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Fluids
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Gas–Liquid Contactors: New Theoretical and Experimental Approaches for Their Better...
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Gas–Liquid Contactors: New Theoretical and Experimental Approaches for Their Better Understanding

A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 10335

Special Issue Editor

Prof. Dr. Stoyan Nedeltchev

E-Mail Website
Guest Editor
Institute of Chemical Engineering, Polish Academy of Sciences, 5 Baltycka St., 44-100 Gliwice, Poland
Interests: multiphase reactors; flow regime identification; sophisticated time series analysis; nonlinear chaos theory; information entropy; liquid mixing; gas-liquid mass transfer
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Gas–liquid contactors are one of the most important units in the chemical industry. In particular, bubble column reactors are widely used in absorption, oxidation, chlorination, oxichlorination, carboxylation, carbonylation, sulfonation, hydrogenation, polymerization, alkylation, esterification, etc. Most of these processes are accompanied by a slow chemical reaction. Fischer–Tropsch, methanol and dimethyl ether syntheses, and aerobic fermentation and biological wastewater treatment could also be implemented in effective gas–liquid contactors. Most of the gas–liquid contactors provide excellent mixing and mass and heat transfer characteristics.

The hydrodynamic behavior of the gas–liquid reactors is very complex, irrespective of their simple construction. When a chemical reaction takes place, several dead zones and many local inhomogeneities are formed. This leads to different local liquid mixing and volumetric liquid-phase mass transfer coefficients across the gas–liquid reactor. The radial profiles of both the gas holdups and liquid velocities are also different. These phenomena depend on the prevailing hydrodynamic regime. That is why new methods for reliable flow regime identification should be developed. In this Special Issue, all these important topics will be covered. Both new theoretical approaches and experimental techniques for better understanding of the hydrodynamic and mass transfer behavior of various gas–liquid contactors (bubble columns, agitated vessels, airlift reactors, etc.) will be presented.

Prof. Dr. Stoyan Nedeltchev
Guest Editor

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Keywords

  • hydrodynamics
  • mixing
  • gas–liquid mass transfer
  • bubble columns
  • agitated vessels
  • airlift reactors
  • new measurement techniques
  • reactor modelling

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Published Papers (3 papers)

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Research

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12 pages, 2935 KiB  
Article
Identification of Local Isotropic Turbulence Conditions in Various Bubble Columns Based on Several Reliable Parameters
by Stoyan Nedeltchev
Fluids 2023, 8(12), 314; https://doi.org/10.3390/fluids8120314 - 4 Dec 2023
Viewed by 1646
Abstract
Bubble columns (BCs) are widely used in the chemical industry. In many industrial applications, these important gas-liquid contactors operate in a churn-turbulent flow regime. In principle, it is essential to determine the operating conditions in every BC reactor, in which local isotropic turbulence [...] Read more.
Bubble columns (BCs) are widely used in the chemical industry. In many industrial applications, these important gas-liquid contactors operate in a churn-turbulent flow regime. In principle, it is essential to determine the operating conditions in every BC reactor, in which local isotropic turbulence is established. In this work, it was demonstrated that several different parameters (Kolmogorov entropy, correlation dimension and novel hybrid index) follow a monotonic decreasing trend. This finding could be explained by the constantly increasing coalesced bubble size, which brings more order into the gas-liquid system and thus any entropic or chaotic parameter should decrease with the increase in the superficial gas velocity Ug. The profiles of the new parameters in various gas-liquid systems were studied. They were extracted from different pressure signals (gauge or absolute). In this research, BCs of different diameter and equipped with different gas distributors were used. It was demonstrated that the studied parameters could be successfully correlated with the length scale of the micro eddies and thus the Ug range of applicability of the local isotropic turbulence theory under various operating conditions was indirectly determined. The overall gas holdup profiles were analyzed and, based on the exponent of the Ug value, it was found that in the aqueous solutions of alcohols studied, the conditions in the bubble bed (BB) are homogeneous, whereas in the air-tap water system aerated in different BCs, the conditions in the BB are heterogeneous. This result implies that the local isotropic turbulence conditions predominate mainly around the corresponding measurement positions. Full article
(This article belongs to the Special Issue Gas–Liquid Contactors: New Theoretical and Experimental Approaches for Their Better Understanding)
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10 pages, 1487 KiB  
Communication
Prediction of Small Bubble Holdups in Bubble Columns Operated with Various Organic Liquids at Both Ambient and Elevated Pressures and Temperatures
by Stoyan Nedeltchev
Fluids 2023, 8(6), 163; https://doi.org/10.3390/fluids8060163 - 24 May 2023
Viewed by 1160
Abstract
This article focuses on the prediction of the small bubble holdups (assuming the existence of two major bubble classes) in two bubble columns (0.289 m in ID and 0.102 m in ID), operated with organic liquids under various conditions (including high temperature and [...] Read more.
This article focuses on the prediction of the small bubble holdups (assuming the existence of two major bubble classes) in two bubble columns (0.289 m in ID and 0.102 m in ID), operated with organic liquids under various conditions (including high temperature and pressure). A new correction factor has been established in the existing model for the prediction of the gas holdups in the homogeneous regime. The correction parameter is a single function of the Eötvös number (gravitational forces to surface tension forces), which characterizes the bubble shape. In addition, the behavior of small bubble holdups in 1-butanol (selected as a frequently researched alcohol) aerated with nitrogen, in a smaller BC (0.102 m in ID), at various operating pressures, is presented and discussed. The ratio of small bubble holdup to overall gas holdup, as a function of superficial gas velocity and operating pressure, has been investigated. All small bubble holdups in this work have been measured by means of the dynamic gas disengagement technique. Full article
(This article belongs to the Special Issue Gas–Liquid Contactors: New Theoretical and Experimental Approaches for Their Better Understanding)
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Review

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41 pages, 1477 KiB  
Review
Computational Fluid Dynamics Modelling of Two-Phase Bubble Columns: A Comprehensive Review
by Giorgio Besagni, Nicolò Varallo and Riccardo Mereu
Fluids 2023, 8(3), 91; https://doi.org/10.3390/fluids8030091 - 3 Mar 2023
Cited by 12 | Viewed by 6699
Abstract
Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal [...] Read more.
Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal of developing a predictive tool that can track the complex dynamic phenomena occurring in these types of reactors. For this reason, we present a detailed literature review on the numerical simulation of two-phase bubble columns. First, after a brief introduction to bubble column technology and flow regimes, we discuss the state-of-the-art modelling approaches, presenting the models describing the momentum exchange between the phases (i.e., drag, lift, turbulent dispersion, wall lubrication, and virtual mass forces), Bubble-Induced Turbulence (BIT), and bubble coalescence and breakup, along with an overview of the Population Balance Model (PBM). Second, we present different numerical studies from the literature highlighting different model settings, performance levels, and limitations. In addition, we provide the errors between numerical predictions and experimental results concerning global (gas holdup) and local (void fraction and liquid velocity) flow properties. Finally, we outline the major issues to be solved in future studies. Full article
(This article belongs to the Special Issue Gas–Liquid Contactors: New Theoretical and Experimental Approaches for Their Better Understanding)
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