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Chris L Hoxie - One of the best experts on this subject based on the ideXlab platform.
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experimental study of interfacial structure of horizontal air water two phase flow in a 101 6 mm id pipe
Experimental Thermal and Fluid Science, 2018Co-Authors: Ran Kong, Adam Rau, Joe Gamber, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The current work seeks to investigate the interfacial structure and establish an extensive experimental database in horizontal air–water two-phase flow in a 101.6 mm inner diameter pipe. A wide range of flow configurations are studied including bubbly, plug and Slug flows. A flow visualization study using the high-speed video camera enables qualitative description of bubbly-to-plug and bubbly-to-Slug transitions, while the database of local time-averaged two-phase flow parameters obtained by the four-sensor conductivity probe enables quantitative study on the evolution of the flow. Detailed measurements across the flow area are performed for nine test conditions at three different axial locations downstream of the inlet. Using this database, the effects of superficial liquid and gas velocities, and development length on the evolution of interfacial structure are investigated. Similar characteristics are observed as in a counterpart 38 mm ID horizontal two-phase flow facility, which include (1) the bubbles are found to be more concentrated near the top wall in bubbly flow as superficial liquid velocity decreases at a constant superficial gas velocity, while increasing superficial gas velocity promotes the growth of bubble layer thickness; (2) in bubbly-to-plug transition, the void fraction of small bubbles decreases and the size of small bubbles increases, while in bubbly-to-Slug transition, opposite trends are observed. Meanwhile, different characteristics on the evolution of the interfacial structure are also observed, which indicates the effect of increasing pipe diameter. The bubbly-to-plug/Slug transition is found to shift to higher superficial liquid velocities as pipe diameter increases. It is observed that the gas phase is more concentrated near the top wall in the large diameter pipe. As a result, the distance between bubbles is smaller and there is a higher chance for bubbles to coalesce into large bubbles. The critical void fraction where the bubbly-to-plug/Slug transition initiates decreases as pipe size increases.
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Experimental study of horizontal air-water plug-to-Slug transition flow in different pipe sizes
International Journal of Heat and Mass Transfer, 2018Co-Authors: Ran Kong, Adam Rau, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The current work investigates the plug-to-Slug transition in horizontal air–water two-phase flow in small (38.1 mm) and large (101.6 mm) diameter pipes. An extensive database is established to study the local interfacial structure in plug-to-Slug transition flow. Detailed measurements across the flow area are performed for nine and six test conditions in small and large pipes, respectively, at three different axial locations downstream of the inlet using the local four-sensor conductivity probe. The effects of jg, jf, development length and pipe size are investigated. It is found that the number of small bubbles in the liquid plug/Slug increases significantly in plug-to-Slug transition with increasing jg, which are generated by the strong shear between the gas Slug and liquid film. Due to the relative motion, these small bubbles either coalesce with the nose of the following plug/Slug bubble, or slide between the plug/Slug bubble and the wall, and then travel around the pipe circumference to reside beneath the large bubbles. This explains the large number of small bubbles observed at the top of the liquid film for the conditions at high gas flow rates. In the process of traveling downwards, some of the small bubbles coalesce with the Slug bubbles. It is also found that increasing jg or jf decreases the size of the small bubbles. While shearing-off is believed to dominate as jg increases, turbulent-impact is enhanced as jf increases due to the increasing turbulence level in the liquid phase. Increasing jg, development length, or decreasing jf slightly increases the depths of the plug/Slug bubbles; however, significant growth of plug/Slug bubbles is observed in the axial direction. For the same condition, the contribution from large bubbles to total void fraction increases as pipe size increases, while the distribution of total void fraction is similar. The size of both small and large bubbles is found to be larger in the large diameter pipe. Due to the current bubble injection mechanism, small bubbles are generated at the inlet; they coalesce into large bubbles as the flow develops. The large bubble is found to accelerate as it grows along the axial direction, which can lead to a decreasing void fraction although pressure keeps decreasing.
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Void fraction prediction and one-dimensional drift-flux analysis for horizontal two-phase flow in different pipe sizes
Experimental Thermal and Fluid Science, 2018Co-Authors: Ran Kong, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Qingzi Zhu, Mamoru Ishii, Chris L HoxieAbstract:Abstract The current work seeks to perform the one-dimensional drift-flux analysis for horizontal gas-dispersed flow, to provide closure models for void fraction and to investigate the relative motion between gas and liquid phases. A reliable experimental database for void fraction and bubble velocity is first established over a wide range of flow conditions for bubbly, plug and Slug flows in different pipe sizes, due to the limitations of existing database. It is found that the effects of flow regime and pipe size on the drift-flux analysis are insignificant. The drift velocity is found to be negative in horizontal bubbly flow. This is consistent with the conclusion by the 〈α〉–〈β〉 analysis, where the slope is found to be greater than one. This indicates that the gas phase moves slower than the liquid phase in horizontal bubbly flow. The analysis also indicates that the horizontal plug and Slug flows are relatively more homogeneous than horizontal bubbly flow. As such, the homogeneous flow model can predict the void fraction better for plug and Slug flows. The current drift-flux analysis provides closure relations for C0 and 〈〈Vgj〉〉 that can be employed in TRACE, while existing closure relations are developed for vertical flow and cannot be used for horizontal flow prediction. In addition, various void fraction models in literature are evaluated. It is found that the correlations modified from vertical flow generally cannot predict the void fraction well for horizontal flow. The correlations for plug and Slug flows by Franca and Lahey, and Lamari underestimate the void fraction, which may be because these correlations are developed for relatively low jf conditions, while the current work focuses on conditions at jf greater than 2.0 m/s.
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experimental investigation of horizontal air water bubbly to plug and bubbly to Slug transition flows in a 3 81 cm id pipe
International Journal of Multiphase Flow, 2017Co-Authors: Ran Kong, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The present study seeks to investigate horizontal bubbly-to-plug and bubbly-to-Slug transition flows. The two-phase flow structures and transition mechanisms in these transition flows are studied based on experimental database established using the local four-sensor conductivity probe in a 3.81 cm inner diameter pipe. While Slug flow needs to be distinguished from plug flow due to the presence of large number of small bubbles (and thus, large interfacial area concentration), both differences and similarities are observed in the evolution of interfacial structures in bubbly-to-plug and bubbly-to-Slug transitions. The bubbly-to-plug transition is studied by decreasing the liquid flow rate at a fixed gas flow rate. It is found that as the liquid flow rate is lowered, bubbles pack near the top wall of the pipe due to the diminished role of turbulent mixing. As the flow rate is lowered further, bubbles begin to coalesce and form the large bubbles characteristic of plug flow. Bubble size increases while bubble velocity decreases as liquid flow rate decreases, and the profile of the bubble velocity changes its shape due to the changing interfacial structure. The bubbly-to-Slug transition is investigated by increasing the gas flow rate at a fixed liquid flow rate. In this transition, gas phase becomes more uniformly distributed throughout the cross-section due to the formation of large bubbles and the increasing bubble-induced turbulence. The size of small bubbles decreases while bubble velocity increases as gas flow rate increases. The distributions of bubble size and bubble velocity become more symmetric in this transition. While differences are observed in these two transitions, similarities are also noticed. As bubbly-to-plug or bubbly-to-Slug transition occurs, the formation of large elongated bubbles is observed not in the uppermost region of bubble layer, but in a lower region. At the beginning of transitions, relative differences in phase velocities near the top of the pipe cross-section to those near the pipe center become larger for both gas and liquid phases, because more densely packed bubbles introduce more resistance to both phases.
A Arabi - One of the best experts on this subject based on the ideXlab platform.
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Slug frequency for a gas liquid plug flow review and development of a new correlation
International Communications in Heat and Mass Transfer, 2020Co-Authors: A Arabi, Y Salhi, Karim Ragui, Abdelkader FilaliAbstract:Abstract Slug frequency is one of the most important parameters for designing industrial installations where intermittent gas-liquid flows could be found. Thus, the literature is found full of various experimental investigations and developed empirical correlations to predict such parameter. Nevertheless, the effect of intermittent flow sub-regimes on Slug frequencies remains an open issue, especially in the case of plug flow. Hence, the present work is devoted to providing an update review and analysis of the Slug frequency in plug flow case. For this purpose, data from previous experiments have been collected and deeply examined. It was found that the increase in liquid superficial velocity and the decrease in pipe diameter could induce an increase of plug frequency. The comparison between experimental data and the predictions of twenty available empirical models showed that the correlations based on Strouhal number and input liquid fraction are the best ones that predict well the experimental plug frequency. However, each correlation is found to be valid for a limited range close to the data's conditions that were used for its development. As such, and by considering an extended range of the whole available experimental database, a new empirical correlation has been proposed.
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on gas liquid intermittent flow in a horizontal pipe influence of sub regime on Slug frequency
Chemical Engineering Science, 2020Co-Authors: A Arabi, Y Salhi, Y Zenati, Elkhider Siahmed, Jack LegrandAbstract:Abstract Among the intrinsic parameters identified in intermittent gas-liquid flows; Slug frequency is known as the most complicated one to model. The present work concerns the investigation of Slug frequency for various sub-regimes which might be found in intermittent flow. Experiments, near atmospheric pressure conditions, were carried out in a 13-meter long horizontal pipe with a 30 mm inside diameter. The study involved plug regime, less aerated Slug and highly aerated Slug flows. Comparison between different methods of Slug frequency quantification, from pressure drop signal, was performed with counting, Wilkens & Thomas as well as the Power Spectral Density (PSD) methods. PSD was found to be the best method for Slug frequency measurements. A new flow map, using dimensionless numbers as coordinates for the sub-regimes distinction, was established. After performing substantial comparisons between the present results and models available in the literature a new correlation is proposed including the sub-regime types.
Abdelkader Filali - One of the best experts on this subject based on the ideXlab platform.
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Slug frequency for a gas liquid plug flow review and development of a new correlation
International Communications in Heat and Mass Transfer, 2020Co-Authors: A Arabi, Y Salhi, Karim Ragui, Abdelkader FilaliAbstract:Abstract Slug frequency is one of the most important parameters for designing industrial installations where intermittent gas-liquid flows could be found. Thus, the literature is found full of various experimental investigations and developed empirical correlations to predict such parameter. Nevertheless, the effect of intermittent flow sub-regimes on Slug frequencies remains an open issue, especially in the case of plug flow. Hence, the present work is devoted to providing an update review and analysis of the Slug frequency in plug flow case. For this purpose, data from previous experiments have been collected and deeply examined. It was found that the increase in liquid superficial velocity and the decrease in pipe diameter could induce an increase of plug frequency. The comparison between experimental data and the predictions of twenty available empirical models showed that the correlations based on Strouhal number and input liquid fraction are the best ones that predict well the experimental plug frequency. However, each correlation is found to be valid for a limited range close to the data's conditions that were used for its development. As such, and by considering an extended range of the whole available experimental database, a new empirical correlation has been proposed.
Ran Kong - One of the best experts on this subject based on the ideXlab platform.
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experimental study of interfacial structure of horizontal air water two phase flow in a 101 6 mm id pipe
Experimental Thermal and Fluid Science, 2018Co-Authors: Ran Kong, Adam Rau, Joe Gamber, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The current work seeks to investigate the interfacial structure and establish an extensive experimental database in horizontal air–water two-phase flow in a 101.6 mm inner diameter pipe. A wide range of flow configurations are studied including bubbly, plug and Slug flows. A flow visualization study using the high-speed video camera enables qualitative description of bubbly-to-plug and bubbly-to-Slug transitions, while the database of local time-averaged two-phase flow parameters obtained by the four-sensor conductivity probe enables quantitative study on the evolution of the flow. Detailed measurements across the flow area are performed for nine test conditions at three different axial locations downstream of the inlet. Using this database, the effects of superficial liquid and gas velocities, and development length on the evolution of interfacial structure are investigated. Similar characteristics are observed as in a counterpart 38 mm ID horizontal two-phase flow facility, which include (1) the bubbles are found to be more concentrated near the top wall in bubbly flow as superficial liquid velocity decreases at a constant superficial gas velocity, while increasing superficial gas velocity promotes the growth of bubble layer thickness; (2) in bubbly-to-plug transition, the void fraction of small bubbles decreases and the size of small bubbles increases, while in bubbly-to-Slug transition, opposite trends are observed. Meanwhile, different characteristics on the evolution of the interfacial structure are also observed, which indicates the effect of increasing pipe diameter. The bubbly-to-plug/Slug transition is found to shift to higher superficial liquid velocities as pipe diameter increases. It is observed that the gas phase is more concentrated near the top wall in the large diameter pipe. As a result, the distance between bubbles is smaller and there is a higher chance for bubbles to coalesce into large bubbles. The critical void fraction where the bubbly-to-plug/Slug transition initiates decreases as pipe size increases.
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Experimental study of horizontal air-water plug-to-Slug transition flow in different pipe sizes
International Journal of Heat and Mass Transfer, 2018Co-Authors: Ran Kong, Adam Rau, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The current work investigates the plug-to-Slug transition in horizontal air–water two-phase flow in small (38.1 mm) and large (101.6 mm) diameter pipes. An extensive database is established to study the local interfacial structure in plug-to-Slug transition flow. Detailed measurements across the flow area are performed for nine and six test conditions in small and large pipes, respectively, at three different axial locations downstream of the inlet using the local four-sensor conductivity probe. The effects of jg, jf, development length and pipe size are investigated. It is found that the number of small bubbles in the liquid plug/Slug increases significantly in plug-to-Slug transition with increasing jg, which are generated by the strong shear between the gas Slug and liquid film. Due to the relative motion, these small bubbles either coalesce with the nose of the following plug/Slug bubble, or slide between the plug/Slug bubble and the wall, and then travel around the pipe circumference to reside beneath the large bubbles. This explains the large number of small bubbles observed at the top of the liquid film for the conditions at high gas flow rates. In the process of traveling downwards, some of the small bubbles coalesce with the Slug bubbles. It is also found that increasing jg or jf decreases the size of the small bubbles. While shearing-off is believed to dominate as jg increases, turbulent-impact is enhanced as jf increases due to the increasing turbulence level in the liquid phase. Increasing jg, development length, or decreasing jf slightly increases the depths of the plug/Slug bubbles; however, significant growth of plug/Slug bubbles is observed in the axial direction. For the same condition, the contribution from large bubbles to total void fraction increases as pipe size increases, while the distribution of total void fraction is similar. The size of both small and large bubbles is found to be larger in the large diameter pipe. Due to the current bubble injection mechanism, small bubbles are generated at the inlet; they coalesce into large bubbles as the flow develops. The large bubble is found to accelerate as it grows along the axial direction, which can lead to a decreasing void fraction although pressure keeps decreasing.
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Void fraction prediction and one-dimensional drift-flux analysis for horizontal two-phase flow in different pipe sizes
Experimental Thermal and Fluid Science, 2018Co-Authors: Ran Kong, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Qingzi Zhu, Mamoru Ishii, Chris L HoxieAbstract:Abstract The current work seeks to perform the one-dimensional drift-flux analysis for horizontal gas-dispersed flow, to provide closure models for void fraction and to investigate the relative motion between gas and liquid phases. A reliable experimental database for void fraction and bubble velocity is first established over a wide range of flow conditions for bubbly, plug and Slug flows in different pipe sizes, due to the limitations of existing database. It is found that the effects of flow regime and pipe size on the drift-flux analysis are insignificant. The drift velocity is found to be negative in horizontal bubbly flow. This is consistent with the conclusion by the 〈α〉–〈β〉 analysis, where the slope is found to be greater than one. This indicates that the gas phase moves slower than the liquid phase in horizontal bubbly flow. The analysis also indicates that the horizontal plug and Slug flows are relatively more homogeneous than horizontal bubbly flow. As such, the homogeneous flow model can predict the void fraction better for plug and Slug flows. The current drift-flux analysis provides closure relations for C0 and 〈〈Vgj〉〉 that can be employed in TRACE, while existing closure relations are developed for vertical flow and cannot be used for horizontal flow prediction. In addition, various void fraction models in literature are evaluated. It is found that the correlations modified from vertical flow generally cannot predict the void fraction well for horizontal flow. The correlations for plug and Slug flows by Franca and Lahey, and Lamari underestimate the void fraction, which may be because these correlations are developed for relatively low jf conditions, while the current work focuses on conditions at jf greater than 2.0 m/s.
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experimental investigation of horizontal air water bubbly to plug and bubbly to Slug transition flows in a 3 81 cm id pipe
International Journal of Multiphase Flow, 2017Co-Authors: Ran Kong, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The present study seeks to investigate horizontal bubbly-to-plug and bubbly-to-Slug transition flows. The two-phase flow structures and transition mechanisms in these transition flows are studied based on experimental database established using the local four-sensor conductivity probe in a 3.81 cm inner diameter pipe. While Slug flow needs to be distinguished from plug flow due to the presence of large number of small bubbles (and thus, large interfacial area concentration), both differences and similarities are observed in the evolution of interfacial structures in bubbly-to-plug and bubbly-to-Slug transitions. The bubbly-to-plug transition is studied by decreasing the liquid flow rate at a fixed gas flow rate. It is found that as the liquid flow rate is lowered, bubbles pack near the top wall of the pipe due to the diminished role of turbulent mixing. As the flow rate is lowered further, bubbles begin to coalesce and form the large bubbles characteristic of plug flow. Bubble size increases while bubble velocity decreases as liquid flow rate decreases, and the profile of the bubble velocity changes its shape due to the changing interfacial structure. The bubbly-to-Slug transition is investigated by increasing the gas flow rate at a fixed liquid flow rate. In this transition, gas phase becomes more uniformly distributed throughout the cross-section due to the formation of large bubbles and the increasing bubble-induced turbulence. The size of small bubbles decreases while bubble velocity increases as gas flow rate increases. The distributions of bubble size and bubble velocity become more symmetric in this transition. While differences are observed in these two transitions, similarities are also noticed. As bubbly-to-plug or bubbly-to-Slug transition occurs, the formation of large elongated bubbles is observed not in the uppermost region of bubble layer, but in a lower region. At the beginning of transitions, relative differences in phase velocities near the top of the pipe cross-section to those near the pipe center become larger for both gas and liquid phases, because more densely packed bubbles introduce more resistance to both phases.
Seungjin Kim - One of the best experts on this subject based on the ideXlab platform.
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experimental study of interfacial structure of horizontal air water two phase flow in a 101 6 mm id pipe
Experimental Thermal and Fluid Science, 2018Co-Authors: Ran Kong, Adam Rau, Joe Gamber, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The current work seeks to investigate the interfacial structure and establish an extensive experimental database in horizontal air–water two-phase flow in a 101.6 mm inner diameter pipe. A wide range of flow configurations are studied including bubbly, plug and Slug flows. A flow visualization study using the high-speed video camera enables qualitative description of bubbly-to-plug and bubbly-to-Slug transitions, while the database of local time-averaged two-phase flow parameters obtained by the four-sensor conductivity probe enables quantitative study on the evolution of the flow. Detailed measurements across the flow area are performed for nine test conditions at three different axial locations downstream of the inlet. Using this database, the effects of superficial liquid and gas velocities, and development length on the evolution of interfacial structure are investigated. Similar characteristics are observed as in a counterpart 38 mm ID horizontal two-phase flow facility, which include (1) the bubbles are found to be more concentrated near the top wall in bubbly flow as superficial liquid velocity decreases at a constant superficial gas velocity, while increasing superficial gas velocity promotes the growth of bubble layer thickness; (2) in bubbly-to-plug transition, the void fraction of small bubbles decreases and the size of small bubbles increases, while in bubbly-to-Slug transition, opposite trends are observed. Meanwhile, different characteristics on the evolution of the interfacial structure are also observed, which indicates the effect of increasing pipe diameter. The bubbly-to-plug/Slug transition is found to shift to higher superficial liquid velocities as pipe diameter increases. It is observed that the gas phase is more concentrated near the top wall in the large diameter pipe. As a result, the distance between bubbles is smaller and there is a higher chance for bubbles to coalesce into large bubbles. The critical void fraction where the bubbly-to-plug/Slug transition initiates decreases as pipe size increases.
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Experimental study of horizontal air-water plug-to-Slug transition flow in different pipe sizes
International Journal of Heat and Mass Transfer, 2018Co-Authors: Ran Kong, Adam Rau, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The current work investigates the plug-to-Slug transition in horizontal air–water two-phase flow in small (38.1 mm) and large (101.6 mm) diameter pipes. An extensive database is established to study the local interfacial structure in plug-to-Slug transition flow. Detailed measurements across the flow area are performed for nine and six test conditions in small and large pipes, respectively, at three different axial locations downstream of the inlet using the local four-sensor conductivity probe. The effects of jg, jf, development length and pipe size are investigated. It is found that the number of small bubbles in the liquid plug/Slug increases significantly in plug-to-Slug transition with increasing jg, which are generated by the strong shear between the gas Slug and liquid film. Due to the relative motion, these small bubbles either coalesce with the nose of the following plug/Slug bubble, or slide between the plug/Slug bubble and the wall, and then travel around the pipe circumference to reside beneath the large bubbles. This explains the large number of small bubbles observed at the top of the liquid film for the conditions at high gas flow rates. In the process of traveling downwards, some of the small bubbles coalesce with the Slug bubbles. It is also found that increasing jg or jf decreases the size of the small bubbles. While shearing-off is believed to dominate as jg increases, turbulent-impact is enhanced as jf increases due to the increasing turbulence level in the liquid phase. Increasing jg, development length, or decreasing jf slightly increases the depths of the plug/Slug bubbles; however, significant growth of plug/Slug bubbles is observed in the axial direction. For the same condition, the contribution from large bubbles to total void fraction increases as pipe size increases, while the distribution of total void fraction is similar. The size of both small and large bubbles is found to be larger in the large diameter pipe. Due to the current bubble injection mechanism, small bubbles are generated at the inlet; they coalesce into large bubbles as the flow develops. The large bubble is found to accelerate as it grows along the axial direction, which can lead to a decreasing void fraction although pressure keeps decreasing.
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Void fraction prediction and one-dimensional drift-flux analysis for horizontal two-phase flow in different pipe sizes
Experimental Thermal and Fluid Science, 2018Co-Authors: Ran Kong, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Qingzi Zhu, Mamoru Ishii, Chris L HoxieAbstract:Abstract The current work seeks to perform the one-dimensional drift-flux analysis for horizontal gas-dispersed flow, to provide closure models for void fraction and to investigate the relative motion between gas and liquid phases. A reliable experimental database for void fraction and bubble velocity is first established over a wide range of flow conditions for bubbly, plug and Slug flows in different pipe sizes, due to the limitations of existing database. It is found that the effects of flow regime and pipe size on the drift-flux analysis are insignificant. The drift velocity is found to be negative in horizontal bubbly flow. This is consistent with the conclusion by the 〈α〉–〈β〉 analysis, where the slope is found to be greater than one. This indicates that the gas phase moves slower than the liquid phase in horizontal bubbly flow. The analysis also indicates that the horizontal plug and Slug flows are relatively more homogeneous than horizontal bubbly flow. As such, the homogeneous flow model can predict the void fraction better for plug and Slug flows. The current drift-flux analysis provides closure relations for C0 and 〈〈Vgj〉〉 that can be employed in TRACE, while existing closure relations are developed for vertical flow and cannot be used for horizontal flow prediction. In addition, various void fraction models in literature are evaluated. It is found that the correlations modified from vertical flow generally cannot predict the void fraction well for horizontal flow. The correlations for plug and Slug flows by Franca and Lahey, and Lamari underestimate the void fraction, which may be because these correlations are developed for relatively low jf conditions, while the current work focuses on conditions at jf greater than 2.0 m/s.
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experimental investigation of horizontal air water bubbly to plug and bubbly to Slug transition flows in a 3 81 cm id pipe
International Journal of Multiphase Flow, 2017Co-Authors: Ran Kong, Seungjin Kim, Stephen M Bajorek, Kirk Tien, Chris L HoxieAbstract:Abstract The present study seeks to investigate horizontal bubbly-to-plug and bubbly-to-Slug transition flows. The two-phase flow structures and transition mechanisms in these transition flows are studied based on experimental database established using the local four-sensor conductivity probe in a 3.81 cm inner diameter pipe. While Slug flow needs to be distinguished from plug flow due to the presence of large number of small bubbles (and thus, large interfacial area concentration), both differences and similarities are observed in the evolution of interfacial structures in bubbly-to-plug and bubbly-to-Slug transitions. The bubbly-to-plug transition is studied by decreasing the liquid flow rate at a fixed gas flow rate. It is found that as the liquid flow rate is lowered, bubbles pack near the top wall of the pipe due to the diminished role of turbulent mixing. As the flow rate is lowered further, bubbles begin to coalesce and form the large bubbles characteristic of plug flow. Bubble size increases while bubble velocity decreases as liquid flow rate decreases, and the profile of the bubble velocity changes its shape due to the changing interfacial structure. The bubbly-to-Slug transition is investigated by increasing the gas flow rate at a fixed liquid flow rate. In this transition, gas phase becomes more uniformly distributed throughout the cross-section due to the formation of large bubbles and the increasing bubble-induced turbulence. The size of small bubbles decreases while bubble velocity increases as gas flow rate increases. The distributions of bubble size and bubble velocity become more symmetric in this transition. While differences are observed in these two transitions, similarities are also noticed. As bubbly-to-plug or bubbly-to-Slug transition occurs, the formation of large elongated bubbles is observed not in the uppermost region of bubble layer, but in a lower region. At the beginning of transitions, relative differences in phase velocities near the top of the pipe cross-section to those near the pipe center become larger for both gas and liquid phases, because more densely packed bubbles introduce more resistance to both phases.
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characterization of horizontal air water two phase flow in a round pipe part i flow visualization
International Journal of Multiphase Flow, 2015Co-Authors: Justin D Talley, Seungjin Kim, Ted Worosz, John R BuchananAbstract:Abstract As a part of characterizing the bubble interaction mechanisms and flow regime transition processes in horizontal gas–liquid two-phase flow, a flow visualization study is performed in an air–water test facility constructed from 3.81 cm inner diameter clear acrylic round pipes. The test section is approximately 250 diameters in length to allow for development of the flow. Flow visualizations are performed using a high-speed video camera at 80 and 245 diameters downstream of the inlet to observe the development of the flow structures. A total of 27 flow conditions including bubbly, plug, Slug, stratified, wavy, and annular flows are characterized in the present study. In highly turbulent bubbly flow conditions it is found that the distribution becomes more uniform with increasing development length through a turbulence penetration process that counters the effect of buoyancy. It is also found that plug bubbles form below a layer of small bubbles rather than at the upper pipe wall where the bubbles are most packed. In fact, it is consistently found that turbulence-based bubble interactions do not occur in the most densely packed regions as the eddies there are not large enough to effect the bubbles. Rather, bubble packing-induced coalescence occurs in these regions and contributes to the formation of plug bubbles. The newly formed plug bubbles move faster than, and ultimately pass, the smaller bubbles above due to the effect of the wall. These small bubbles are subsequently overtaken by the following plug bubble and coalesce with the nose region through a process denoted as drag-induced coalescence.