New Evidence for the Mixing Length Concept in a Narrow Bubble Column Operated in the Transition Regime

Nedeltchev, Stoyan; Donath, Thomas; Rabha, Swapna; Hampel, Uwe; Schubert, Markus

doi:10.1252/jcej.13we362

Cited by 10 publications

(4 citation statements)

References 21 publications

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“…Nedeltchev et al [ 24 ] identified the two transition velocities U trans (0.022 and 0.112 m s −1 ) in the narrow column on the basis of the local minima in both the Kolmogorov entropy and the N v max (step 0.25) profiles. The photographs in Fig.…”

Section: Resultsmentioning

confidence: 99%

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A New Statistical Parameter for Identifying the Main Transition Velocities in Bubble Columns*

et al. 2015

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The identification of the main flow regime boundaries in bubble columns is essential since the degrees of mixing and mass and heat transfer vary with the flow regime. In this work, a new statistical parameter was extracted from the time series of the cross-sectional averaged gas holdup. The measurements were performed in bubble columns by means of conductivity wire-mesh sensors at very high sampling frequency. The columns were operated with an air/deionized water system under ambient conditions. As a flow regime indicator, a new dimensionless statistical parameter called “relative maximum number of visits in a region” was introduced. This new parameter is a function of the difference between the maximum numbers of visits in a region, calculated from two different division schemes of the signal range.

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Section: Resultsmentioning

confidence: 99%

“…Nedeltchev et al [ 24 ] found that, when the range of the gas holdup time series signal was divided into different regions (with progressively increasing heights proportional to the division step of 0.25, i.e. 1 × 0.25, 2 × 0.25, 3 × 0.25, 4 × 0.25, etc., shown in Fig.…”

Section: The Essence Of the New Methodsmentioning

confidence: 99%

A New Statistical Parameter for Identifying the Main Transition Velocities in Bubble Columns*

et al. 2015

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“…Both transitions were identified clearly by the well-pronounced two local minima. It is noteworthy that Nedeltchev et al [9] (based on the gas holdup fluctuations averaged over the whole cross-section) also reached the conclusion that the second transition velocity U trans occurred at U G =0.112 m/s. It was found that the IE values at the radial position P2 were not capable of identifying clearly the two U trans values (the figure is not shown).…”

Section: Experimental Setup and Measurement Techniquementioning

confidence: 92%

“…A new approach for flow regime identification based on the gas holdups averaged over the whole cross-section was reported in Nedeltchev et al [9]. However, the matrix data allows to also study the effect of the radial position on the transition velocities.…”

Section: Experimental Setup and Measurement Techniquementioning

confidence: 99%

Experimental study on the radial distribution of the main transition velocities in bubble columns

Nedeltchev¹,

Hampel²,

Schubert³

2015

Computational Methods in Multiphase Flow VIII

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The effect of the radial position on the main transition velocities in bubble columns has not been reported in the literature hitherto. In this paper, the information entropies IE were extracted in a new way from local gas holdup fluctuations measured by a wire-mesh sensor at different radial positions in both small (0.15 m in ID) and large (0.4 m in ID) bubble columns. On the basis of well-defined local minima in the IE profiles, the transition velocities U trans at the different radial positions were identified successfully. It was found that in the small column the first transition velocity U trans,1 (corresponding to the end of the gas maldistribution regime) was somewhat lower in the center of the column as compared to the wall. In the large column, the U trans,1 value in the center was somewhat higher than the one at the wall. The second transition velocity U trans,2 (corresponding to the onset of the churn-turbulent regime) in the small column was slightly higher at the core of the column. In the large column, the U trans,2 value was changing constantly from U G =0.089 m/s to 0.101 m/s and vice versa. The IE results showed that only at the fifth radial position in the small column and at the third and fourth radial positions in the large column there was a division of the transition regime into first and second transition sub-regimes.

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Global and local hydrodynamics of bubble columns – Effect of gas distributor

Sharaf

Zedníková

Růžička

et al. 2016

Chemical Engineering Journal

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New Evidence for the Mixing Length Concept in a Narrow Bubble Column Operated in the Transition Regime

Cited by 10 publications

References 21 publications

A New Statistical Parameter for Identifying the Main Transition Velocities in Bubble Columns*

A New Statistical Parameter for Identifying the Main Transition Velocities in Bubble Columns*

Experimental study on the radial distribution of the main transition velocities in bubble columns

Global and local hydrodynamics of bubble columns – Effect of gas distributor

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