Study on cavern evolution and performance of three mixers in agitation of yield-pseudoplastic fluids

Fractal perforating impeller was introduced to minimize the stagnation zone and enlarge the well-mixed zone for the mixing process of shear-thinning fluids with yield stress in a stirred reactor. The mixing performance of the fractal perforating impeller was investigated by applying experimental analyses and numerical simulation. The results showed that the fractal spaces introduced in the impeller blades provided a reduction in power consumption and an improvement in mixing efficiency compared with standard ones, and the mixing efficiency and the energy-saving effect continued to improve with the increase of the fractal iteration number of fractal spaces in the impeller blades. The fractal-3 perforating impeller reduced about 27.92, 25.87, and 12.56% of power consumption compared with a Rushton turbine, fractal-1 perforating impeller, and fractal-2 perforating impeller at Re y = 128, respectively. Meanwhile, the fractal-3 perforating impeller decreased about 22.06, 18.18, and 8.25% of the mixing time compared with a Rushton turbine, fractal-1 perforating impeller, and fractal-2 perforating impeller at P v = 0.45 kW·m–3, respectively. In addition, the introduction of fractal spaces in the impeller blades could reduce the size of the trailing vortex and destroy the recirculation zone compared with standard ones, and this helped reduce the energy consumed at the tailing vortices and dedicate more energy to fluid mixing. A desired result was obtained that the design of a fractal perforating impeller could expand the high-velocity region and enlarge the size of the cavern compared with a Rushton turbine and increasingly so with the increase of the fractal iteration number of fractal spaces in the impeller blades.

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“…For radial flow impeller, k s = 11.5. 26,28,29 The apparent viscosity (η) of the xanthan gum solution can be expressed as 24−26…”

Section: Physical Systemmentioning

confidence: 99%

Mixing Characteristics of Shear-Thinning Fluids in a Fractal Perforating Impeller Stirred Reactor

Yang

Xie

2023

Ind. Eng. Chem. Res.

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“…The rheological parameters of xanthan gum solution are shown in Table 1. 34 Metzner and Otto's correlation can be utilized to calculate the average shear rate 31−33 k N…”

Section: Physical Systemmentioning

confidence: 99%

“…The xanthan gum solution served as the operational fluid, and the rheological properties of this fluid, which exhibits shear-thinning behavior and yield stress, can be depicted by the Herschel–Bulkley model − τ = τ normaly + K γ̇ n where τ y is the yield stress, K is the consistency index, n is the flow behavior index, and γ̇ n is the shear rate. The rheological parameters of xanthan gum solution are shown in Table …”

Section: Physical Systemmentioning

confidence: 99%

Investigation on Solid Particles and Pseudoplastic Fluid Mixing Characteristics in a Dislocated Self-Similarity Impeller Stirred Reactor

Wang

Yang

et al. 2023

Ind. Eng. Chem. Res.

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A dislocated self-similarity impeller (DS impeller) was introduced in the solid particles and pseudoplastic fluid mixing process. The investigation on the mixing performance of a dislocated pitched-blade impeller (DPB impeller) and a DS impeller was conducted by applying experimental and computational fluid dynamics simulation. Results showed that the DS impeller could enlarge cavern zones and improve the uniformity of solid particle distribution compared with the DPB impeller at an equivalent power consumption (P), and these effects could be further enhanced by increasing the self-similar iteration number of the DS impeller. Meanwhile, the DS impeller could decompose trailing vortices into smaller ones, destroy the recirculation zone, consume less power consumption (P), and decrease the power number (N p ) through the self-similar structure design of impeller blades, and the impeller energy utilization rate of the DS impeller could be improved by increasing the self-similar iteration number. The DS-2 impeller reduced about 40.56 and 13.50% of power consumption compared with those of the DPB impeller and DS-1 impeller at Re y = 236, respectively. This indicated that the implementation of a self-similar structure design for impeller blades could effectually enlarge the well-mixed regions and improve the mixing effectiveness in the solid particles and pseudoplastic fluid mixing process, and with a greater effect obtained as the number of self-similar iterations increased.

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“…This phenomenon is particularly notable within laminar and transitional flow regimes [12]. To address these issues, several studies demonstrated that intensifying operational conditions such as the impeller rotational speed and the aeration rate could positively influence mixing performance and offset the rise in broth viscosity [5,13]. In contrast, Jamshidzadeh et al [14] reported instances of flooding and poor mixing patterns arising from higher aeration rates.…”

Section: Introductionmentioning

confidence: 99%

Analyzing Local Shear Rate Distribution in a Dual Coaxial Mixing Bioreactor Handling Herschel–Bulkley Biopolymer Solutions through Computational Fluid Dynamics

Sharifi,

Behzadfar,

Ein-Mozaffari

2023

Processes

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For the aeration of highly viscous non-Newtonian fluids, prior studies have demonstrated the improved efficacy of dual coaxial mixing bioreactors fitted with two central impellers and a close clearance anchor. Evaluating the effectiveness of these bioreactors involves considering various mixing characteristics, with a specific emphasis on shear rate distribution. The study of shear rate distribution is critical due to its significant impact on the mixing performance, gas dispersion, and homogeneity in aerated mixing systems comprising shear-thinning fluids. Although yield-pseudoplastic fluids are commonly employed in various industries, there is a research gap when it comes to evaluating shear rate distribution in aerated mixing bioreactors that utilize this fluid type. This study aims to investigate shear rate distribution in an aerated double coaxial bioreactor that handles a 1 wt% xanthan gum solution, known as a Herschel–Bulkley fluid. To achieve this goal, we employed an experimentally validated computational fluid dynamics (CFD) model to assess the effect of different mixing configurations, including down-pumping and co-rotating (Down-Co), up-pumping and co-rotating (Up-Co), down-pumping and counter-rotating (Down-Counter), and up-pumping and counter-rotating (Up-Counter) modes, on the shear rate distribution within the coaxial mixing bioreactor. Our findings revealed that the Up-Co system led to a more uniform local shear distribution and improved mixing performance.

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Study on cavern evolution and performance of three mixers in agitation of yield-pseudoplastic fluids

Cited by 8 publications

References 41 publications

Mixing Characteristics of Shear-Thinning Fluids in a Fractal Perforating Impeller Stirred Reactor

Mixing Characteristics of Shear-Thinning Fluids in a Fractal Perforating Impeller Stirred Reactor

Investigation on Solid Particles and Pseudoplastic Fluid Mixing Characteristics in a Dislocated Self-Similarity Impeller Stirred Reactor

Analyzing Local Shear Rate Distribution in a Dual Coaxial Mixing Bioreactor Handling Herschel–Bulkley Biopolymer Solutions through Computational Fluid Dynamics

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