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Gerhart Eigenberger - One of the best experts on this subject based on the ideXlab platform.
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applicability of the standard k e turbulence Model to the dynamic simulation of bubble columns part ii comparison of detailed experiments and flow simulations
Chemical Engineering Science, 1999Co-Authors: O Borchers, A Sokolichin, Claudia Busch, Gerhart EigenbergerAbstract:Gas–liquid bubble-flow was studied in a flat bubble column with rectangular cross-section. The bubble column was locally aerated through a frit sparger, located in the central part of the bottom plate. The experimental techniques used comprise photographic documentation of the bubble distribution as well as LDA measurements of the liquid velocity. The influence of the liquid level (aspect ratio) in the bubble column and of the gas through-put on the hydrodynamic behaviour of the column has been investigated. At aspect ratio of 1 steady state flow was observed with one circulation cell spread over the full width of the column. This differs from the flow behaviour in a uniformly aerated flat bubble column, reported by Chen, Jamialahmadi and Li (Chemical Engineering Research and Development 67 (1989) 203–207), who observed an essentially symmetric flow field with two stationary circulation cells. At aspect ratios of 2 and 3 the two-phase flow has a transient character with two staggered rows of vortices moving downwards in a periodic way. The long-time averaged liquid velocities obtained from the LDA measurements showed a symmetrical flow field, which is referred to in the literature as the “Gulf-stream” or “cooling-tower” pattern. The experimental results were compared with numerical simulations based upon the dynamic turbulent three-dimensional two-phase Euler–Euler Model presented in Part I (Sokolichin and Eigenberger, Chemical Engineering Science (1999) in press). Good qualitative and quantitative agreement was found for the steady state as well as for the transient case.
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gas liquid flow in bubble columns and loop reactors part i detailed Modelling and numerical simulation
Chemical Engineering Science, 1994Co-Authors: A Sokolichin, Gerhart EigenbergerAbstract:Abstract The state of the art of the Modelling of gas—liquid flow in bubble columns and loop reactors is critically reviewed. Recent results obtained with dynamic multidimensional two-fluid Models are compared with respective steady state simulations. It will be shown that no steady state solution for uniformly aerated bubble columns can be obtained above a certain gas velocity if a sufficiently fine space grid is used. A dynamic state is obtained instead where large and rising vortices are subsequently generated at the gas distributor. Only after a long time averaging is the well known flow structure with increased gas hold-up and liquid upflow in the column centre and reduced gas hold-up with downflow near the walls obtained. The above results are based upon a two-dimension Euler—Euler Model. The underlying assumptions and simplifications are discussed and the advantages and drawbacks of a corresponding Euler—Lagrangian formulation are considered. The Model is used in Part II of this contribution for a detailed comparison with the experimental results from a flat bubble column with various circulating flow patterns.
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gas liquid flow in bubble columns and loop reactors part ii comparison of detailed experiments and flow simulations
Chemical Engineering Science, 1994Co-Authors: S Becker, A Sokolichin, Gerhart EigenbergerAbstract:Gas-liquid bubble flow was studied in a flat bubble column with rectangular cross-section and essentially two-dimensional flow structure. Both a bubble column and an airlift loop reactor arrangement have been considered. The experimental techniques used comprise visual observation of the flow structure and photographic documentation of the bubble distribution as well as detailed measurements of the two-phase flow characteristics at distinct levels over the column width. The experimental results are compared with numerical simulations based upon the dynamic laminar two-dimensional two-phase Euler—Euler Model presented in Part I. The steady state as well as the transient behaviour was well reproduced in the simulations. Good quantitative agreement could be obtained if the value of the laminar viscosity used was increased by a factor 100 to account for the influence of turbulent viscosity. The standardk—ɛ Model results in a much higher increase in the viscosity which does not give satisfactory agreement in the range of the bubble flow regime considered.
A Sokolichin - One of the best experts on this subject based on the ideXlab platform.
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applicability of the standard k e turbulence Model to the dynamic simulation of bubble columns part ii comparison of detailed experiments and flow simulations
Chemical Engineering Science, 1999Co-Authors: O Borchers, A Sokolichin, Claudia Busch, Gerhart EigenbergerAbstract:Gas–liquid bubble-flow was studied in a flat bubble column with rectangular cross-section. The bubble column was locally aerated through a frit sparger, located in the central part of the bottom plate. The experimental techniques used comprise photographic documentation of the bubble distribution as well as LDA measurements of the liquid velocity. The influence of the liquid level (aspect ratio) in the bubble column and of the gas through-put on the hydrodynamic behaviour of the column has been investigated. At aspect ratio of 1 steady state flow was observed with one circulation cell spread over the full width of the column. This differs from the flow behaviour in a uniformly aerated flat bubble column, reported by Chen, Jamialahmadi and Li (Chemical Engineering Research and Development 67 (1989) 203–207), who observed an essentially symmetric flow field with two stationary circulation cells. At aspect ratios of 2 and 3 the two-phase flow has a transient character with two staggered rows of vortices moving downwards in a periodic way. The long-time averaged liquid velocities obtained from the LDA measurements showed a symmetrical flow field, which is referred to in the literature as the “Gulf-stream” or “cooling-tower” pattern. The experimental results were compared with numerical simulations based upon the dynamic turbulent three-dimensional two-phase Euler–Euler Model presented in Part I (Sokolichin and Eigenberger, Chemical Engineering Science (1999) in press). Good qualitative and quantitative agreement was found for the steady state as well as for the transient case.
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gas liquid flow in bubble columns and loop reactors part i detailed Modelling and numerical simulation
Chemical Engineering Science, 1994Co-Authors: A Sokolichin, Gerhart EigenbergerAbstract:Abstract The state of the art of the Modelling of gas—liquid flow in bubble columns and loop reactors is critically reviewed. Recent results obtained with dynamic multidimensional two-fluid Models are compared with respective steady state simulations. It will be shown that no steady state solution for uniformly aerated bubble columns can be obtained above a certain gas velocity if a sufficiently fine space grid is used. A dynamic state is obtained instead where large and rising vortices are subsequently generated at the gas distributor. Only after a long time averaging is the well known flow structure with increased gas hold-up and liquid upflow in the column centre and reduced gas hold-up with downflow near the walls obtained. The above results are based upon a two-dimension Euler—Euler Model. The underlying assumptions and simplifications are discussed and the advantages and drawbacks of a corresponding Euler—Lagrangian formulation are considered. The Model is used in Part II of this contribution for a detailed comparison with the experimental results from a flat bubble column with various circulating flow patterns.
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gas liquid flow in bubble columns and loop reactors part ii comparison of detailed experiments and flow simulations
Chemical Engineering Science, 1994Co-Authors: S Becker, A Sokolichin, Gerhart EigenbergerAbstract:Gas-liquid bubble flow was studied in a flat bubble column with rectangular cross-section and essentially two-dimensional flow structure. Both a bubble column and an airlift loop reactor arrangement have been considered. The experimental techniques used comprise visual observation of the flow structure and photographic documentation of the bubble distribution as well as detailed measurements of the two-phase flow characteristics at distinct levels over the column width. The experimental results are compared with numerical simulations based upon the dynamic laminar two-dimensional two-phase Euler—Euler Model presented in Part I. The steady state as well as the transient behaviour was well reproduced in the simulations. Good quantitative agreement could be obtained if the value of the laminar viscosity used was increased by a factor 100 to account for the influence of turbulent viscosity. The standardk—ɛ Model results in a much higher increase in the viscosity which does not give satisfactory agreement in the range of the bubble flow regime considered.
Rosa M. Quinta-ferreira - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional numerical simulation of pressure drop and liquid holdup for high-pressure trickle-bed reactor
Chemical Engineering Journal, 2008Co-Authors: Rodrigo J G Lopes, Rosa M. Quinta-ferreiraAbstract:Abstract This study aims to investigate the hydrodynamic behaviour of a trickle-bed reactor (TBR) at high pressure (30 bar) in terms of pressure drop and liquid holdup after the development of a multiphase Model by means of computational fluid dynamics (CFD) codes. Taking into account transport phenomena expressed as interphase coupling terms in the momentum transfer between the gas, liquid and solid phases, an Euler–Euler Model was developed resulting from the volume averaging of the continuity and momentum equations and solved for a 3D representation of the catalytic bed. The CFD calculations were validated with experimental data from the literature and different mesh sizes were evaluated for a grid-independent CFD solution of multiphase flow in the packed bed. During grid optimization, coarse and fine physical mesh domains were applied in the hydrodynamic prediction of trickle-bed reactor. After the grid adjustment in terms of number of cells, several spherical particle diameters were tested to study its effect on hydrodynamics and it was found that pressure drop is strongly influenced by the packing size. The Eulerian mutiphase Model was then used in the computation of pressure drop and liquid holdup and over a wide range for the calculated flow regime as a function of gas and liquid flow rates, the CFD theoretical predictions were in good agreement for both hydrodynamic parameters.
Milorad P. Dudukovic - One of the best experts on this subject based on the ideXlab platform.
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evaluation of large eddy simulation and Euler Euler cfd Models for solids flow dynamics in a stirred tank reactor
Aiche Journal, 2008Co-Authors: Debangshu Guha, Milorad P. Dudukovic, P A Ramachandran, J J DerksenAbstract:Mechanically agitated reactors find wide range of applications for solid suspension and mixing in the chemical, biochemical, and mineral processing industries. Understanding the solids dynamics in these reactors is necessary to improve the design and operation of such reactors. Computational fluid dynamic (CFD) Models are often useful in this regard, as it can provide significant insights into the flow and mixing of the phases involved. However, the Model predictions need extensive evaluation with experimental results before they can be confidently used for the scale-up and optimization of large scale reactors. Recently, Guha et al. carried out a systematic experimental investigation of the solids hydrodynamics in dense solid–liquid suspensions (2.5–19% solids loading w/w) in a stirred tank using the Computer Automated Radioactive Particle Tracking (CARPT) technique, which provided extensive information to efficiently assess the ability of the existing CFD Models in predicting the solids dynamics in slurry reactors. This work presents such an evaluation by comparing the averaged solids velocities, turbulent kinetic energy, and solids sojourn time distributions predicted by CFD Models with those obtained from the CARPT experiment for overall solids holdup of 1% (v/v) (2.5% w/w) at Reynolds number of 74,000. The Large Eddy Simulation (LES) and the Euler-Euler Model are the Models chosen for evaluation in the current study. 2008 American Institute of Chemical Engineers AIChE J, 54: 766–778, 2008
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numerical simulation of gas liquid dynamics in cylindrical bubble column reactors
Chemical Engineering Science, 1999Co-Authors: Jayanta Sanyal, Sergio Vasquez, Shantanu Roy, Milorad P. DudukovicAbstract:In this paper, we have attempted to validate a transient, two-dimensional axisymmetric simulation of a laboratory-scale cylindrical bubble column, run under bubbly flow and churn turbulent conditions. The experimental data was obtained via gamma-radiation based non-invasive flow monitoring methods, viz., computer automated radioactive particle tracking (CARPT) provided the data on liquid velocity and turbulence, and computed tomography (CT) determined the gas holdup profiles. The numerical simulation was done using the FLUENT software and compares the results from the algebraic slip mixture Model, and the two-fluid Euler–Euler Model. Reasonably, good quantitative agreement was obtained between the experimental data and simulations for the time-averaged gas holdup and axial liquid velocity profiles, as well as for the kinetic energy profiles. The favorable results suggest that the simple two-dimensional axisymmetric simulation can be used for reasonable engineering calculations of the overall flow pattern and gas holdup distributions.
Rodrigo J G Lopes - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional numerical simulation of pressure drop and liquid holdup for high-pressure trickle-bed reactor
Chemical Engineering Journal, 2008Co-Authors: Rodrigo J G Lopes, Rosa M. Quinta-ferreiraAbstract:Abstract This study aims to investigate the hydrodynamic behaviour of a trickle-bed reactor (TBR) at high pressure (30 bar) in terms of pressure drop and liquid holdup after the development of a multiphase Model by means of computational fluid dynamics (CFD) codes. Taking into account transport phenomena expressed as interphase coupling terms in the momentum transfer between the gas, liquid and solid phases, an Euler–Euler Model was developed resulting from the volume averaging of the continuity and momentum equations and solved for a 3D representation of the catalytic bed. The CFD calculations were validated with experimental data from the literature and different mesh sizes were evaluated for a grid-independent CFD solution of multiphase flow in the packed bed. During grid optimization, coarse and fine physical mesh domains were applied in the hydrodynamic prediction of trickle-bed reactor. After the grid adjustment in terms of number of cells, several spherical particle diameters were tested to study its effect on hydrodynamics and it was found that pressure drop is strongly influenced by the packing size. The Eulerian mutiphase Model was then used in the computation of pressure drop and liquid holdup and over a wide range for the calculated flow regime as a function of gas and liquid flow rates, the CFD theoretical predictions were in good agreement for both hydrodynamic parameters.