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Dual-frequency severe slugging in horizontal pipeline-riser systems / Reza Malekzadeh in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Titre : Dual-frequency severe slugging in horizontal pipeline-riser systems Type de document : texte imprimé Auteurs : Reza Malekzadeh, Auteur ; Robert F. Mudde, Auteur ; Ruud A. W. M. Henkes, Auteur Année de publication : 2013 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : oscillations;  flow  (dynamics);  pipelines;  pipeline  risers;  water Résumé : A new type of severe slugging is found that can occur in two-phase flow of gas and liquid in pipeline-riser systems. This instability, which will be referred to as dual-frequency severe slugging (DFSS), generates a different class of flow oscillations compared to the classical severe slugging cycle, having a dominant single frequency that is commonly found in a pipe downward inclined by a few degrees from the horizontal connected to a vertical riser. The DFSS flow pattern was found in laboratory experiments carried out in a 100 m long, 50.8 mm diameter horizontal pipeline followed by a 15 m high, 50.8 mm diameter vertical riser operating at atmospheric end pressure. The experimental facility also included a 400 liter gas buffer vessel, placed upstream of the pipeline, to obtain extra pipeline compressibility. Air and water were used as the experimental fluids. At constant inflow conditions, we observed a type of severe slugging exhibiting a dual-frequency behavior. The relatively high-frequency fluctuations, which are in the order of 0.01 Hz, are related to the classical severe slugging cycle or to an unstable oscillatory process. The relatively low-frequency fluctuations, which are in the order of 0.001 Hz, are associated with the gradual cyclic transition of the system between two metastable states, i.e., severe slugging and unstable oscillations. Numerical simulations were performed using OLGA, a one-dimensional two-fluid flow model. The numerical model predicts the relatively low-frequency fluctuations associated with the DFSS flow regime. The laboratory experiments and the numerical simulations showed that the evolution of the DFSS is proportional to the length of the pipeline. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Dual-frequency severe slugging in horizontal pipeline-riser systems [texte imprimé] / Reza Malekzadeh, Auteur ; Robert F. Mudde, Auteur ; Ruud A. W. M. Henkes, Auteur . - 2013 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Mots-clés : oscillations;  flow  (dynamics);  pipelines;  pipeline  risers;  water Résumé : A new type of severe slugging is found that can occur in two-phase flow of gas and liquid in pipeline-riser systems. This instability, which will be referred to as dual-frequency severe slugging (DFSS), generates a different class of flow oscillations compared to the classical severe slugging cycle, having a dominant single frequency that is commonly found in a pipe downward inclined by a few degrees from the horizontal connected to a vertical riser. The DFSS flow pattern was found in laboratory experiments carried out in a 100 m long, 50.8 mm diameter horizontal pipeline followed by a 15 m high, 50.8 mm diameter vertical riser operating at atmospheric end pressure. The experimental facility also included a 400 liter gas buffer vessel, placed upstream of the pipeline, to obtain extra pipeline compressibility. Air and water were used as the experimental fluids. At constant inflow conditions, we observed a type of severe slugging exhibiting a dual-frequency behavior. The relatively high-frequency fluctuations, which are in the order of 0.01 Hz, are related to the classical severe slugging cycle or to an unstable oscillatory process. The relatively low-frequency fluctuations, which are in the order of 0.001 Hz, are associated with the gradual cyclic transition of the system between two metastable states, i.e., severe slugging and unstable oscillations. Numerical simulations were performed using OLGA, a one-dimensional two-fluid flow model. The numerical model predicts the relatively low-frequency fluctuations associated with the DFSS flow regime. The laboratory experiments and the numerical simulations showed that the evolution of the DFSS is proportional to the length of the pipeline. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Gas Fraction and Bubble Dynamics in Structured Slurry Bubble Columns / Nasim Hooshyar in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10689-10697 Titre : Gas Fraction and Bubble Dynamics in Structured Slurry Bubble Columns Type de document : texte imprimé Auteurs : Nasim Hooshyar, Auteur ; Peter J. Hamersma, Auteur ; Robert F. Mudde, Auteur Année de publication : 2011 Article en page(s) : pp. 10689-10697 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Particle  suspension  Bubble  column  Hydrodynamics Résumé : With the aim of structuring the flow and reducing backmixing in slurry bubble columns, we investigate the effect of needle spargers in three-phase systems. We apply optical probes in a 2D and 3D column to measure the bubble dynamics and gas fraction. Experimental results for air-water-glass beads show that an increase in solids volume fraction (1) decreases the gas fraction, (2) shifts the transition point from homogeneous to heterogeneous flow to a lower gas velocity, (3) increases the mean bubble velocity by 60-100% in the range of superficial gas velocities from 0.02 to 0.1 m/s, and (4) has only a limited effect on the bubble size distribution. Fitting our experimental data to the Richardson and Zaki and Garnier models shows that we cannot use the model coefficients they report in their papers. However, fitting our data results in realistic values for the terminal bubble velocity in a swarm. By using needle spargers, giving a very uniform gas supply, a first step toward structuring the hydrodynamics of slurry bubble columns has been taken. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447962 [article] Gas Fraction and Bubble Dynamics in Structured Slurry Bubble Columns [texte imprimé] / Nasim Hooshyar, Auteur ; Peter J. Hamersma, Auteur ; Robert F. Mudde, Auteur . - 2011 . - pp. 10689-10697. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10689-10697 Mots-clés : Particle  suspension  Bubble  column  Hydrodynamics Résumé : With the aim of structuring the flow and reducing backmixing in slurry bubble columns, we investigate the effect of needle spargers in three-phase systems. We apply optical probes in a 2D and 3D column to measure the bubble dynamics and gas fraction. Experimental results for air-water-glass beads show that an increase in solids volume fraction (1) decreases the gas fraction, (2) shifts the transition point from homogeneous to heterogeneous flow to a lower gas velocity, (3) increases the mean bubble velocity by 60-100% in the range of superficial gas velocities from 0.02 to 0.1 m/s, and (4) has only a limited effect on the bubble size distribution. Fitting our experimental data to the Richardson and Zaki and Garnier models shows that we cannot use the model coefficients they report in their papers. However, fitting our data results in realistic values for the terminal bubble velocity in a swarm. By using needle spargers, giving a very uniform gas supply, a first step toward structuring the hydrodynamics of slurry bubble columns has been taken. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447962