Critical analysis of Zwietering correlation for solids suspension in stirred tanks

Ayranci, İnci; Kresta, Suzanne M.

doi:10.1016/j.cherd.2013.09.005

Cited by 54 publications

(32 citation statements)

References 18 publications

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“…By examining the N js of a wide range of particles at different concentrations in six sizes of flat‐based baffled tanks with different impeller types, Zwietering proposed a method for correlating the data using dimensional analysis. However, Ayranci and Kresta critically analyzed Zwietering's data treatment and reported that it was only appropriate for solids concentrations up to 2 wt %. Other researchers concluded that N js predicted by Zwietering's method was much higher than the N js as they have measured .…”

Section: Introductionmentioning

confidence: 99%

Quantitative Measurements of the Critical Impeller Speed for Solid‐Liquid Suspensions

Nienow

Alberini

2019

Chem Eng & Technol

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A quantitative methodology for particle suspension assessment is presented. A new parameter, f mov/tot , the ratio of the mean number of moving particles to the total number of particles, is introduced to evaluate the minimum speed required to just suspend solids. This approach is tested to investigate the impact of impeller clearance on the minimum impeller speed, N js , in a vessel when using a radial flow Rushton turbine. Flow patterns and power numbers obtained experimentally and computationally support the suspension findings. Image analysis is an appropriate method for determining N js . Lowering the impeller clearance reduces the speed required for particle suspension with a change of flow pattern from a radial discharge with two loops to a single loop scouring the vessel base. The power number also falls markedly at the two-to-one loop transition as does the strain rate near the base.

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Section: Introductionmentioning

confidence: 99%

Quantitative Measurements of the Critical Impeller Speed for Solid‐Liquid Suspensions

Nienow

Alberini

2019

Chem Eng & Technol

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“…However, more recently, Kresta et al [19] found that there was no clear pattern in N js upon changing the viscosity and suggested that N js is independent of viscosity in turbulent flow when the particles are larger than the Kolmogorov length scale. Effects due to the particle and fluid densities are generally well understood and agreed upon, as noted in the work of Ayranci and Kresta [20]. There has been considerable research into the effects of particle diameter on N js , in both mono-and poly-dispersed systems, generally agreeing on Zwietering's exponent [4,21,22].…”

Section: A Brief Review Of Prior Workmentioning

confidence: 79%

“…Recent works have raised questions over the validity of the effect that solids loading has on just-suspended speed. Ayranci and Kresta [20], e.g., reported that their data was not accurately correlated by the 0.13 exponent of Zwietering, who studied relatively low solids loadings ranging from 0.5 to 17 wt % (0.5 X 20) [6]. Ayranci and Kresta performed experiments up to 35.5 wt % (X = 55) and recommended that the exponent is changed to 0.24.…”

Section: A Brief Review Of Prior Workmentioning

confidence: 99%

Positron Emission Particle Tracking for Liquid‐Solid Mixing in Stirred Tanks

et al. 2020

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Mixing in stirred tanks is vital to a wide range of industrial processes, typically requiring solids to be fully suspended and evenly distributed. The quality of suspension and mixing is typically measured visually. Such measurements are thus subject to human interpretation and can only feasibly be conducted in transparent systems – an uncommon condition in industrial systems. Visual measurements of homogeneity must also infer full 3D distributions of particles solely from the observation of a limited section thereof. This work details methods by which a system's homogeneity and state of suspension may be measured and quantified with no human interpretation, which can extract information from opaque systems and consider full 3D data acquired throughout the interior of a given system.

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“…The exponent on solid concentration in Zwietering correlation was confirmed by Nienow (1968) and Baldi et al, (1978). Ayranci and Kresta (2014) reported that the existing Zwietering equation is applicable for the solid concentration value up to 2 % (w/w) solids. They modified the Zwietering correlation, with the new exponent on concentration, which provides predictions up to 35 % (w/w).…”

Section: Introductionmentioning

confidence: 79%

Effect of Impeller Clearance and Liquid Level on Critical Impeller Speed in an Agitated Vessel using Different Axial and Radial Impellers

Devarajulu

Muruganandam

2016

JAFM

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The effect of impeller clearance and liquid level on the critical impeller speed (Njs) for various radial and axial flow impellers in 0.29 m ID agitated vessel has been studied. Five types of radial impellers: Rushton turbine (RT), Straight blade (SB), Curved blade (CB), Curved blade with disc (CBWD) and R130 impeller and four types of axial impellers: Rushton turbine 45 o angle (RT 45), Pitched blade (PBT), A320 and HE3 impeller were used. Tap water and resin particle of 0.506 mm were used as liquid and solid phases, respectively. The impeller clearance to vessel diameter (T) was varied between 0.17 and 0.41. The liquid level (H) was also varied as H/T=0.5, H/T=0.75 and H/T=1. The R130 impeller and A320 impeller was found to be more efficient among radial and axial impellers respectively. A new expression for Zwietering constant 'S' was developed to predict critical impeller speed, considering impeller clearance and liquid level for all the impellers. The results obtained here show that the 'S' values increase with increase in clearance, and decrease with liquid level for all impellers and it also depends on the type of impeller.

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Critical analysis of Zwietering correlation for solids suspension in stirred tanks

Cited by 54 publications

References 18 publications

Quantitative Measurements of the Critical Impeller Speed for Solid‐Liquid Suspensions

Quantitative Measurements of the Critical Impeller Speed for Solid‐Liquid Suspensions

Positron Emission Particle Tracking for Liquid‐Solid Mixing in Stirred Tanks

Effect of Impeller Clearance and Liquid Level on Critical Impeller Speed in an Agitated Vessel using Different Axial and Radial Impellers

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