1.Challenges and opportunities for carbon neutrality Global carbon emissions,primarily from the use of fossil fuels,have dramatically risen since the industrial revolution,leading to an increase in global temperature ...1.Challenges and opportunities for carbon neutrality Global carbon emissions,primarily from the use of fossil fuels,have dramatically risen since the industrial revolution,leading to an increase in global temperature and negatively impacting Earth’s ecosystems.While the coronavirus disease 2019(COVID-19)pandemic’s economic downturn may have temporarily reduced emissions.展开更多
A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking （FCC） riser of rectangular cross...A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking （FCC） riser of rectangular cross-section. Rectangular nozzles with a fixed aspect ratio but different fan angles are used for the spray feeding. While our numerical simulation reveals a generic three-phase flow structure with strong three-phase interactions under rapid vaporization of sprays, this paper tends to focus on the study of the effect of nozzle fan angle on the spray coverage as well as vapor flux distribution by spray vaporization inside the riser flow. The gas-solid （air-FCC） flow is simulated using the multi-fluid method while the evaporating sprays （liquid nitrogen） are calculated using the Lagrangian trajectory method, with a strong two-way coupling between the Eulerian gas-solid flow and the Lagrangian trajectories of spray. Our simulation shows that the spray coverage is basically dominated by the spray fan angle. The spray fan angle has a very minor effect on spray penetration. The spray vaporization flux per unit area of spray coverage is highly non-linearly distributed along the spray penetration. The convection of gas-solid flow in a riser leads to a significant downward deviation of vapor generated by droplet vaporization, causing a strong recirculating wake region in the immediate downstream area of the spray.展开更多
The electrical capacitance tomography （ECT） with neural network multi-criteria image reconstruction technique （NN-MOIRT） is developed for real time imaging of a gas-solid fluidized bed using FCC particles with eva...The electrical capacitance tomography （ECT） with neural network multi-criteria image reconstruction technique （NN-MOIRT） is developed for real time imaging of a gas-solid fluidized bed using FCC particles with evaporative liquid injection. Some aspects of the fundamental characteristics of the gas-solid flow with evaporative liquid injection including real time and time averaged cross-sectional solids concentration distributions, the cross-sectional solids concentration fluctuations and the quasi-3D flow structures are studied. A two-region model and a direct image calculation are proposed to describe the dynamic behavior in both the bubble/void phase and the emulsion phase based on the tomographic images. Comparisons are made between the fundamental behaviors of the gas-solid flows with and without evaporative liquid injection for various gas velocities ranging from bubbling to turbulent fluidization regimes. Significant differences are observed in the behavior of the gas-solid flow with the evaporative liquid injection compared to the fluidized bed without liquid injection.展开更多
The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is i...The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is its application in particle-fluid systems, where the advantage of the LBM in efficiency and parallel scalability has made it superior to many other direct numerical simulation （DNS） techniques. This article intends to provide a brief review of the application of the LBM in particle-fluid systems. The numerical techniques in the LBM pertaining to simulations of particles are discussed, with emphasis on the advanced treatment for boundary conditions on the particle-fluid interface. Other numerical issues, such as the effect of the internal fluid, are also briefly described. Additionally, recent efforts in using the LBM to obtain closures for particle-fluid drag force are also reviewed.展开更多
Magnetic resonance imaging （MRI） has been used to study the behaviour Of jets at the distributor of a 50 mm diameter fluidised bed of 0.5 mm diameter poppy seeds. Two perforated-plate distributors were examined, con...Magnetic resonance imaging （MRI） has been used to study the behaviour Of jets at the distributor of a 50 mm diameter fluidised bed of 0.5 mm diameter poppy seeds. Two perforated-plate distributors were examined, containing either 10 or 14 holes, each 1 mm diameter. Ultra-fast MR imaging was able to show the transient nature of the upper parts of the jets, where discrete bubbles are formed. Imaging in 3D showed that the central jets were the longest for flow rates below minimum fluidisation. Above minimum fluidisation, the outer jets, nearest the wall of the fluidised bed, arched inward towards the central axis. In this latter case, interpretation of the time-averaged 3D image required the use of ultra-fast MR imaging to identify the approximate height above the distributor at which discrete bubbles were formed. The apparently continuous void extending along the central axis above this height in the time-averaged 3D image was thus identified, using ultra-fast MR imaging, as representing the averaged paths of released bubbles. Time-averaged MR velocity mapping was also used to identify dead zones of stationary particles resting on the distributor between the jets. The dead zones could be observed when the superficial velocity of the gas approached minimum fluidisation, but they were smaller than those observed at lower gas superficial velocity. Comparable images of a single jet through 1.2 mm diameter poppy seeds from MRI and electrical capacitance volume tomography （ECVT） are also demonstrated.展开更多
Slugging represents one of the major regimes in fluidization,which occurs in small diameter beds with large bed height-to-diameter ratio or in large diameter beds with internals that resemble multiple small diameter f...Slugging represents one of the major regimes in fluidization,which occurs in small diameter beds with large bed height-to-diameter ratio or in large diameter beds with internals that resemble multiple small diameter fluidized beds.Slug types include round-nosed slug,wall slug and square nosed slug.Studies of the slugs have been mainly focused on round-nosed or wall slugs known as half slug.typically occurring in Geldart group A particle fuidization.The square-nosed slug typically occurring for Geldart group D particles appears to be regarded as simple in its structure.The Electrical Capacitance Volume Tomogra phy(ECVT)imaging of the square-nosed slugging phenomena conducted in this study reveals otherwise.That is the structure of the square nosed slug is,in fact,complex,particularly with respect to its dynamic variation in fluidization.More broadly.this study examines experimentally the hydrodynamic character-istics of the square-nosed fluidization regime.Specifically,simultaneous measurements from multiple ECVT sensors provide non-inv asive,continuous,3.dimensional imaging of the entire flow region of the slugging bed and hence enabling the dynamic characterization of the evolution of the slugs.The analysis of the 3D images reconstructed for real time gas-solid volume fraction profile of the slugging fluidized bed indicates that there are three different zones.namely.the bottom fluidization zone,the gas slug zone,and the solid slug zone,co-existing in the bed.The three zones present different hydrodynamic characteristics during the slug evolution.It is found that varying the gas velocity of the slugging bed mainly varies the maximum length of the gas slug zone,while it only has a minor effect on the lengths of the bottom fluidization zone and solid slug zone.It also has an insignificant efect on the solid volume fraction of the three zones.展开更多
Fluidization is an important process technology and is ubiquitously present in the process industry. The phenomena of fluidization also represent one of the most fascinating fluid-particle interactive behaviors in nat...Fluidization is an important process technology and is ubiquitously present in the process industry. The phenomena of fluidization also represent one of the most fascinating fluid-particle interactive behaviors in nature that are manifested by complex, intertwining science and engineering principles. Even though it is a centuries old practice, pursuit of the fundamental understanding of fluidization has its origins in the 1940s. Since the 1960s, fluidization has been a vibrant field for fluid mechanics, particle mechanics, as well as modeling and computation. From the historical perspective, Professor Mooson Kwauk and Professor Richard Wilhelm＇s 1948 article ＂Fluidization of Solid Particles,＂ is proved to be a pioneering work that sets a stage for subsequent fundamental studies in the characteristics of fluidization. As the field has evolved over the last six decades, Professor Kwauk has been a leader of fluidization research in China and the world,展开更多
文摘1.Challenges and opportunities for carbon neutrality Global carbon emissions,primarily from the use of fossil fuels,have dramatically risen since the industrial revolution,leading to an increase in global temperature and negatively impacting Earth’s ecosystems.While the coronavirus disease 2019(COVID-19)pandemic’s economic downturn may have temporarily reduced emissions.
文摘A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking （FCC） riser of rectangular cross-section. Rectangular nozzles with a fixed aspect ratio but different fan angles are used for the spray feeding. While our numerical simulation reveals a generic three-phase flow structure with strong three-phase interactions under rapid vaporization of sprays, this paper tends to focus on the study of the effect of nozzle fan angle on the spray coverage as well as vapor flux distribution by spray vaporization inside the riser flow. The gas-solid （air-FCC） flow is simulated using the multi-fluid method while the evaporating sprays （liquid nitrogen） are calculated using the Lagrangian trajectory method, with a strong two-way coupling between the Eulerian gas-solid flow and the Lagrangian trajectories of spray. Our simulation shows that the spray coverage is basically dominated by the spray fan angle. The spray fan angle has a very minor effect on spray penetration. The spray vaporization flux per unit area of spray coverage is highly non-linearly distributed along the spray penetration. The convection of gas-solid flow in a riser leads to a significant downward deviation of vapor generated by droplet vaporization, causing a strong recirculating wake region in the immediate downstream area of the spray.
基金support of the National Science Foundation on the development of the ECT used in this study is gratefully acknowledged
文摘The electrical capacitance tomography （ECT） with neural network multi-criteria image reconstruction technique （NN-MOIRT） is developed for real time imaging of a gas-solid fluidized bed using FCC particles with evaporative liquid injection. Some aspects of the fundamental characteristics of the gas-solid flow with evaporative liquid injection including real time and time averaged cross-sectional solids concentration distributions, the cross-sectional solids concentration fluctuations and the quasi-3D flow structures are studied. A two-region model and a direct image calculation are proposed to describe the dynamic behavior in both the bubble/void phase and the emulsion phase based on the tomographic images. Comparisons are made between the fundamental behaviors of the gas-solid flows with and without evaporative liquid injection for various gas velocities ranging from bubbling to turbulent fluidization regimes. Significant differences are observed in the behavior of the gas-solid flow with the evaporative liquid injection compared to the fluidized bed without liquid injection.
文摘The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is its application in particle-fluid systems, where the advantage of the LBM in efficiency and parallel scalability has made it superior to many other direct numerical simulation （DNS） techniques. This article intends to provide a brief review of the application of the LBM in particle-fluid systems. The numerical techniques in the LBM pertaining to simulations of particles are discussed, with emphasis on the advanced treatment for boundary conditions on the particle-fluid interface. Other numerical issues, such as the effect of the internal fluid, are also briefly described. Additionally, recent efforts in using the LBM to obtain closures for particle-fluid drag force are also reviewed.
基金funded by the Engineering and Physical Sciences Research Council (Grant number EP/F041772/1)
文摘Magnetic resonance imaging （MRI） has been used to study the behaviour Of jets at the distributor of a 50 mm diameter fluidised bed of 0.5 mm diameter poppy seeds. Two perforated-plate distributors were examined, containing either 10 or 14 holes, each 1 mm diameter. Ultra-fast MR imaging was able to show the transient nature of the upper parts of the jets, where discrete bubbles are formed. Imaging in 3D showed that the central jets were the longest for flow rates below minimum fluidisation. Above minimum fluidisation, the outer jets, nearest the wall of the fluidised bed, arched inward towards the central axis. In this latter case, interpretation of the time-averaged 3D image required the use of ultra-fast MR imaging to identify the approximate height above the distributor at which discrete bubbles were formed. The apparently continuous void extending along the central axis above this height in the time-averaged 3D image was thus identified, using ultra-fast MR imaging, as representing the averaged paths of released bubbles. Time-averaged MR velocity mapping was also used to identify dead zones of stationary particles resting on the distributor between the jets. The dead zones could be observed when the superficial velocity of the gas approached minimum fluidisation, but they were smaller than those observed at lower gas superficial velocity. Comparable images of a single jet through 1.2 mm diameter poppy seeds from MRI and electrical capacitance volume tomography （ECVT） are also demonstrated.
文摘Slugging represents one of the major regimes in fluidization,which occurs in small diameter beds with large bed height-to-diameter ratio or in large diameter beds with internals that resemble multiple small diameter fluidized beds.Slug types include round-nosed slug,wall slug and square nosed slug.Studies of the slugs have been mainly focused on round-nosed or wall slugs known as half slug.typically occurring in Geldart group A particle fuidization.The square-nosed slug typically occurring for Geldart group D particles appears to be regarded as simple in its structure.The Electrical Capacitance Volume Tomogra phy(ECVT)imaging of the square-nosed slugging phenomena conducted in this study reveals otherwise.That is the structure of the square nosed slug is,in fact,complex,particularly with respect to its dynamic variation in fluidization.More broadly.this study examines experimentally the hydrodynamic character-istics of the square-nosed fluidization regime.Specifically,simultaneous measurements from multiple ECVT sensors provide non-inv asive,continuous,3.dimensional imaging of the entire flow region of the slugging bed and hence enabling the dynamic characterization of the evolution of the slugs.The analysis of the 3D images reconstructed for real time gas-solid volume fraction profile of the slugging fluidized bed indicates that there are three different zones.namely.the bottom fluidization zone,the gas slug zone,and the solid slug zone,co-existing in the bed.The three zones present different hydrodynamic characteristics during the slug evolution.It is found that varying the gas velocity of the slugging bed mainly varies the maximum length of the gas slug zone,while it only has a minor effect on the lengths of the bottom fluidization zone and solid slug zone.It also has an insignificant efect on the solid volume fraction of the three zones.
文摘Fluidization is an important process technology and is ubiquitously present in the process industry. The phenomena of fluidization also represent one of the most fascinating fluid-particle interactive behaviors in nature that are manifested by complex, intertwining science and engineering principles. Even though it is a centuries old practice, pursuit of the fundamental understanding of fluidization has its origins in the 1940s. Since the 1960s, fluidization has been a vibrant field for fluid mechanics, particle mechanics, as well as modeling and computation. From the historical perspective, Professor Mooson Kwauk and Professor Richard Wilhelm＇s 1948 article ＂Fluidization of Solid Particles,＂ is proved to be a pioneering work that sets a stage for subsequent fundamental studies in the characteristics of fluidization. As the field has evolved over the last six decades, Professor Kwauk has been a leader of fluidization research in China and the world,
