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

Sharaf, Safa; Zedníková, Mária; Růžička, Marek C.; Azzopardi, B.J.

doi:10.1016/j.cej.2015.11.106

Cited by 79 publications

(48 citation statements)

References 57 publications

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“…The transition flow regime is identified by the appearance of the "coalescence-induced" bubbles and is characterized by large flow macro-structures with large eddies and a widened bubble size distribution due to the onset of bubble coalescence. At high gas velocities, a fully heterogeneous flow regime is reached (Sharaf et al, 2015); it is associated with high coalescence and breakage rates and a wide variety of bubble sizes. The transitions between the different flow regimes depend on the operation mode, the design parameters of the bubble column and the properties of the gas/liquid phases.…”

Section: Bubble Column Fluid Dynamicsmentioning

confidence: 99%

“…Many authors consider only the first flow regime transition, without any reference to the second one, except for a limited number of studies (Nedeltchev, 2015;Nedeltchev and Shaikh, 2013;Sharaf et al, 2015). In the following, for the sake of clarity, we refer to "flow regime transition point" considering the first flow regime transition.…”

Section: Flow Regime Transitionmentioning

confidence: 99%

“…It is well known that the shape of the gas holdup curve (the relationship between the gas holdup and the gas superficial velocity) mainly depends on the gas sparger used and the diameter of its holes (Sharaf et al, 2015;Urseanu, 2000). "Coarse spargers" leads to monotonic gas holdup curves, whereas, when using "fine spargers", a peak in the gas holdup curve can appear (owing to the hindrance effects of the mono-dispersed BSDs).…”

Section: Influence Of Viscosity On the Flow Regime Transitionmentioning

confidence: 99%

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The dual effect of viscosity on bubble column hydrodynamics

Besagni

Inzoli

Guido

et al. 2017

Chemical Engineering Science

111

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A B S T R A C TSome authors, in the last decades, have observed the dual effect of viscosity on gas holdup and flow regime transition in small-diameter and small-scale bubble columns. This work concerns the experimental investigation of the dual effect of viscosity on gas holdup and flow regime transition as well as bubble size distributions in a large-diameter and large-scale bubble column. The bubble column is 5.3 m in height, has an inner diameter of 0.24 m, and can be operated with gas superficial velocities in the range of 0.004-0.20 m/s. Air was used as the dispersed phase, and various water-monoethylene glycol solutions were employed as the liquid phase. The water-monoethylene glycol solutions that were tested correspond to a viscosity between 0.9 mPa s and 7.97 mPa s, a density between 997.086 kg/m 3 and 1094.801 kg/m 3 , a surface tension between 0.0715 N/m and 0.0502 N/m, and log 10 (Mo) between −10.77 and −6.55 (where Mo is the Morton number). Gas holdup measurements were used to investigate the global fluid dynamics and the flow regime transition between the homogeneous flow regime and the transition flow regime. An image analysis method was used to investigate the bubble size distributions and shapes for different gas superficial velocities, for different solutions of watermonoethylene glycol. In addition, based on the experimental data from the image analysis, a correlation between the bubble equivalent diameter and the bubble aspect ratio was proposed. The dual effect of viscosity, previously verified in smaller bubble columns, was confirmed not only with respect to the gas holdup and flow regime transition, but also for the bubble size distributions. Low viscosities stabilize the homogeneous flow regime and increase the gas holdup, and are characterized by a larger number of small bubbles. Conversely, higher viscosities destabilize the homogeneous flow regime and decrease the gas holdup, and the bubble size distribution moves toward large bubbles. The experimental results suggest that the stabilization/destabilization of the homogeneous regime is related to the changes in the bubble size distributions and a simple approach, based on the lift force, was proposed to explain this relationship. Finally, the experimental results were compared to the dual effect of organic compounds and inorganic compounds: future studies should propose a comprehensive theory to explain all the dual effects observed.

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Section: Bubble Column Fluid Dynamicsmentioning

confidence: 99%

Section: Flow Regime Transitionmentioning

confidence: 99%

Section: Influence Of Viscosity On the Flow Regime Transitionmentioning

confidence: 99%

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The dual effect of viscosity on bubble column hydrodynamics

Besagni

Inzoli

Guido

et al. 2017

Chemical Engineering Science

111

View full text Add to dashboard Cite

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“…The gas distributor used in the present work was a perforated metal plate with wide spacing between large orifices (1.6 mm diameter). Regardless of the gas input into the bubble column, this distributor produces poly-dispersed bubble size distribution with presence of small and large bubbles [37,38] which is characteristic for pure heterogeneous regime. The monotonous dependence of gas hold-up on gas superficial velocity seen in Figure 3 is typical for a bubble column operated in pure heterogeneous regime [32,33].…”

Section: Description Of Hydrodynamicsmentioning

confidence: 99%

Measurement of Volumetric Mass Transfer Coefficient in Bubble Columns

et al. 2018

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Abstract:The paper presents a brief overview of experiments on volumetric mass transfer coefficient in bubble columns. The available experimental data published are often incomparable due to the different type of gas distributor and different operating conditions used by various authors. Moreover, the value of the coefficient obtained experimentally is very sensitive to the particular method and to the physical models used in its evaluation. It follows that the Dynamic Pressure Method (DPM) is able to provide physically correct values not only in lab-scale contactors but also in pilot-scale reactors. However, the method was not correctly proven in bubble columns. In present experiments, DPM was employed in a laboratory-scale bubble column with a coalescent phase and tested in the pure heterogeneous flow regime. The method was successfully validated by the measurements under two different conditions relevant to the mass transfer. First, the ideal pressure step was compared with the non-ideal pressure step. Second, the pure oxygen absorption was compared with the simultaneous oxygen-and-nitrogen absorption. The obtained results proved that DPM is suitable for measuring the mass transport in bubble columns and to provide reliable data of volumetric mass transfer coefficient.

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“…The former consists of a number of regularly spaced, small diameter holes drilled into the plate. A typical size for these orifices is 0.5 mm diameter [20], [21]. The porous type, which can be made of metal, plastic or glass, is produced by partially melting powders of these materials in a mould so that the particles fuse but leave passages in the sintered material through which fluids can pass [22]- [25].…”

Section: Relationships Characterising Bubble Behaviourmentioning

confidence: 99%

Characterisation of an analogue liquid for hydrodynamic studies of gas-ionic liquid flows

Azzopardi

Agunlejika

Zhao

et al. 2017

Chemical Engineering Journal

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Ionic liquids are liquid salts at low temperatures (normally less than 100°C). They are powerful solvents with very low vapour pressure. They have great potentials in many applications such as gas absorption and chemical synthesis. However, they are expensive. This limits extensive studies towards establishing phenomenological models. To address this limitation, an analogue liquid, with properties similar to an ionic liquid, has been identified which on the grounds of cost and safety appears to be suitable.In this paper, the hydrodynamic behaviour of an ionic liquid in a bubble column is compared with those of water and other liquids with similar physical properties. Average gas holdup, bubble coalescence, bubble size and specific interfacial area with different liquids are examined. Gas hold-up was determined by monitoring the change of conductivity between two flush mounted rings. The differences in bubble size and coalescence are revealed by analysing the stills taken from a high speed video camera. The dominant flow pattern in a small diameter column with ionic liquids or other fluids having similar viscosity is slug flow. The small bubbles in the liquid slugs make a smaller contribution to the specific interfacial area than Taylor bubbles. It is observed that Taylor bubbles can coalesce. The hydrodynamics of an ionic liquid in a bubble column can be estimated from that of a fluid with similar physical properties.

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

Cited by 79 publications

References 57 publications

The dual effect of viscosity on bubble column hydrodynamics

The dual effect of viscosity on bubble column hydrodynamics

Measurement of Volumetric Mass Transfer Coefficient in Bubble Columns

Characterisation of an analogue liquid for hydrodynamic studies of gas-ionic liquid flows

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