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Euler-euler modeling of flow, mass transfer, and chemical reaction in a bubble column / Dongsheng Zhang in Industrial & engineering chemistry research, Vol. 48 N°1 (Janvier 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - p. 47-57 Titre : Euler-euler modeling of flow, mass transfer, and chemical reaction in a bubble column Type de document : texte imprimé Auteurs : Dongsheng Zhang, Editeur scientifique ; Niels G. Deen, Editeur scientifique ; J. A. M. Kuipers, Editeur scientifique Année de publication : 2009 Article en page(s) : p. 47-57 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Chemical  Reaction  Physical  and  chemical  absorption  CO2 Résumé : Physical and chemical absorption of pure CO2 bubbles in water and an aqueous sodium hydroxide (NaOH) solution has been studied in a square cross-sectioned bubble column using the commercial software package CFX-4.4. The subgrid-scale turbulence model of Vreman [Phys. Fluids 2004, 16, 3670−3681] was employed to evaluate the shear-induced turbulent viscosity in the liquid phase. An “opening” boundary condition was applied at the outlet, whereas the previously studied interfacial coefficients were used in the simulations. Full coupling of fluid flow, mass transfer, and chemical reaction is achieved through the incorporation of a bubble number density equation. The capability of the bubble number density model to predict the bubble size is investigated first. Subsequently, physical absorption of pure CO2 in water and chemisorption of pure CO2 bubbles in an aqueous NaOH solution are numerically studied. It was verified for a test case without absorption that the specified bubble size can be reproduced with the aid of a bubble number density equation. For the physical absorption of CO2 in water, it is found that generally the size of the bubbles in the core of the bubble plume is larger than that of the bubbles trapped in the downflow along the wall. In this test case, the bubble size ranges from 3 to 4 mm. As time proceeds, the differences in bubble size become smaller in both the horizontal and vertical directions. When pure CO2 is absorbed into an aqueous NaOH solution with an initial pH value of 12, the bubble size does not change very much with time. In this case, the bubble size ranges from 2.7 to 4 mm because the mass-transfer enhancement factor is on the order of unity, as a result of the relatively low pH. The pH history resulting from the numerical model is compared to that obtained from a simple macroscopic model. It is found that numerical results obtained from the case in which the bubble size is solved agree well with the simple model. The observed differences between the simple model and the simulated results obtained with constant bubble size are due to the lack of coupling of mass transfer and fluid flow. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800233y [article] Euler-euler modeling of flow, mass transfer, and chemical reaction in a bubble column [texte imprimé] / Dongsheng Zhang, Editeur scientifique ; Niels G. Deen, Editeur scientifique ; J. A. M. Kuipers, Editeur scientifique . - 2009 . - p. 47-57. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - p. 47-57 Mots-clés : Chemical  Reaction  Physical  and  chemical  absorption  CO2 Résumé : Physical and chemical absorption of pure CO2 bubbles in water and an aqueous sodium hydroxide (NaOH) solution has been studied in a square cross-sectioned bubble column using the commercial software package CFX-4.4. The subgrid-scale turbulence model of Vreman [Phys. Fluids 2004, 16, 3670−3681] was employed to evaluate the shear-induced turbulent viscosity in the liquid phase. An “opening” boundary condition was applied at the outlet, whereas the previously studied interfacial coefficients were used in the simulations. Full coupling of fluid flow, mass transfer, and chemical reaction is achieved through the incorporation of a bubble number density equation. The capability of the bubble number density model to predict the bubble size is investigated first. Subsequently, physical absorption of pure CO2 in water and chemisorption of pure CO2 bubbles in an aqueous NaOH solution are numerically studied. It was verified for a test case without absorption that the specified bubble size can be reproduced with the aid of a bubble number density equation. For the physical absorption of CO2 in water, it is found that generally the size of the bubbles in the core of the bubble plume is larger than that of the bubbles trapped in the downflow along the wall. In this test case, the bubble size ranges from 3 to 4 mm. As time proceeds, the differences in bubble size become smaller in both the horizontal and vertical directions. When pure CO2 is absorbed into an aqueous NaOH solution with an initial pH value of 12, the bubble size does not change very much with time. In this case, the bubble size ranges from 2.7 to 4 mm because the mass-transfer enhancement factor is on the order of unity, as a result of the relatively low pH. The pH history resulting from the numerical model is compared to that obtained from a simple macroscopic model. It is found that numerical results obtained from the case in which the bubble size is solved agree well with the simple model. The observed differences between the simple model and the simulated results obtained with constant bubble size are due to the lack of coupling of mass transfer and fluid flow. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800233y

Numerical analysis of the effect of gas sparging on bubble column hydrodynamics / Wei Bai in Industrial & engineering chemistry research, Vol. 50 N° 8 (Avril 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 8 (Avril 2011) . - pp. 4320–4328 Titre : Numerical analysis of the effect of gas sparging on bubble column hydrodynamics Type de document : texte imprimé Auteurs : Wei Bai, Auteur ; Niels G. Deen, Auteur ; J. A. M. Kuipers, Auteur Année de publication : 2011 Article en page(s) : pp. 4320–4328 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Numerical  analysis  Gas Résumé : A discrete bubble model (DBM) has been used to study the effect of gas sparger properties on the hydrodynamics in a bubble column. As a first step the performance of the model was evaluated by comparison with experimental data. Subsequently, four different perforated plates with different sparged areas were used as a gas sparger. Distributions of liquid velocity, turbulent kinetic energy, and void fraction in the central plane were compared for the four different systems. Furthermore, the effect of the sparger location was also investigated. It was found that the liquid-phase circulation becomes more pronounced as the sparged area location is more distant from the center of the bottom plate. Finally, gas-phase residence time distributions (RTD) were obtained from the simulations. By employing standard axial dispersion model, the gas-phase mixing in the bubble column was characterized. Results show that the extent of mixing increased when the sparged area decreased. The axial dispersion coefficient increased as the sparged area was shifted to the edge of the bottom plate. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1017805 [article] Numerical analysis of the effect of gas sparging on bubble column hydrodynamics [texte imprimé] / Wei Bai, Auteur ; Niels G. Deen, Auteur ; J. A. M. Kuipers, Auteur . - 2011 . - pp. 4320–4328. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 8 (Avril 2011) . - pp. 4320–4328 Mots-clés : Numerical  analysis  Gas Résumé : A discrete bubble model (DBM) has been used to study the effect of gas sparger properties on the hydrodynamics in a bubble column. As a first step the performance of the model was evaluated by comparison with experimental data. Subsequently, four different perforated plates with different sparged areas were used as a gas sparger. Distributions of liquid velocity, turbulent kinetic energy, and void fraction in the central plane were compared for the four different systems. Furthermore, the effect of the sparger location was also investigated. It was found that the liquid-phase circulation becomes more pronounced as the sparged area location is more distant from the center of the bottom plate. Finally, gas-phase residence time distributions (RTD) were obtained from the simulations. By employing standard axial dispersion model, the gas-phase mixing in the bubble column was characterized. Results show that the extent of mixing increased when the sparged area decreased. The axial dispersion coefficient increased as the sparged area was shifted to the edge of the bottom plate. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1017805