Special Issue "Bubble Column Fluid Dynamics"

A special issue of ChemEngineering (ISSN 2305-7084).

Deadline for manuscript submissions: closed (20 September 2018).

Special Issue Editors

Guest Editor
Dr. Giorgio Besagni Website E-Mail
Politecnico di Milano, Department of Energy, Via Lambruschini 4a, 20156 Milano, Italy
Interests: innovative renewable energy-based technologies; CFD and lumped parameter modelling of energy system components; modelling of refrigeration systems; experimental and numerical investigations of multiphase flows; energy poverty
Guest Editor
Dr. Thomas Ziegenhein E-Mail
Helmholtz-Zentrum Dresden-Rossendorf e. V. Institute of Fluid Dynamics, 01314 Dresden, Germany
Interests: bubbly flow; multi-phase turbulence; PIV; PTV; CFD

Special Issue Information

Dear Colleagues,

Bubble columns are widely used multiphase reactors where a gas phase is dispersed into a continuous phase. The simplest configuration consists in a vertical cylinder, in which the gas enters through a gas sparger located at the bottom, and the liquid phase is supplied in the batch mode or it may be led in either co-currently or counter-currently to the upward gas stream. Despite the simple column arrangement, bubble columns are characterized by extremely complex fluid dynamic interactions between the phases. For these reasons, their correct design, operation and scale-up rely on the knowledge of the fluid dynamics at “bubble-scale” and at the “reactor-scale”.

An understanding of the fluid dynamics and the transport phenomena in bubble columns (in the homogeneous and heterogeneous flow regimes) is of fundamental importance to support the design and scale-up methods. In this respect, multiphase Computational Fluid-Dynamics (CFD) simulations are particularly useful to study the fluid dynamics in large-scale reactors. Reliable predictions of the homogeneous flow regime with this approach are, however, limited up to now. One important drawback concern the closure models for the interphase forces, turbulence and coalescence and break-up. One difficulty for the model development and validation results from the fact that we still have a lack of knowledge on local phenomena which determine the two-phase flow characteristics and which should be considered in the closure models. To this end, experimental data with high resolution in space and time are requested.

The Special Issue aims to collect contributions of the state-of-the-art on the multi-scale fluid dynamics of bubble columns. The main focus of the volume is on bubble column fluid dynamics without and with mass transfer by using theoretical, experimental, and numerical modeling approaches. Contributions concerning (a) bubble size and shapes and (b) flow regime transition prediction and modeling are strongly encouraged.

Dr. Giorgio Besagni
Dr. Thomas Ziegenhein
Guest Editors

Manuscript Submission Information

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Keywords

  • multi-phase
  • bubble columns
  • flow regime
  • experimental
  • CFD
  • Gas holdup
  • bubble size and shape
  • multi-scale

Published Papers (8 papers)

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Research

Open AccessArticle
Euler–Lagrange Modeling of Bubbles Formation in Supersaturated Water
ChemEngineering 2018, 2(3), 39; https://doi.org/10.3390/chemengineering2030039 - 24 Aug 2018
Abstract
Phase transition, and more specifically bubble formation, plays an important role in many industrial applications, where bubbles are formed as a consequence of reaction such as in electrolytic processes or fermentation. Predictive tools, such as numerical models, are thus required to study, design [...] Read more.
Phase transition, and more specifically bubble formation, plays an important role in many industrial applications, where bubbles are formed as a consequence of reaction such as in electrolytic processes or fermentation. Predictive tools, such as numerical models, are thus required to study, design or optimize these processes. This paper aims at providing a meso-scale modelling description of gas–liquid bubbly flows including heterogeneous bubble nucleation using a Discrete Bubble Model (DBM), which tracks each bubble individually and which has been extended to include phase transition. The model is able to initialize gas pockets (as spherical bubbles) representing randomly generated conical nucleation sites, which can host, grow and detach a bubble. To demonstrate its capabilities, the model was used to study the formation of bubbles on a surface as a result of supersaturation. A higher supersaturation results in a faster rate of nucleation, which means more bubbles in the column. A clear depletion effect could be observed during the initial growth of the bubbles, due to insufficient mixing. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
Measurement of Volumetric Mass Transfer Coefficient in Bubble Columns
ChemEngineering 2018, 2(2), 19; https://doi.org/10.3390/chemengineering2020019 - 01 May 2018
Cited by 2
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
The Bubble Shape in Contaminated Bubbly Flows: Results for Different NaCl Concentrations in Purified Water
ChemEngineering 2018, 2(2), 18; https://doi.org/10.3390/chemengineering2020018 - 24 Apr 2018
Cited by 1
Abstract
The bubble shape influences the transfer of momentum and heat/mass between the bubble and the surrounding fluid as well as the flow field around the bubble. The shape is determined by the interaction of the fluid field in the bubble, the physics on [...] Read more.
The bubble shape influences the transfer of momentum and heat/mass between the bubble and the surrounding fluid as well as the flow field around the bubble. The shape is determined by the interaction of the fluid field in the bubble, the physics on the surface, and the surrounding flow field. It is well known that contaminations can disturb the surface physics so that the bubble shape can be influenced. Indeed, an influence of sodium chloride (NaCl) on the hydrodynamics of bubbly flows was shown for air/water systems in previous studies. The aim of the present work is to investigate if, and to what extent, the NaCl concentration affects the bubble shape in bubble columns. For this purpose, several experiments at the Helmholtz-Zentrum Dresden-Rossendorf and at the pilot-scale bubble column at the Politecnico di Milano are evaluated. The experiments were executed independently from each other and were evaluated with different methods. All experiments show that the bubble shape is not distinctly affected in the examined concentration range from 0 to 1 M NaCl, which is in contrast to a previous study on single bubbles. Therefore, the effect of NaCl on the hydrodynamics of bubbly flows is not induced by the bubble shape. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
Study of Bubble Size, Void Fraction, and Mass Transport in a Bubble Column under High Amplitude Vibration
ChemEngineering 2018, 2(2), 16; https://doi.org/10.3390/chemengineering2020016 - 17 Apr 2018
Cited by 1
Abstract
Vertical vibration is known to cause bubble breakup, clustering and retardation in gas-liquid systems. In a bubble column, vibration increases the mass transfer ratio by increasing the residence time and phase interfacial area through introducing kinetic buoyancy force (Bjerknes effect) and bubble breakup. [...] Read more.
Vertical vibration is known to cause bubble breakup, clustering and retardation in gas-liquid systems. In a bubble column, vibration increases the mass transfer ratio by increasing the residence time and phase interfacial area through introducing kinetic buoyancy force (Bjerknes effect) and bubble breakup. Previous studies have explored the effect of vibration frequency (f), but minimal effort has focused on the effect of amplitude (A) on mass transfer intensification. Thus, the current work experimentally examines bubble size, void fraction, and mass transfer in a bubble column under relatively high amplitude vibration (1.5 mm < A <9.5 mm) over a frequency range of 7.5–22.5 Hz. Results of the present work were compared with past studies. The maximum stable bubble size under vibration was scaled using Hinze theory for breakage. Results of this work indicate that vibration frequency exhibits local maxima in both mass transfer and void fraction. Moreover, an optimum amplitude that is independent of vibration frequency was found for mass transfer enhancements. Finally, this work suggests physics-based models to predict void fraction and mass transfer in a vibrating bubble column. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
Two-Phase Bubble Columns: A Comprehensive Review
ChemEngineering 2018, 2(2), 13; https://doi.org/10.3390/chemengineering2020013 - 27 Mar 2018
Cited by 14
Abstract
We present a comprehensive literature review on the two-phase bubble column; in this review we deeply analyze the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer phenomena. First, we discuss the flow regimes, the [...] Read more.
We present a comprehensive literature review on the two-phase bubble column; in this review we deeply analyze the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer phenomena. First, we discuss the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer. We also discuss how the operating parameters (i.e., pressure, temperature, and gas and liquid flow rates), the operating modes (i.e., the co-current, the counter-current and the batch modes), the liquid and gas phase properties, and the design parameters (i.e., gas sparger design, column diameter and aspect ratio) influence the flow regime transitions and the fluid dynamics parameters. Secondly, we present the experimental techniques for studying the global and local fluid dynamic properties. Finally, we present the modeling approaches to study the global and local bubble column fluid dynamics, and we outline the major issues to be solved in future studies. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
Hydrodynamics of Bubble Columns: Turbulence and Population Balance Model
ChemEngineering 2018, 2(1), 12; https://doi.org/10.3390/chemengineering2010012 - 19 Mar 2018
Cited by 1
Abstract
This paper presents an in-depth numerical analysis on the hydrodynamics of a bubble column. As in previous works on the subject, the focus here is on three important parameters characterizing the flow: interfacial forces, turbulence and inlet superficial Gas Velocity (UG). The bubble [...] Read more.
This paper presents an in-depth numerical analysis on the hydrodynamics of a bubble column. As in previous works on the subject, the focus here is on three important parameters characterizing the flow: interfacial forces, turbulence and inlet superficial Gas Velocity (UG). The bubble size distribution is taken into account by the use of the Quadrature Method of Moments (QMOM) model in a two-phase Euler-Euler approach using the open-source Computational Fluid Dynamics (CFD) code OpenFOAM (Open Field Operation and Manipulation). The interfacial forces accounted for in all the simulations presented here are drag, lift and virtual mass. For the turbulence analysis in the water phase, three versions of the Reynolds Averaged Navier-Stokes (RANS) k-ε turbulence model are examined: namely, the standard, modified and mixture variants. The lift force proves to be of major importance for a trustworthy prediction of the gas volume fraction profiles for all the (superficial) gas velocities tested. Concerning the turbulence, the mixture k-ε model is seen to provide higher values of the turbulent kinetic energy dissipation rate in comparison to the other models, and this clearly affects the prediction of the gas volume fraction in the bulk region, and the bubble-size distribution. In general, the modified k-ε model proves to be a good compromise between modeling simplicity and accuracy in the study of bubble columns of the kind undertaken here. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
The Effects of the Properties of Gases on the Design of Bubble Columns Equipped with a Fine Pore Sparger
ChemEngineering 2018, 2(1), 11; https://doi.org/10.3390/chemengineering2010011 - 12 Mar 2018
Cited by 1
Abstract
This work concerns the performance of bubble columns equipped with porous sparger and investigates the effect of gas phase properties by conducting experiments with various gases (i.e., air, CO2, He) that cover a wide range of physical property values. The purpose [...] Read more.
This work concerns the performance of bubble columns equipped with porous sparger and investigates the effect of gas phase properties by conducting experiments with various gases (i.e., air, CO2, He) that cover a wide range of physical property values. The purpose is to investigate the validity of the design equations, which were proposed in our previous work and can predict with reasonable accuracy the transition point from homogeneous to heterogeneous regime as well as the gas holdup and the mean Sauter diameter at the homogeneous regime. Although, the correlations were checked with data obtained using different geometrical configurations and several Newtonian and non-Newtonian liquids, as well as the addition of surfactants, the gas phase was always atmospheric air. The new experiments revealed that only the use of low-density gas (He) has a measurable effect on bubble column performance. More precisely, when the low-density gas (He) is employed, the transition point shifts to higher gas flow rates and the gas holdup decreases, a fact attributed to the lower momentum force exerted by the gas. In view of the new data, the proposed correlations have been slightly modified to include the effect of gas phase properties and it is found that they can predict the aforementioned quantities with an accuracy of ±15%. It has been also proved that computational fluid dynamics (CFD) simulations are an accurate means for assessing the flow characteristics inside a bubble column. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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Open AccessArticle
Modelling of Bubbly Flow Using CFD-PBM Solver in OpenFOAM: Study of Local Population Balance Models and Extended Quadrature Method of Moments Applications
ChemEngineering 2018, 2(1), 8; https://doi.org/10.3390/chemengineering2010008 - 27 Feb 2018
Cited by 1
Abstract
In order to optimize and design new bubbly flow reactors, it is necessary to predict the bubble behavior and properties with respect to the time and location. In gas-liquid flows, it is easily observed that the bubble sizes may vary widely. The bubble [...] Read more.
In order to optimize and design new bubbly flow reactors, it is necessary to predict the bubble behavior and properties with respect to the time and location. In gas-liquid flows, it is easily observed that the bubble sizes may vary widely. The bubble size distribution is relatively sharply defined, and bubble rises are uniform in homogeneous flow; however bubbles aggregate, and large bubbles are formed rapidly in heterogeneous flow. To assist in the analysis of these systems, the volume, size and other properties of dispersed bubbles can be described mathematically by distribution functions. Therefore, a mathematical modeling tool called the Population Balance Model (PBM) is required to predict the distribution functions of the bubble motion and the variation of their properties. In the present paper, two rectangular bubble columns and a water electrolysis reactor are modeled using the open-source Computational Fluid Dynamic (CFD) package OpenFOAM. Furthermore, the Method of Classes (CM) and Quadrature-based Moments Method (QBMM) are described, implemented and compared using the developed CFD-PBM solver. These PBM tools are applied in two bubbly flow cases: bubble columns (using a Eulerian-Eulerian two-phase approach to predict the flow) and a water electrolysis reactor (using a single-phase approach to predict the flow). The numerical results are compared with measured data available in the scientific literature. It is observed that the Extended Quadrature Method of Moments (EQMOM) leads to a slight improvement in the prediction of experimental measurements and provides a continuous reconstruction of the Number Density Function (NDF), which is helpful in the modeling of gas evolution electrodes in the water electrolysis reactor. Full article
(This article belongs to the Special Issue Bubble Column Fluid Dynamics)
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