechnology. - 0168-1656 .- 1873-4863. ; 85:2, s. 175-185
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Tidskriftsartikel (refereegranskat)abstract
- Escherichia coli fed-batch cultivations at 22 m(3) scale were compared to corresponding laboratory scale processes and cultivations using a scale-down reactor furnished with a high-glucose concentration zone to mimic the conditions in a feed zone of the large bioreactor. Formate accumulated in the large reactor, indicating the existence of oxygen limitation zones. It is suggested that the reduced biomass yield at large scale partly is due to repeated production/reassimilation of acetate from overflow metabolism and mixed acid fermentation products due to local moving zones with oxygen limitation. The conditions that generated mixed-acid fermentation in the scale-down reactor also induced a number of stress responses, monitored by analysis of mRNA of selected stress induced genes. The stress responses were relaxed when the cells returned to the substrate limited and oxygen sufficient compartment of the reactor. Corresponding analysis in the large reactor showed that the concentration of mRNA of four stress induced genes was lowest at the sampling port most distant from the feed zone. It is assumed that repeated induction/relaxation of stress responses in a large bioreactor may contribute to altered physiological properties of the cells grown in large-scale bioreactor. Flow cytometric analysis revealed reduced damage with respect to cytoplasmic membrane potential and integrity in cells grown in the dynamic environments of the large scale reactor and the scale-down reactor.
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| 2. |
- Kovacs, T., et al.
(författare)
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Flow and turbulence in the discharge of radial pumping turbines : Influence of the turbine type
- 2001
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Ingår i: Chemical Engineering & Technology. - 0930-7516 .- 1521-4125. ; 24:10, s. 1035-1044
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Tidskriftsartikel (refereegranskat)abstract
- Velocity measurements were made in the impeller discharge of 6SRGT- and Rushton-type impellers in a 0.6 m(3) tank using, constant temperature anemometry with a direction sensitive split-film probe. The reproducibility error of the measurement system was found to be greater than 5 % for all measured properties. The main flow and turbulent parameters measured at three agitation rates in the impeller discharge are compared for the two turbines with respect to both agitation rate and the measured power input. For comparison of the flow properties in the centerline of the two turbines having different diameter and blade height, a uniform representation was used treating the impeller stream as a special kind of free jet. Using this representation, we obtained similar results for both turbines on all measured parameters. The profile measurements showed a similar main flow field for both turbines, but significant differences were found in the axial distribution of turbulent kinetic energy and the energy dissipation rate.
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| 3. |
- Kovacs, T., et al.
(författare)
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Fourier spectrum to recover deterministic and stochastic behavior in stirred tanks
- 2001
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 47:10, s. 2167-2176
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Tidskriftsartikel (refereegranskat)abstract
- Velocity data from the impeller region of Rushton and 6SRGT pilot-scale impellers were analyzed both in the frequency domain and with respect to periodicity. The four characteristic frequencies and their combination were detected from the Fourier spectrum, and the deterministic part of the signal was recovered by making the amplitude of the other frequencies zero. The deterministic part was then analyzed with tools from nonlinear theories. For the two turbine-types, the dynamics of the deterministic velocity parts were almost identical. The turbulent part of the signal could also be estimated in a similar manner.
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| 4. |
- Revstedt, Johan, et al.
(författare)
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Influence of impeller type on the flow and mixing in a stirred reactor
- 2000
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Ingår i: AIChE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 46:12, s. 2373-2382
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations (LES) of a stirred reactor with a liquid volume of 0.64 m3 were performed. The tank was stirred by either two standard Rushton impellers or two Scaba 6SRGT impellers. The LES can provide details of the flow field that cannot be obtained with so‐called Reynolds‐averaged equations and the corresponding models. The unsteady spatially filtered incompressible Navier‐Stokes equations were solved together with a transport equation for the concentration of an inert additive using a multigrid finite difference code with a staggered grid. The unresolved turbulent scales were modeled using a scale similarity model. The aim of this investigation has been to study the influence of impeller type on the flow structure and scalar transport. The results show that, compared at equal power input, the center plane velocities and the volume flow in the impeller stream do not differ much for the impeller types. Also, for the 6SRGT the periodic fluctuations associated with the blade passing is less pronounced
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| 5. |
- Revstedt, J., et al.
(författare)
-
Influence of impeller type on the flow structure in a stirred reactor
- 2000
-
Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 46:12, s. 2373-2382
-
Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations (LES) of a stirred reactor with a liquid volume of 0.64 m(3) were performed. The tank was stirred by either two standard Rushton impellers or two Scaba 6SRGT impellers. The LES can provide details of the flow field that cannot be obtained with so-called Reynolds-averaged equations and the corresponding models. The unsteady spatially filtered incompressible Navier-Stokes equations were solved together with a transport equation for the concentration of an inert additive using a multigrid finite difference code with a staggered grid. The unresolved turbulent scales were modeled using a scale similarity model. The aim of this investigation has been to study the influence of impeller type on the flow structure and scalar transport. The results show that, compared at equal power input, the center plane velocities and the volume flow in the impeller stream do not differ much for the impeller types. Also, for the 6SRGT the periodic fluctuations associated with the blade passing is less pronounced.
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