Special Issue "Bubble Column Fluid Dynamics"
A special issue of ChemEngineering (ISSN 2305-7084).
Deadline for manuscript submissions: 28 February 2018
Dr. Thomas Ziegenhein
Helmholtz-Zentrum Dresden-Rossendorf e. V. Institute of Fluid Dynamics, 01314 Dresden, Germany
Interests: bubbly flow; multi-phase turbulence; PIV; PTV; CFD
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
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- bubble columns
- flow regime
- Gas holdup
- bubble size and shape
The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.
Title: Gas-liquid mass transfer measurements of rising toroidal bubbles in quiescent liquids
Authors: Nicolas Dietrich a,b,c, Mélanie Jimenez a,b,c and Gilles Hébrard a,b,c
a Université de Toulouse, INSA, LISBP, 135 Av. de Rangueil, F-31077 Toulouse, France
b INRA UMR792, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France
c CNRS UMR 5504, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France
Abstract：Multiphase flows and especially gas-liquid systems play an important role in many natural and industrial processes such as combustion, petroleum refining, chemical engineering and water treatments. Their efficiency is directly linked to their design and requires a profound understanding of mass transfer phenomena. This transfer depends on the bubble shape and has been widely studied in past decades. Impressive developments in the visualization of ﬂuid structure, detailed ﬂow-field measurements, and sophisticated numerical simulations have led to significant progress in the understanding of complex diphasic ﬂows in recent years, however, difficulties are still encountered. While a lot of studies have focused on the visualization of mass transfer by fluorescence quenching by oxygen called PLIFI technique (Planar Laser Induced Fluorescence with Inhibition) around spherical bubble (Francois et al. 2011) and ellipsoidal bubbles (Stohr et al. 2009 & Jimenez et al. 2013) nothing have been performed about toroidal bubbles. This kind of gas structure has been observed by Walters & Davidson (1963) when an important mass of gas in water is injected in a small time producing a rising ring bubble. In this paper, we investigated experimentally the ascension of ring air bubbles in a quiescent Newtonian liquid. In parallel we carry out mass transfer visualization on two distinct approaches, PLIFI (fluorescence quenching) and an oxygen-sensitive dye colorimetric technique (Fig. 1.a. and b.). Classical probe analyses for kL measurements have been performed in order to compare the quantification of mass transfer and also Particle Image Velocimetry (PIV, fig 1.c) measurements to characterize the hydrodynamics structure.
Title: On the Design of Bubble Columns Equipped with Fine Pore Sparger: Effect of Gas Properties
Author: Aikaterini A. Mouza
Affiliation: Laboratory of Chemical Process and Plant Design, Department of Chemical Engineering, Aristotle University of Thessaloniki, University Box 455, GR 54124 Thessaloniki, Greece
Abstract: The work, that has been conducted in our Lab during the last decade and concerns bubble columns equipped with fine pore metal spargers, has led to the development of design equations that can predict with reasonable accuracy (i.e. better than ±15%) the transition point from homogenous to heterogeneous regime as well as the gas holdup and the mean Sauter diameter at the homogenous regime. The validity of the proposed correlations was checked with data obtained using different geometrical config-urations and various Newtonian and non-Newtonian liquids as well as the addition of surfactants. How-ever, in all the experiments the gas phase was atmospheric air. In the present work the effect of gas phase properties is investigated by conducting experiments employing various gases (i.e., air, CO2, He) that cover a wide range of physical property values. A fast video technique is employed for visual observa-tions and, combined with image processing, is used for collecting data regarding gas holdup and bubble size distribution. The initial experiments revealed that only the 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. It is found that the new correlations can predict the afore-mentioned quantities with ±15% accuracy. More experimental and numerical work is currently in progress in an effort to also investigate the wall effects on the operation of small bubble columns (e.g. dC < 10 cm) when various fluids are employed as liquid and gas phases.
Title: High Amplitude Vibration on Enhancement of Mass Transfer and Phase Interfacial Area in Bubble Column
Authors: Shahrouz Mohagheghian 1, Adam L. Still 2, Brian R. Elbing 1 and Afshin J. Ghajar 1
1 Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, Oklahoma, USA
2 Engineering Science Center, Sandia National Laboratories, Albuquerque, New Mexico, USA
Abstract: Bubble Columns are in touch with numerous chemical, petroleum, and bio-systems processing applications. Vertical vibration is known to account for bubble clustering and retardation in gas-liquid system. In a contact reactor (e.g. bubble column) vibration increases the mass transfer ratio by increasing the residence time and phase interfacial area through introducing kinetic buoyancy force. Despite previous works, yet the physical mechanisms which governs a multiphase system under kinetic buoyancy forces is not fully understood. Previous works explored the effect of vibration frequency (10 < f < 120 Hz) while, very little effort has been made to understand the effect of (high) amplitude on mass transfer intensification. Therefore, a new experimental set up was designed, built, verified by comparison to previous research, and used to collect mass transfer, void fraction, and bubble size data at high amplitude (2.5 mm < A < 9.5 mm) over a frequency range of 7.5–22.5 Hz. Results of this work indicates an optimum amplitude independent of vibration frequency for mass transfer enhancements. Vibration frequency exhibits local maxima’s in both mass transfer and void fraction. In addition, this work suggests a strong correlation between mass transfer and kinetic buoyancy.
Title: Two-phase bubble column fluid dynamics: a comprehensive review
Authors: Giorgio Besagni 1,*, Fabio Inzoli 1 and Thomas Ziegenhein 2
Abstract: Two-phase bubble columns are equipment used for bringing a dispersed phase into contact with a continuous phase. Despite the simple column arrangement, bubble columns are characterized by extremely complex fluid dynamic interaction between the phases. This paper presents a literature review on bubble column fluid dynamics at the different scales and it deeply analyzes the flow regimes, the flow regime transitions, the local and the global fluid dynamics parameters. First, we discussed about the flow regimes, the flow regime transitions, and the local and the global fluid dynamics parameters. We also discussed how the operating parameters (i.e., the pressure, the temperature, and the gas and the 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., sparger design, column diameter and aspect ratio) influence the flow regime transitions and the fluid dynamics parameters. Secondly, we presented the experimental techniques to study the global and the local fluid dynamic properties. Finally, we presented the modeling approaches to study the global and the local bubble column fluid dynamics, and we outlined the major issues to be solved in the future studies.
Keywords: Bubble column; flow regimes; gas holdup; bubble size distribution; multi-scale; modeling
Title: The bubble shape in contaminated bubble columns: Results for different NaCl concentrations in water
Authors: Thomas Ziegenhein 1,2,*, Dirk Lucas 1, Giorgio Besagni 3 and Fabio Inzoli 3
1 Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany
2 Arizona State University, P.O. Box 876106, Tempe, AZ 85287, U.S.A.
3 Politecnico di Milano, Department of Energy, Via Lambruschini 4a, 20156, Milano
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 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 in which extend the NaCl concentration affect 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 execute independent from each other and were evaluated with different methods. All experiments show that the bubble shape is not distinctly affected in the evaluated concertation range from 0 – 1 M NaCl, which is in contrast to a previous study on single bubbles. Therefore, the effect of NaCl on the hydrodynamics of bubbly flow is not induced by the bubble shape.