This study experimentally explores the flow around a cylinder with circular cross-section placed inside a bubble plume. Small gas bubbles with diameter smaller than 0.06 mm are released from electrodes on the bottom o...This study experimentally explores the flow around a cylinder with circular cross-section placed inside a bubble plume. Small gas bubbles with diameter smaller than 0.06 mm are released from electrodes on the bottom of a water tank by electrolysis of water. The bubbles induce water flow around them as they rise because of buoyancy. Inside the generated bubble plume, a cylinder with diameter D of 30 mm is placed at 6.5D above the electrodes. The bubbles and water flow around the cylinder are visualized, and the bubble velocity distribution is measured. The experiments elucidate the bubble behavior around the cylinder, the separated shear layers originating at the cylinder surface, their roll-up, the bubble entrainment in the resultant large-scale eddies behind the cylinder, and the vortex shedding from the cylinder.展开更多
The flow patterns of the gas-liquid two-phase flow in a Moving-Bed Biofilm Reactor (MBBR) have a critical effect upon the mass transfer by the convection. Bubble plumes promote unsteadily fluctuating two-phase flows...The flow patterns of the gas-liquid two-phase flow in a Moving-Bed Biofilm Reactor (MBBR) have a critical effect upon the mass transfer by the convection. Bubble plumes promote unsteadily fluctuating two-phase flows during the aeration. This article studies the unsteady structure of bubble plumes through experiments. The time-serial bubble plume images in various cases of the tank are analyzed. The Recursive Cross Correlation-Particle Image Velocimetry (RCC-PIV) is used to calculate the velocities in those cases, and then the time-serial vortex, the total turbulence intensity, the time-serial streamline are obtained. It is shown that the aspect ratio and the void fraction are the dominant factors influencing the unsteady structure of bubble plumes. When the aspect ratio is unity and the void fraction is high, the bubble plumes see a symmetrical vortex structure with a long residence time, which is beneficial for optimizing the aeration system and enhancing the applied range of bubble plumes.展开更多
The movement of the bubble plume plays an important role in the operation of a moving bed biofilm reactor (MBBR), and it directly affects the contact and the mixture of the gas-liquid-solid phases in the aeration ta...The movement of the bubble plume plays an important role in the operation of a moving bed biofilm reactor (MBBR), and it directly affects the contact and the mixture of the gas-liquid-solid phases in the aeration tank and also the oxygen transfer from the gas phase to the liquid phase. In this study, the velocity field is determined by a 4-frame PTV as well as the time-averaged and timedependent velocity distributions. The velocity distribution of the bubble plume is analyzed to evaluate the operating efficiency of the MBBR. The results show that the aeration rate is one of the main factors that sway the velocity distribution of the bubble plumes and affect the operating efficiency of the reactor.展开更多
The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator(SSAS) developed based on optimization of the Helmholtz–Kirchhoff–Fresnel(HKF) method....The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator(SSAS) developed based on optimization of the Helmholtz–Kirchhoff–Fresnel(HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS(MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall–Novarini model and optimized HKF method. The extended Hall–Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests(CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.展开更多
To confirm the seabed fluid flow at the Haima cold seeps,an integrated study of multi-beam and seismic data reveals the morphology and fate of four bubble plumes and investigates the detailed subsurface structure of t...To confirm the seabed fluid flow at the Haima cold seeps,an integrated study of multi-beam and seismic data reveals the morphology and fate of four bubble plumes and investigates the detailed subsurface structure of the active seepage area.The shapes of bubble plumes are not constant and influenced by the northeastward bottom currents,but the water depth where these bubble plumes disappear(630–650 m below the sea level)(mbsl)is very close to the upper limit of the gas hydrate stability zone in the water column(620 m below the sea level),as calculated from the CTD data within the study area,supporting the“hydrate skin”hypothesis.Gas chimneys directly below the bottom simulating reflectors,found at most sites,are speculated as essential pathways for both thermogenic gas and biogenic gas migrating from deep formations to the gas hydrate stability zone.The fracture network on the top of the basement uplift may be heavily gas-charged,which accounts for the chimney with several kilometers in diameter(beneath Plumes B and C).The much smaller gas chimney(beneath Plume D)may stem from gas saturated localized strong permeability zone.High-resolution seismic profiles reveal pipe-like structures,characterized by stacked localized amplitude anomalies,just beneath all the plumes,which act as the fluid conduits conveying gas from the gas hydrate-bearing sediments to the seafloor,feeding the gas plumes.The differences between these pipe-like structures indicate the dynamic process of gas seepage,which may be controlled by the build-up and dissipation of pore pressure.The 3D seismic data show high saturated gas hydrates with high RMS amplitude tend to cluster on the periphery of the gas chimney.Understanding the fluid migration and hydrate accumulation pattern of the Haima cold seeps can aid in the further exploration and study on the dynamic gas hydrate system in the South China Sea.展开更多
The bubble plume is an important flow phenomenon, ubiquitous in many fields. The non-uniform bubbles in a plume are often simply considered as uniform and moving with a same slip velocity in an integral model. This st...The bubble plume is an important flow phenomenon, ubiquitous in many fields. The non-uniform bubbles in a plume are often simply considered as uniform and moving with a same slip velocity in an integral model. This study aims to have a better understanding of the behavior of the non-uniform bubbles in a plume. A set of experiments are conducted in a transparent water tank, in which the air plumes are generated through different injectors to vary the spectrum of the bubble size. The shadow images of the bubbles are simultaneously recorded with the illumination of a plane backlight. The algorithm used in the image analysis for tracing the bubbles is a newly developed multi-frame method based on the predictor-corrector method, with a good accuracy in estimating the size and the velocity of the overlapped bubbles based on the bubble shadow images. The bubbles are divided into several groups by their equivalent diameters with an interval of 0.5 mm. The spectrums of the bubble size and the void fraction are measured. It is found that the bubbles of different sizes show different dynamics features, resulting in a difference in the radial distribution. It is shown that the large bubbles gather in the center of the plume, while the medium bubbles spread the widest and even wider than the small bubbles. The difference can be explained by the effects of the transverse lift force and the amplitude of the bubble oscillation.展开更多
Three lance designs for argon bubbling in molten steel are presented. Bottom</span><span style="font-family:Verdana;"> bubbling is considered too. Geometries considered are straight-shaped, ...Three lance designs for argon bubbling in molten steel are presented. Bottom</span><span style="font-family:Verdana;"> bubbling is considered too. Geometries considered are straight-shaped, T-shaped, and disk-shaped. The bubbling behavior of these lances is analyzed using Computational Fluid Dynamics, so transient three dimensional, isothermal, two-phase, numerical simulations were carried out. Using the numerical results, the bubble distribution and the open eye area are analyzed for the considered lance geometries. The plume volume is calculated from the open eye </span><span style="font-family:Verdana;">area </span><span style="font-family:Verdana;">and the lance immersion depth using geometrical considerations. Among the three lance designs considered, disk-shaped lance has the bigger plume volume and the smaller mixing time. As the injection lance is deeper immersed</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the power stirring is increased and the mixing time is de</span><span style="font-family:Verdana;">creased.展开更多
文摘This study experimentally explores the flow around a cylinder with circular cross-section placed inside a bubble plume. Small gas bubbles with diameter smaller than 0.06 mm are released from electrodes on the bottom of a water tank by electrolysis of water. The bubbles induce water flow around them as they rise because of buoyancy. Inside the generated bubble plume, a cylinder with diameter D of 30 mm is placed at 6.5D above the electrodes. The bubbles and water flow around the cylinder are visualized, and the bubble velocity distribution is measured. The experiments elucidate the bubble behavior around the cylinder, the separated shear layers originating at the cylinder surface, their roll-up, the bubble entrainment in the resultant large-scale eddies behind the cylinder, and the vortex shedding from the cylinder.
基金Project supported by the National Natural Science Foundation of China(Grant No.51076130)the National Basic Research Program of China(973 Program,Grant No.2011CB403305)
文摘The flow patterns of the gas-liquid two-phase flow in a Moving-Bed Biofilm Reactor (MBBR) have a critical effect upon the mass transfer by the convection. Bubble plumes promote unsteadily fluctuating two-phase flows during the aeration. This article studies the unsteady structure of bubble plumes through experiments. The time-serial bubble plume images in various cases of the tank are analyzed. The Recursive Cross Correlation-Particle Image Velocimetry (RCC-PIV) is used to calculate the velocities in those cases, and then the time-serial vortex, the total turbulence intensity, the time-serial streamline are obtained. It is shown that the aspect ratio and the void fraction are the dominant factors influencing the unsteady structure of bubble plumes. When the aspect ratio is unity and the void fraction is high, the bubble plumes see a symmetrical vortex structure with a long residence time, which is beneficial for optimizing the aeration system and enhancing the applied range of bubble plumes.
基金supported by the National Natural Science Foun-dation of China(Grant No.51076130)
文摘The movement of the bubble plume plays an important role in the operation of a moving bed biofilm reactor (MBBR), and it directly affects the contact and the mixture of the gas-liquid-solid phases in the aeration tank and also the oxygen transfer from the gas phase to the liquid phase. In this study, the velocity field is determined by a 4-frame PTV as well as the time-averaged and timedependent velocity distributions. The velocity distribution of the bubble plume is analyzed to evaluate the operating efficiency of the MBBR. The results show that the aeration rate is one of the main factors that sway the velocity distribution of the bubble plumes and affect the operating efficiency of the reactor.
文摘The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator(SSAS) developed based on optimization of the Helmholtz–Kirchhoff–Fresnel(HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS(MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall–Novarini model and optimized HKF method. The extended Hall–Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests(CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.
基金The Shandong Province “Taishan Scholar” Construction Projectthe fund of the Laboratory for Marine Mineral Resources,Pilot National Laboratory for Marine Science and Technology (Qingdao) under contract No.MMRKF201810+1 种基金the National Natural Science Foundation of China under contract No.41606077the National Key R&D Program of China under contract No.2018YFC0310000.
文摘To confirm the seabed fluid flow at the Haima cold seeps,an integrated study of multi-beam and seismic data reveals the morphology and fate of four bubble plumes and investigates the detailed subsurface structure of the active seepage area.The shapes of bubble plumes are not constant and influenced by the northeastward bottom currents,but the water depth where these bubble plumes disappear(630–650 m below the sea level)(mbsl)is very close to the upper limit of the gas hydrate stability zone in the water column(620 m below the sea level),as calculated from the CTD data within the study area,supporting the“hydrate skin”hypothesis.Gas chimneys directly below the bottom simulating reflectors,found at most sites,are speculated as essential pathways for both thermogenic gas and biogenic gas migrating from deep formations to the gas hydrate stability zone.The fracture network on the top of the basement uplift may be heavily gas-charged,which accounts for the chimney with several kilometers in diameter(beneath Plumes B and C).The much smaller gas chimney(beneath Plume D)may stem from gas saturated localized strong permeability zone.High-resolution seismic profiles reveal pipe-like structures,characterized by stacked localized amplitude anomalies,just beneath all the plumes,which act as the fluid conduits conveying gas from the gas hydrate-bearing sediments to the seafloor,feeding the gas plumes.The differences between these pipe-like structures indicate the dynamic process of gas seepage,which may be controlled by the build-up and dissipation of pore pressure.The 3D seismic data show high saturated gas hydrates with high RMS amplitude tend to cluster on the periphery of the gas chimney.Understanding the fluid migration and hydrate accumulation pattern of the Haima cold seeps can aid in the further exploration and study on the dynamic gas hydrate system in the South China Sea.
基金supported by the State Key Laboratory of Hydroscience and Engineering,Tsinghua University(Grant No.2022-KY-05).
文摘The bubble plume is an important flow phenomenon, ubiquitous in many fields. The non-uniform bubbles in a plume are often simply considered as uniform and moving with a same slip velocity in an integral model. This study aims to have a better understanding of the behavior of the non-uniform bubbles in a plume. A set of experiments are conducted in a transparent water tank, in which the air plumes are generated through different injectors to vary the spectrum of the bubble size. The shadow images of the bubbles are simultaneously recorded with the illumination of a plane backlight. The algorithm used in the image analysis for tracing the bubbles is a newly developed multi-frame method based on the predictor-corrector method, with a good accuracy in estimating the size and the velocity of the overlapped bubbles based on the bubble shadow images. The bubbles are divided into several groups by their equivalent diameters with an interval of 0.5 mm. The spectrums of the bubble size and the void fraction are measured. It is found that the bubbles of different sizes show different dynamics features, resulting in a difference in the radial distribution. It is shown that the large bubbles gather in the center of the plume, while the medium bubbles spread the widest and even wider than the small bubbles. The difference can be explained by the effects of the transverse lift force and the amplitude of the bubble oscillation.
文摘Three lance designs for argon bubbling in molten steel are presented. Bottom</span><span style="font-family:Verdana;"> bubbling is considered too. Geometries considered are straight-shaped, T-shaped, and disk-shaped. The bubbling behavior of these lances is analyzed using Computational Fluid Dynamics, so transient three dimensional, isothermal, two-phase, numerical simulations were carried out. Using the numerical results, the bubble distribution and the open eye area are analyzed for the considered lance geometries. The plume volume is calculated from the open eye </span><span style="font-family:Verdana;">area </span><span style="font-family:Verdana;">and the lance immersion depth using geometrical considerations. Among the three lance designs considered, disk-shaped lance has the bigger plume volume and the smaller mixing time. As the injection lance is deeper immersed</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the power stirring is increased and the mixing time is de</span><span style="font-family:Verdana;">creased.