On impeller circulation and mixing effectiveness in the turbulent flow regime

Nienow, Alvin W.

doi:10.1016/s0009-2509(97)00072-9

Cited by 298 publications

(214 citation statements)

References 11 publications

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“…As is apparent from Figures 6 and 7b, its extent decreases with an increase in Q G at high agitator speeds, whereas a partial reversal of this effect takes place at low N. These facts can be explained with the hampering effect of the gas bubbles on liquid mixing at high rotational speed and the competition between stirring and aeration in determining the state of mixing at lower speeds. 33 Despite this, the full symptoms of flooding were not recognizedsnot even at the highest Q G and the lowest N values investigated in this paper.…”

Section: Influence Of the Working Conditions Andmentioning

confidence: 61%

Analysis of the Fluid Dynamic Behavior of the Liquid and Gas Phases in Reactors Stirred with Multiple Hydrofoil Impellers.

Pinelli¹,

Magelli²

2000

Ind. Eng. Chem. Res.

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Liquid-and gas-phase macromixing behavior was studied in gas-liquid high-aspect-ratio reactors stirred with multiple hydrofoil impellers pumping downward. Water, a sodium sulfate solution, and poly(vinylpyrrolidone) solutions of viscosity up to 110 mPa‚s were used as the liquid. For characterizing the liquid phase, mixing time experiments were conducted at various operating conditions, while detecting the response curves at several positions inside the tank. Comparison of the experimental curves with the theoretical ones provided by simple fluid dynamic models showed that the axial dispersion model is quite acceptable. The influence of impeller speed, gas flow rate, and viscosity on the model parameter was studied, and dimensionless relationships are given. The gas behavior was studied by means of the RTD and modeled with the axial dispersion model, which proved good for water and acceptable with coalescence-inhibiting electrolyte solutions. The model parameter dependence on the operating conditions was studied.Comparison between hydrofoil impellers and radial Rushton turbines is also attempted.

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Section: Influence Of the Working Conditions Andmentioning

confidence: 61%

Analysis of the Fluid Dynamic Behavior of the Liquid and Gas Phases in Reactors Stirred with Multiple Hydrofoil Impellers.

Pinelli¹,

Magelli²

2000

Ind. Eng. Chem. Res.

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“…), but also according to the various criteria for achieving the mixing rate. Thus, the mixing rate can be reached by determination: i) A = ±0.05∆A [21] and [26] or ii) A' = ±1 % [11], ±5 % [32] and [33] or even ±10 % [34] where A represents any measured property and A' its fluctuation [29]. If we proceed from the local measurements, then we have to additionally take into account the influence of the location itself (r, z, ), since the deviations between mixing times were found to be from -6 % to 11 % of the mean mixing time [11].…”

Section: Mixing Time During Liquid Mixingmentioning

confidence: 99%

“…A multi-stage impeller with a proper configuration provides the circulation of substances in the fermenter and most evenly distributes the air throughout the liquid volume [10]. To determine these conditions, it is necessary to know the main characteristics of the individual impeller, such as the mixing power [11] and [12], gas holdup [11], bubble size and distribution [13] and [14], flooding in gas-liquid systems [8], [15] and [16] and in even more complex three-phase systems [17] and [18], mixing time [19] to [21], etc.…”

Section: Introductionmentioning

confidence: 99%

“…If an additional enlarged amount of air needs to be dispersed in some fermentation processes [8], at a minimum, the lowest impeller must be replaced with a more capable one in terms of preserving the pumping capacity and the small power reduction as much as possible by gassing. There are many studies in which Rushton turbine modifications [21] and [22] and disk impellers of various blade shapes [19] and [23] to [26] were used to enhance the lowest impeller characteristics.…”

Section: Introductionmentioning

confidence: 99%

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Asymmetric Blade Disc Turbine for High Aeration Rate in a Fermenter

2018

SV-JME

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Highlights: High efficiency of the newly developed and patented asymmetrically folded blade turbine (ABT) during dispersing of air into water by single impeller stirring.  Low power number of the ABT impeller in water mixing (1.75).  High pumping capacity by air dispersing at very small power draw reduction (less than 16 %).  Capable of dispersing much greater amounts of air (up to 53 %) than the Rushton turbine is.  The shortest mixing time by the same impeller energy dissipation.  Some CFD analysis results included for better insight into inhomogeneity in the liquid. INTRODUCTIONAir dispersion in tall, slim fermenters is mostly carried out with multistage impellers to provide high air flow intake, which must be supplied in some fermentation processes in the pharmaceutical industry. Such an impeller can be assembled of two equal impellers, such as dual Rushton turbines in parallel, merging, and diverging flow conditions [1], power consumption [2], mixing rate [3] or flow patterns [4]. The higher the ratio between tank height and its diameter H/T, the higher the number of impellers equidistantly placed to ensure as much uniform void fraction distribution as possible [5] to [8]. Nowadays, a combination of axial and radial impellers [7] and [9] predominates. The choice of a proper impeller for the given geometric configuration of the mixing vessel is of prime importance for the optimal achievement in the fermentation process: a fermenter must have a flow field that provides the organisms with air throughout the entire volume of the liquid. Any dead zone can cause an improperly fermented product due to lack of air. A multi-stage impeller with a proper configuration provides the circulation of substances in the fermenter and most evenly distributes the air throughout the liquid volume [10]. To determine these conditions, it is necessary to know the main characteristics of the individual impeller, such as the mixing power [11] and [12] Each impeller dispersing air is limited by the maximum amount of air to be dispersed. Further increasing of the air flow rate causes flooding.

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“…Assuming that the integral scale is proportional to the vessel diameter, Nienow (1997) gives a correlation for mixing time with the third radical of the specific power input and geometrical parameters:…”

Section: Engineering Characteristics and Scale-up Issues 421 Power mentioning

confidence: 99%