Surface Aeration Threshold in Agitated Vessels

Violent agitation of liquids in mixing vessels may result in the regime of surface aeration being attained when the bubbles formed at the liquid surface enter the impeller region. Analysis of data on surface aeration for different liquids in a set of geometrically similar agitated vessels is presented. Data on the just aerated state as observed visually in transparent liquids, and data for the efficient aeration as determined from the break on the power number curve are considered. A simple model is developed for correlation of the data which enables the threshold of aeration to be predicted from the value of the recirculation number Nc = Nd (ρ/σg)1/4. The possibility of interpreting various literature data for the aeration threshold and for the power input with use of Nc is demonstrated. Similar modelling rules hold also for the correlation of beginning of the efficient liquid-liquid dispersion.

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Free Level Effect on the Impeller Power Input in Baffled Tanks

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19951274 ◽

1995 ◽

Vol 60 (8) ◽

pp. 1274-1280 ◽

Cited By ~ 1

Author(s):

Kamil Wichterle

Keyword(s):

Reynolds Number ◽

Power Input ◽

Dimensionless Number ◽

Simple Correlation ◽

Mixture Density ◽

Surface Aeration ◽

Free Level ◽

High Reynolds ◽

Level Effect ◽

Turbine Impeller

Analysis of extended data on turbine impeller power input in geometrically similar agitated baffled tanks shows that the power number Po is a function of Reynolds number Po = Po*(Re) until the emergence of surface aeration. Though it is usually anticipated that Po* = const in high Reynolds number region, some, whatever weak, function should be taken into consideration in more detailed analysis of the power data even here. In practice, disturbances of level and gas captured in the impeller region play also a significant role, namely in smaller tanks at higher impeller speeds. Decrease of power input can be explained by decrease of gas-liquid mixture density, or in other words by increase of efficient gas holdup eE just in the impeller region. The value eE defined by the relation Po = Po*(Re)/(1 + eE) was determined from the available data. Like other effects of the surface aeration it depends mainly on the dimensionless number Nc = (We Fr)1/4. A simple correlation eE (Nc) is suggested as a correction factor for prediction of impeller power in presence of gas capture.

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Controlled Efficiency During Drilling With a High Intensity Beam

Volume 10: Micro- and Nano-Systems Engineering and Packaging ◽

10.1115/imece2013-63061 ◽

2013 ◽

Author(s):

J. H. Wu ◽

T. C. Chao ◽

P. S. Wei

Keyword(s):

High Intensity ◽

Liquid Surface ◽

Flow Behavior ◽

High Power Density ◽

Two Phase ◽

Thermal Physics ◽

Energy Beam ◽

Liquid Dispersion ◽

Manufacturing Technologies ◽

Critical Investigation

Drilling with a high intensity energy beam can be incapable if the keyhole induced is collapsed. In this work, we identify the conditions for the keyhole collapse during high power density beam drilling from fundamental principles of thermal physics. The approach adapted is to probe the supersonic flow behavior of the two-phase vapor-liquid dispersion in a vertical keyhole of varying cross-section, paying particular attention to the transition between the slug and annular flows. It shows that the keyhole collapse occur from entrainment around the keyhole wall resulting in a severely deformed wavy shape of the inner liquid surface of the keyhole. This work provides a critical investigation to reveal incapability of drilling encountered in materials processing, packaging and manufacturing technologies.

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Aeration of liquids in a vessel equipped with multistage impellers

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19852863 ◽

1985 ◽

Vol 50 (12) ◽

pp. 2863-2872 ◽

Cited By ~ 4

Author(s):

Václav Machoň ◽

Jiří Vlček

Keyword(s):

Input Data ◽

Power Input ◽

Experimental Results ◽

Simple Equation ◽

Mechanical Power ◽

System A ◽

Liquid Dispersion ◽

Liquid Depth ◽

Turbine Impeller ◽

Tank Diameter

The paper deals with the influence of the number of impellers and the mode of aeration on the mechanical power input in a stirred gas-liquid dispersion using two impellers on the same shaft. Gas has been supplied either under the lower impeller or under both impellers. The power input was measured in the water-air system. A six-blade turbine impeller of the Rushton type and/or impellers with six inclined blades (with downward or upward pumping effect) were used. Experimental results have been obtained for a single impeller in a tank where the depth of liquid was equal to the tank diameter, and for different combinations of two impellers located on a single shaft where the distance between the impellers was equal to the tank diameter and the liquid depth was twice this diameter. It has been found that the power input data for the two-impeller system of two turbines can be correlated adequately by a simple equation. An estimate was made of the amount of gas supplied below the lower impeller which was transported into the region of the upper impeller.

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A Method for Liquid Level Detection Under Complicated Boundary Conditions

Journal of Vibration and Acoustics ◽

10.1115/1.2203240 ◽

2006 ◽

Vol 128 (4) ◽

pp. 535-539 ◽

Cited By ~ 1

Author(s):

Frank May ◽

Jürg Dual

Keyword(s):

Simple Model ◽

Boundary Conditions ◽

Liquid Surface ◽

Experimental Results ◽

Liquid Level ◽

Longitudinal Vibrations ◽

Resonant Vibrations ◽

Vibrating System ◽

As If ◽

Liquid Level Detection

In this paper a method of liquid level detection by mechanical resonant vibrations is presented which is based on longitudinal vibrations of a steel capillary and is able to detect a liquid surface even if covered with foam, as well as if the fluid container is shut by a cap. The behavior of the vibrating system is calculated by a simple model and compared with experimental results.

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A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2017-0147 ◽

2018 ◽

Vol 16 (8) ◽

Cited By ~ 1

Author(s):

Li Liangchao ◽

Chen Ning ◽

Xiang Kefeng ◽

Xiang Beiping

Keyword(s):

Flow Pattern ◽

Bubble Size ◽

Power Input ◽

Gas Holdup ◽

Stirred Tank ◽

Balance Model ◽

Wall Region ◽

Gas Dispersion ◽

Loop Region ◽

Liquid Dispersion

Abstract The computational fluid dynamics (CFD) combined with a population balance model (PBM) was applied to simulate gas-liquid dispersion in a stirred tank with low and high gas loadings. The model predictions were validated by using the data in the literature. The simulation results show that the flow patterns and gas dispersion characteristics are very different in the stirred tank for low and high gas loadings. A typical two-loop flow pattern forms as that in single-phase stirred tank for low gas loadings, while a triple-loop flow pattern, with two recirculation loops above and one below the impeller is found in the tank for high gas loadings. Shaft power input of impeller agitation plays a major role for gas dispersion with low gas loadings. For high gas loadings, the potential energy due to gas sparging has significant effect on gas dispersion and can not be neglected. Compared to low gas loading, high gas loading causes average gas holdup increased in the stirred tank, while relative local gas holdup in the lower circulation-loop region and near-wall region reduced. The ability of impeller agitation for gas dispersion reduces with high gas loadings, and mean bubble size becomes larger and the volume-averaged bubble size distribution is wider.

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Studies on oxygen mass transfer in stirred bioreactors 2: Suspensions of bacteria, yeasts and fungis

Hemijska industrija ◽

10.2298/hemind0306276g ◽

2003 ◽

Vol 57 (6) ◽

pp. 276-287 ◽

Cited By ~ 5

Author(s):

Anca-Irina Galaction ◽

Corneliu Oniscu ◽

Dan Cascaval

Keyword(s):

Mass Transfer ◽

Mass Transfer Rate ◽

Power Input ◽

Specific Power ◽

Oxygen Mass Transfer ◽

Stirred Bioreactor ◽

Operating Variables ◽

Surface Aeration ◽

Velocity Surface ◽

Specific Power Input

The aim of these experiments is to study the oxygen mass transfer rate by means of the mass transfer coefficient, for a stirred bioreactor and different fermentation broths, using a large domain of operating variables. For quantifying the effects of the considered factors (concentration and morphology of the biomass, specific power input, superficial air velocity surface aeration) on k\a, the experiments were carried out for non-respirating biomass suspensions of Propionibacterium shermanii Saccharomyces cerevisiae and Penicillium chrysogenum, mycelial aggregates (pellets) and free mycelia morphological structures.

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Power input of aerated agitator system of high-speed fermenter

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19872181 ◽

1987 ◽

Vol 52 (9) ◽

pp. 2181-2187 ◽

Cited By ~ 10

Author(s):

Pavel Seichter

Keyword(s):

Simple Model ◽

High Speed ◽

Power Input ◽

Model Idea

A correlation complying a simple model idea about function of an agitator in aerated high hold-up system has been found on basis of power input measurement of four fermenter agitators.

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