On the efficiency of turbulent mixing in rotating stirrers

Trivellato, F.

doi:10.1016/j.cep.2011.05.012

Cited by 12 publications

(10 citation statements)

References 25 publications

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“…For instance, the peak dissipation rate for vessels stirred by Rushton turbines is 25–30 times higher in the immediate impeller region compared to the mean dissipation rate, causing an estimated 60% of the total energy input to be dissipated there . As a result, relatively stagnant regions are created in the rest of the tank, inhibiting complete homogenization and increasing mixing times …”

Section: Introductionmentioning

confidence: 99%

“…A further issue with mixing turbines, especially of the radial type, is the strong localized shear in the impeller discharge region, connected with the tip vortices emanating from the blades . This may create problems in applications where cell membranes and micro‐organisms are involved or destroy shear sensitive cells …”

Section: Introductionmentioning

confidence: 99%

“…To address the above issues, extensive research has been centered during the last decades on impeller blade geometry modification . This procedure, mainly done by trial and error, has produced countless impeller types with documented flow fields.…”

Section: Introductionmentioning

confidence: 99%

“…This procedure, mainly done by trial and error, has produced countless impeller types with documented flow fields. The actual improvement however is suggested to be modest at best . This underlines the importance of introducing new designs which can contribute to promising results in terms of mixing efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Power consumption and form drag of regular and fractal‐shaped turbines in a stirred tank

et al. 2016

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Previous wind-tunnel measurements have shown that fractal shaped plates have increased drag compared to square plates of the same area. In this study we measure the power consumption and drag of turbines with fractal and rectangular blades in a stirred tank. Power number decreases from rectangular to fractal impellers by over 10%, increasingly so with fractal iteration number. Our results suggest that this decrease is not caused by the wake interaction of the blades, nor solely by the wake interaction with the walls either.Pressure measurements on the blades' surface show that fractal blades have lower drag than the rectangular ones, opposite to the wind tunnel experiment results. All tested blades' centre of pressure radius increases with Re, while their drag coefficient decreases, a possible effect of the solid body rotation increase with Re. Spectral analysis of the pressure signal reveals two peaks possibly connected to the blades' roll vortices.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Power consumption and form drag of regular and fractal‐shaped turbines in a stirred tank

et al. 2016

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“…Modification of blade design has been considered as a means to achieve this objective. Indeed this has been the subject of extensive research in the past decades, but these efforts yielded only modest improvements …”

Section: Introductionmentioning

confidence: 99%

Reduced power consumption in stirred vessels by means of fractal impellers

2018

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Earlier studies have shown that the power consumption of an unbaffled stirred vessel decreases significantly when the regular blades are replaced by fractal ones. In this paper, the physical explanation for this reduction is investigated using Direct Numerical Simulations at Re = 1600. The gaps around the fractal blade perimeter create jets that penetrate inside the recirculation zone in the wake and break up the trailing vortices into smaller ones. This affects the time‐average recirculation pattern on the suction side. The volume of the separation region is 7% smaller in the wake of the fractal blades. The lower torque of the fractal impeller is equivalent to a decreased transport of angular momentum; this difference stems from the reduced turbulent transport induced by the smaller trailing vortices. The major difference in the turbulent dissipation is seen in the vicinity of trailing vortices, due to fluctuations of velocity gradients at relatively low frequencies. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1485–1499, 2018

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