Transition from turbulent to transitional flow in the top half of a stirred tank

Machado, Márcio B.; Bittorf, Kevin J.; Roussinova, Vesselina; Kresta, Suzanne M.

doi:10.1016/j.ces.2013.04.039

Cited by 36 publications

(25 citation statements)

References 84 publications

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“…Figure shows the average cloud height at different impeller speeds and particle loadings. Interestingly, Kresta and coworkers observed a similar linear dependency on Reynolds number, when investigating the vertical extent of fully developed turbulence in a single phase mixer.…”

Section: Resultsmentioning

confidence: 66%

Analysis of particle cloud height dynamics in a stirred tank

2015

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Local and temporal variations of the particle cloud formed in a cylindrical mixing vessel were investigated experimentally. Different particle sizes (0.5, 1, and 2 mm) and volumetric concentration up to 20 vol % were evaluated at different impeller speeds. The time-averaged cloud height was linear with impeller frequency and with volume concentration. Suspensions with larger particles had a lower average cloud height, while the standard deviation for the temporal cloud height variation was larger. Two strong periodic phenomena were identified to be dominating the particle cloud height variations. The frequencies were linear with impeller speed, resulting in dimensionless frequencies of S 1 50.02-0.03 and S 2 50.05-0.06. The frequencies were affected by neither the particle size nor the volumetric concentration. The amplitude showed no dependency on the particle size, but the S 2 amplitude significantly decreases and S 1 increases with increasing solid concentration. The results were compared to LES/discrete element method simulations and showed a fair agreement.

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Section: Resultsmentioning

confidence: 66%

Analysis of particle cloud height dynamics in a stirred tank

2015

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“…This seems to be consistent with the results obtained by Zhang et al, 29 who found Reynolds independent flow behaviour for Re > 6,000 in a small sized stirred tank vessel ( T = 28.5 cm) equipped with a Rushton Turbine impeller. Similarly, Machado et al 30,31 also showed low Re associated to turbulent flow regimes for both axial and radial flow impeller types. Generally, lower ranges in Re have been associated with the turbulent flow transition as the impeller to tank diameter ( D / T ) ratio increases and with decreasing vessel size 29‐32 .…”

Section: Resultsmentioning

confidence: 79%

“…Similarly, Machado et al 30,31 also showed low Re associated to turbulent flow regimes for both axial and radial flow impeller types. Generally, lower ranges in Re have been associated with the turbulent flow transition as the impeller to tank diameter ( D / T ) ratio increases and with decreasing vessel size 29‐32 . This is consistent with the flow dynamics data presented in Part 1 of this work, where flow velocities scaled well across the rotational speeds investigated ( N = 75–120 rpm), suggesting the mean flow was fully developed and exhibits a turbulent regime…”

Section: Resultsmentioning

confidence: 79%

Flow, suspension and mixing dynamics in DASGIP bioreactors, Part 2

2020

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This work aims to characterize the mixing and suspension dynamics occurring within two commercially available DASGIP bioreactor configurations, equipped with a twoblade paddle impeller with large impeller to tank diameter ratio, D/T = 0.97. Both continuous and intermittent agitation modes were employed to determine the impact that agitation strategy has upon mass transfer and microcarrier settling/suspension. This paper builds upon the flow dynamics data presented in Part 1 for a flat bottom DASGIP bioreactor and shows how intermittent agitation can break-up regions of slow mixing observed during continuous agitation, therefore substantially increasing the mixing efficiency of the system. Similarly, it was found that microcarrier characteristics might significantly affect the level of suspension when the impeller is in dwell status when intermittent agitation modes are used.

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“…A frequently observed mixing problem in conventional stirred tank geometries is the presence of segregated or low circulation regions at the upper section of the tank. A recent contribution [38] demonstrates that Reynolds numbers above 300,000 (based on the impeller diameter and speed) are needed to assure fully turbulent regimes in the upper third section of typical stirred tank configurations. In non-Newtonian system, this mixing pathology is even more evident under certain conditions.…”

Section: Resultsmentioning

confidence: 99%

Studying Mixing in Non-Newtonian Blue Maize Flour Suspensions Using Color Analysis

et al. 2014

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BackgroundNon-Newtonian fluids occur in many relevant flow and mixing scenarios at the lab and industrial scale. The addition of acid or basic solutions to a non-Newtonian fluid is not an infrequent operation, particularly in Biotechnology applications where the pH of Non-Newtonian culture broths is usually regulated using this strategy.Methodology and FindingsWe conducted mixing experiments in agitated vessels using Non-Newtonian blue maize flour suspensions. Acid or basic pulses were injected to reveal mixing patterns and flow structures and to follow their time evolution. No foreign pH indicator was used as blue maize flours naturally contain anthocyanins that act as a native, wide spectrum, pH indicator. We describe a novel method to quantitate mixedness and mixing evolution through Dynamic Color Analysis (DCA) in this system. Color readings corresponding to different times and locations within the mixing vessel were taken with a digital camera (or a colorimeter) and translated to the CIELab scale of colors. We use distances in the Lab space, a 3D color space, between a particular mixing state and the final mixing point to characterize segregation/mixing in the system.Conclusion and RelevanceBlue maize suspensions represent an adequate and flexible model to study mixing (and fluid mechanics in general) in Non-Newtonian suspensions using acid/base tracer injections. Simple strategies based on the evaluation of color distances in the CIELab space (or other scales such as HSB) can be adapted to characterize mixedness and mixing evolution in experiments using blue maize suspensions.

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Transition from turbulent to transitional flow in the top half of a stirred tank

Cited by 36 publications

References 84 publications

Analysis of particle cloud height dynamics in a stirred tank

Analysis of particle cloud height dynamics in a stirred tank

Flow, suspension and mixing dynamics in DASGIP bioreactors, Part 2

Studying Mixing in Non-Newtonian Blue Maize Flour Suspensions Using Color Analysis

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