Measurement of maximum stable drop size in aerated dilute liquid–liquid dispersions in stirred tanks

Daub, Adrian; Böhm, Melanie; Delueg, S.; Büchs, Jochen

doi:10.1016/j.ces.2013.08.023

Cited by 12 publications

(7 citation statements)

References 37 publications

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“…The maximum stable particle diameter is the minimum particle diameter that resists breaking further in turbulent flow field. In liquid–liquid dispersions the existence of a maximum stable drop size is generally accepted . Particles smaller than a critical size, namely

d_{\max}

, can be resisted the flow field without undergoing breakage, but the larger ones are unstable and eventually break up.…”

Section: Breakup Modeling—literature Reviewmentioning

confidence: 99%

Theoretical model for multiple breakup of fluid particles in turbulent flow field

Razzaghi

2016

AIChE Journal

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Generalized phenomenological model, based on the theories of probability and isotropic turbulence, is developed for multiple breakup of fluid particles in turbulent flow field. The approach uses a series of successive binary breakup events occur at a time scale comparable to the colliding eddy turnover time. It was found that the use of energy density, instead of energy, will increase the predicted binary breakup rate which is usually underestimated by the existing models in the literature. Generalization of the binary breakup model for multiple fragmentations is performed by defining a “remaining energy function” for the colliding eddy which means the contribution of original eddy to the later breakup events. For ternary breakage, the model shows a reasonably good agreement with the experimental data. The quaternary fragmentation frequency, however, is of negligible importance at lower energy dissipation rates but its contribution to breakage fraction at higher energy dissipation rates becomes considerable. The results also show that ternary and quaternary breakups have a considerable 90% contribution to the overall fragmentation, while pentenary and further fragmentations are of lower importance at low energy dissipation rates. At higher levels of energy dissipation rate, fragmentations up to six daughter particles contribute to more than 95% of the overall fragmentations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4508–4525, 2016

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d_{\max}

, can be resisted the flow field without undergoing breakage, but the larger ones are unstable and eventually break up.…”

Section: Breakup Modeling—literature Reviewmentioning

confidence: 99%

Theoretical model for multiple breakup of fluid particles in turbulent flow field

Razzaghi

2016

AIChE Journal

View full text Add to dashboard Cite

show abstract

“…The maximum stable drop sizes measured were essentially constant during this time span in all reactors. Examples for this were shown in Daub et al [ 25 ]. Extending the experimental time to up to 9 h yielded a further decrease of the maximum stable drop size in the range of 10% compared to the value at 3 h dispersion time in the 3 m 3 reactor.…”

Section: Resultsmentioning

confidence: 88%

“…Very small drops in the range < 50 μm are also present that might be daughter drops that developed during break up of larger drops and did not coalesce to larger droplets any more. These small droplets are not relevant for the subject of this work as described in [ 9 ] and [ 25 ]. Table 3 compares characteristic values for the main peaks of the distributions that were calculated from the fitted normal distributions.…”

Section: Resultsmentioning

confidence: 99%

“…For all reactor configurations, including the 40 m 3 reactor, the values are below the standard deviation of d max for independent experiments which was determined to approx. 10% [ 25 ]. That means the deviation between measurement and model has a similar magnitude as the deviation between independent experiments.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, a method was established to measure hydromechanical stress that can be applied in large scale equipment at intense agitation and aeration. Details on the development of the measurement method are specified in Daub et al [ 25 ]. The method is based on the theory of turbulent drop dispersion and uses the well established correlation of the maximum stable drop size d max with maximum local energy dissipation rate ϵ max for break-up controlled dispersions:…”

Section: Introductionmentioning

confidence: 99%

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Characterization of hydromechanical stress in aerated stirred tanks up to 40 m3 scale by measurement of maximum stable drop size

et al. 2014

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BackgroundTurbulence intensity, or hydromechanical stress, is a parameter that influences a broad range of processes in the fields of chemical engineering and biotechnology. Fermentation processes are often characterized by high agitation and aeration intensity resulting in high gas void fractions of up to 20% in large scale reactors. Very little experimental data on hydromechanical stress for such operating conditions exists because of the problems associated with measuring hydromechanical stress under aeration and intense agitation.ResultsAn indirect method to quantify hydromechanical stress for aerated operating conditions by the measurement of maximum stable drop size in a break-up controlled dispersion was applied to characterize hydromechanical stress in reactor scales of 50 L, 3 m3 and 40 m3 volume with a broad range of operating conditions and impeller geometries (Rushton turbines). Results for impellers within each scale for the ratio of maximum to specific energy dissipation rate ϕ based on measured values of maximum stable drop size for aerated operating conditions are qualitatively in agreement with results from literature correlations for unaerated operating conditions. Comparison of data in the different scales shows that there is a scale effect that results in higher values for ϕ in larger reactors. This behavior is not covered by the classic theory of turbulent drop dispersion but is in good agreement with the theory of turbulence intermittency. The data for all impeller configurations and all aeration rates for the three scales can be correlated within ±20% when calculated values for ϕ based on the measured values for dmax are used to calculate the maximum local energy dissipation rate. A correlation of the data for all scales and all impeller configurations in the form ϕ = 2.3∙(ϕunaerated)0.34∙(DR)0.543 is suggested that successfully models the influence of scale and impeller geometry on ϕ for aerated operating conditions.ConclusionsThe results show that besides the impeller geometry, also aeration and scale strongly influence hydromechanical stress. Incorporating these effects is beneficial for a successful scale up or scale down of this parameter. This can be done by applying the suggested correlation or by measuring hydromechanical stress with the experimental method used in this study.

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2018

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Measurement of maximum stable drop size in aerated dilute liquid–liquid dispersions in stirred tanks

Cited by 12 publications

References 37 publications

Theoretical model for multiple breakup of fluid particles in turbulent flow field

Theoretical model for multiple breakup of fluid particles in turbulent flow field

Characterization of hydromechanical stress in aerated stirred tanks up to 40 m3 scale by measurement of maximum stable drop size

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