Flow Patterns in Rheologically Evolving Model Fluids Produced by Hybrid Dual Mixing Systems

Espinosa-Solares, Teodoro; Fuente, Edmundo Brito-de la; Tecante, Alberto; Tanguy, P. A.

doi:10.1002/1521-4125(200109)24:9<913::aid-ceat913>3.0.co;2-h

Cited by 27 publications

(3 citation statements)

References 14 publications

(13 reference statements)

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“…By adding a wall scraping impeller, such as an anchor, to the system consisting of one or more central impellers, due to the synergistic effects of the impellers the flow patterns change significantly [47]. According to Espinosa et al, these flow patterns are a function of the speed ratio of the impellers (𝑅 𝑁 = high speed (central impeller)/low speed (anchor)) [47]. In co-axial configurations (central impeller and anchor), two extreme conditions happen, namely low-speed ratio and high-speed ratio.…”

Section: Flow Patterns In Gas Dispersionmentioning

confidence: 99%

Investigation of Local and Overall Volumetric Mass Transfer Coefficient and Gas Holdup in Aerated Coaxial Mixing Systems Containing Non-Newtonian Fluids through Tomography and Computational Fluid Dynamics

Jamshidzadeh

2024

Preprint

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Gas dispersion in Newtonian and non-Newtonian fluids is one of the most important processes in biochemical industries. Aerated mixing tanks are preferred due to their superior performance in increasing the contact area and mass transfer between two phases. To enhance the operation of aerated mixing tanks, especially in the presence of non-Newtonian fluids, a configuration consisting of two central impellers and a wall scraping anchor is recommended. In this study, the performance of the coaxial system for gas dispersion in a non-Newtonian fluid was investigated using electrical resistance tomography (ERT), and computational fluid dynamics (CFD). For the first time, the effects of the central and anchor impeller speed, air flow rate, rheology, impeller type, pumping direction, and anchor rotation mode were studied on the performance of coaxial mixers comprised of two central impellers at the presence of a pseudoplastic fluid in terms of local and overall gas hold-up, bubble size, and volumetric mass transfer coefficient (kLa). Modified correlations were proposed for the power number and Reynolds number of the aerated coaxial systems. Additionally, empirical correlations for power consumption, overall gas holdup, and volumetric mass transfer coefficient of the coaxial mixer were also developed. The results showed the downward pumping co-rotation mode of the pitched blade impellers resulted in the highest gas holdup, while the numerical simulations revealed a non- uniform distribution of the gas phase in the system with the pitched blade impeller in the downward pumping mode. It was further discovered that the Sauter mean bubble size increased with the fluid concentration resulting in a lower amount of interfacial area, and consequently decreasing the kLa of the system. A comparison between the results of local and overall kLa revealed the superiority of the coaxial mixing system furnished with Rushton turbines. The results of this study lead to the development of: (i) new approaches, based on the local distribution of the gas holdup and kLa, to characterize aerated coaxial mixing tanks and evaluate coaxial mixers performance; (ii) a modified correlation for equivalent speed and diameter of the coaxial mixers; and (iii) empirical correlations that can be used for scaleup purposes.

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Section: Flow Patterns In Gas Dispersionmentioning

confidence: 99%

Investigation of Local and Overall Volumetric Mass Transfer Coefficient and Gas Holdup in Aerated Coaxial Mixing Systems Containing Non-Newtonian Fluids through Tomography and Computational Fluid Dynamics

Jamshidzadeh

2024

Preprint

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“…Espinosa‐Solares et al [ 15 ] observed effective gas dispersion in both Newtonian and non‐Newtonian fluids using a coaxial mixer comprised of a helical ribbon and a Smith turbine. The high efficiency of coaxial mixers in dispersing gas was further confirmed in aerated mixing systems with viscous Newtonian fluids through numerical simulations and electrical resistance tomography (ERT) measurements.…”

Section: Introductionmentioning

confidence: 99%

“…[8][9][10] Therefore, coaxial mixers have been extensively investigated as an effective alternative in increasing the well-mixed regions since their configuration combines a high-speed central impeller and a close clearance impeller rotating at a lower speed. [11][12][13][14] Espinosa-Solares et al [15] observed effective gas dispersion in both Newtonian and non-Newtonian fluids using a coaxial mixer comprised of a helical ribbon and a Smith turbine. The high efficiency of coaxial mixers in dispersing gas was further confirmed in aerated mixing systems with viscous Newtonian fluids through numerical simulations and electrical resistance tomography (ERT) measurements.…”

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confidence: 99%

Effect of agitation and aeration on gas dispersion efficiency in coaxial mixers containing yield‐pseudoplastic fluids: Experimental and numerical analysis

Barros,

Ein‐Mozaffari,

Lohi

2023

Can J Chem Eng

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Aerated stirred vessels are commonly employed to enhance gas dispersion. However, the associated high energy consumption is a challenging feature, particularly when dealing with complex non‐Newtonian fluids. Coaxial mixers comprising a central impeller and a close‐clearance impeller have emerged as an energy‐efficient alternative that effectively intensifies gas dispersion. Hence, the objective of this study is to investigate the effect of aeration and agitation on the gas dispersion effectiveness of a coaxial mixer containing a yield‐pseudoplastic fluid. An anchor‐pitched blade turbine was employed to disperse air into a 1 wt.% xanthan gum solution, and the analysis primarily focused on characterizing the gas holdup and fluid flow behaviour. Gas holdup data were obtained experimentally using electrical resistance tomography (ERT), while computational fluid dynamics (CFD) simulations provided a detailed analysis of fluid flow patterns within the coaxial mixer. The rotational speed of the impeller exhibited a non‐monotonic effect on the gas holdup, and a significant influence of the interaction between variables was identified. For instance, the experimental data showed that the aeration effect varied with the anchor speed. Nevertheless, the variables' interaction effect was explained by the change in flow pattern observed numerically. Furthermore, the CFD results demonstrated that high gas holdup does not necessarily indicate intensified mixing. Therefore, combining experimental data and numerical simulations enables a more accurate characterization of mixing performance. These findings contribute to the understanding and improvement of mixing performance in such a complex system, which is crucial for designing efficient operations.

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Pullulan, Microbial Production Methods

Yang

Thibault

LeDuy

2010

Encyclopedia of Industrial Biotechnology

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Pullulan is a water‐soluble polysaccharide produced through fermentation with Aureobasidium pullulans . Pullulan has been used as specialty food for decades in Japan. Owing to its relatively high price, recent developments on pullulan are mainly focused on its application in biomedical engineering and pharmaceutical industry. Both laboratory and commercial pullulan production methods are reviewed. Among several problems associated with pullulan fermentation, the highly viscous fermentation broth remains the biggest challenge. The viscous non‐Newtonian broth creates major difficulties in mixing, oxygenation, process monitoring, sampling, and downstream product recovery. Many approaches to improve the fermentation efficiency have been attempted. One promising method is to use close clearance impellers, such as reciprocating plate mixer, instead of standard Rushton turbines in order to achieve more uniform mixing. Other unconventional techniques, such as cell immobilization, hyperbaric fermentation, and nonsterile fermentation, have also been discussed. However, these technologies need more research and investigation before they can be implemented at an industrial scale.

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Flow Patterns in Rheologically Evolving Model Fluids Produced by Hybrid Dual Mixing Systems

Cited by 27 publications

References 14 publications

Investigation of Local and Overall Volumetric Mass Transfer Coefficient and Gas Holdup in Aerated Coaxial Mixing Systems Containing Non-Newtonian Fluids through Tomography and Computational Fluid Dynamics

Investigation of Local and Overall Volumetric Mass Transfer Coefficient and Gas Holdup in Aerated Coaxial Mixing Systems Containing Non-Newtonian Fluids through Tomography and Computational Fluid Dynamics

Effect of agitation and aeration on gas dispersion efficiency in coaxial mixers containing yield‐pseudoplastic fluids: Experimental and numerical analysis

Pullulan, Microbial Production Methods

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