Break‐Up of Nanoparticle Agglomerates by Hydrodynamically Limited Processes

Xie, Liansong; Rielly, Chris D.; Özcan-Taşkın, N. Gül

doi:10.1080/01932690701729211

Cited by 25 publications

(16 citation statements)

References 10 publications

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“…During the course of processing, the PSD had a distinctive bi-modal feature with both of the batch rotor-stators ( Figures 5 and 6). This is in line with previously reported findings with this material using inline rotor-stators or valve homogenisers (Baldyga et al, 2008a;Özcan-Taskin et al, 2009 andXie et al, 2008). Due to this bi-modal size distribution, using an overall mean diameter can hide important features of the dispersion.…”

Section: Resultssupporting

confidence: 79%

“…Different process devices used for the purpose include the stirred bead mill (Stenger et al, 2005;Kowalski et al, 2008;Schilde et al, 2010), ultrasonic dispersers (Baldyga et al, 2008b(Baldyga et al, , 2009Quarch et al, 2010) in-line rotor-stators (Baldyga et al, 2008a;Padron et al, 2008;Özcan-Taşkın et al, 2016), a batch rotor-stator or high pressure devices (Sauter and Schuchmann, 2007;Seekkuarachchi et al, 2008 andXie et al, 2008). Local energy dissipation rate in these devices, responsible for the breakup of agglomerates, can be orders of magnitude higher than the average energy dissipation rate.…”

Section: Introductionmentioning

confidence: 99%

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Dispersion of clusters of nanoscale silica particles using batch rotor-stators

Kamaly

Tarleton

Özcan-Taşkın

2017

Advanced Powder Technology

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Nanoparticle powders added into a liquid medium form structures which are much larger than the primary particle size (aggregates and agglomerates)-typically of the order of 10's of microns. An important process step is therefore the deagglomeration of these clusters to achieve as fine a dispersion as possible. This paper reports the findings of a study on the dispersion of hydrophilic fumed silica nanoparticle clusters, Aerosil 200V, in water using two batch rotor-stators: MICCRA D-9 and VMI. The MICCRA D-9 head consists of a set of teeth for the stator and another for the rotor, whereas the VMI has a stator with slots and a rotor which consists of a 4-bladed impeller attached to an outer set of teeth. The dispersion process, studied at different power input values and over a range of concentrations (1, 5, 10 wt.%), was monitored through the evolution of PSD. Erosion was found to be the dominant breakage mechanism irrespective of operating conditions or rotor-stator type. The smallest attainable size was also found to be independent of the power input or the design of the rotor-stator. Break up kinetics increased upon the increase of power input, and this also depended on the rotor-stator design. With MICCRA D-9 which has smaller openings on both the stator and rotor, the break up rate was faster. Increasing the particle concentration decreased break up kinetics. It could also be shown that operating at high concentrations can still be beneficial as the break up rate is higher when assessed on the basis of specific power input per mass of solids.

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Section: Resultssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

Kamaly

Tarleton

Özcan-Taşkın

2017

Advanced Powder Technology

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“…The maximum dissipation rate may deviate significantly from the mean, which may determine, for instance, the minimum drop size in dispersed gas or liquid flows (Zhou and Kresta, 1996), and the rate of fines generation in nano-particle dispersions (Xie et al, 2008). After processing the stereo-PIV velocity fields using a global standard deviation filter, and applying the LES analogy of Sheng et al (2000) to the 3-D data, and Kresta (1996).…”

Section: Ratios Of Maximum and Mean Energy Dissipationmentioning

confidence: 99%

“…The local dissipation rate,  , is of particular interest, as it is a key variable related to the breakage of nano-particle clusters (Xie et al, 2008). The calculation of  has been the subject of many previous works (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, a study has been carried out to investigate the flow field and turbulence properties generated by an EkatoMizer, which is a type of sawtooth impeller. Recently, studies have been carried out to investigate the dispersion of nano-particle agglomerates by a sawtooth impeller (Xie et al, 2007;Xie et al, 2008), but the present contribution focuses on the local hydrodynamics of the flow close to the rotating blades.…”

Section: Introductionmentioning

confidence: 99%

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PIV study of the flow field generated by a sawtooth impeller

Unadkat

Rielly

Nagy

2011

Chemical Engineering Science

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Stereoscopic and high-speed particle image velocimetry (PIV) techniques have been employed to study the flow field induced by a sawtooth (EkatoMizer) impeller, operated in the fully turbulent flow regime at an impeller speed of 1500 rpm.Ensemble-averaged mean flow fields and turbulence quantities were calculated for a region close to the impeller blades. The flow was found to be anisotropic near the impeller and exhibited return-to-isotropy behaviour further away from it. Macroinstabilities were found to have a high probability of occurrence in the discharge stream. All three velocity components from the stereo-PIV measurements were used to estimate the dissipation rate, by adopting a large eddy simulation (LES) analogy.Spurious vectors distorting the dissipation rate calculation were identified, and various standard deviation filters were applied for vector validation. By evaluating the filtered dissipation rate profiles against the multi-fractal intermittency model of Meneveau and Sreenivasan (1991), the global standard deviation filter was found to be the most suitable type. The ratio of the maximum to the mean dissipation rate for the EkatoMizer discharge stream was found to be similar to that reported for Rushton disk turbine and pitched-blade turbine impellers in the literature, raising questions about the reported high-shear advantage of sawtooth impellers.

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Performance Evaluation of Two High‐Shear Impellers in an Unbaffled Stirred Tank

et al. 2015

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High-shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquids and break down particle agglomerates. A detailed numerical study of two commercial ring-style HSIs of laboratory scale was carried out and their performance was compared with the Rushton turbine (RT). It was found that power and pumping numbers or their ratio cannot be simply connected for properly selecting an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume to the mean in the entire volume at two constant values of power input turned out to be lower for HSIs compared to that evaluated for RT. However, at higher power input, the dimensionless average viscous dissipation in the blade swept volume was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.

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Break‐Up of Nanoparticle Agglomerates by Hydrodynamically Limited Processes

Cited by 25 publications

References 10 publications

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

PIV study of the flow field generated by a sawtooth impeller

Performance Evaluation of Two High‐Shear Impellers in an Unbaffled Stirred Tank

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