The flow is assumed to be potential, and a boundary integral method is used to solve the Laplace equation for the velocity potential to investigate the shape and the position of the bubble. A 3D code to study the bubb...The flow is assumed to be potential, and a boundary integral method is used to solve the Laplace equation for the velocity potential to investigate the shape and the position of the bubble. A 3D code to study the bubble dynamics is developed, and the calculation results agree well with the experimental data. Numerical analyses are carried out for the interaction between multiple bubbles near the free surface including in-phase and out-of-phase bubbles. The calculation result shows that the bubble period increases with the decrease of the distance between bubble centres because of the depression effect between multiple bubbles. The depression has no relationship with the free surface and it is more apparent for out-of-phase bubbles. There are great differences in dynamic behaviour between the in-phase bubbles and the out-of-phase bubbles due to the depression effect. Furthermore, the interaction among eight bubbles is simulated with a three-dlmensional model, and the evolving process and the relevant physical phenomena are presented. These phenomena can give a reference to the future work on the power of bubbles induced by multiple charges exploding simultaneously or continuously.展开更多
In nature,cavitation bubbles typically appear in clusters,engaging in interactions that create a variety of dynamicmotion patterns.To better understand the behavior ofmultiple bubble collapses and the mechanisms of in...In nature,cavitation bubbles typically appear in clusters,engaging in interactions that create a variety of dynamicmotion patterns.To better understand the behavior ofmultiple bubble collapses and the mechanisms of interbubble interaction,this study employs molecular dynamics simulation combined with a coarse-grained force field.By focusing on collapsemorphology,local density,and pressure,it elucidates how the number and arrangement of bubbles influence the collapse process.The mechanisms behind inter-bubble interactions are also considered.The findings indicate that the collapse speed of unbounded bubbles located in lateral regions is greater than that of the bubbles in the center.Moreover,it is shown that asymmetrical bubble distributions lead to a shorter collapse time overall.展开更多
Airlift reactors are used in a wide range of industries,such as hydrometallurgy,biochemical processes,chemical process industry and wastewater treatment.Despite the simple structure of airlift reactors,the flow field ...Airlift reactors are used in a wide range of industries,such as hydrometallurgy,biochemical processes,chemical process industry and wastewater treatment.Despite the simple structure of airlift reactors,the flow field becomes complex with increasing gas velocity,and gas bubbles in the circulating regime can be observed in practice.In this paper,a numerical modelling method based on computational fluid dynamics(CFD)is presented for gas-liquid flow in airlift reactors under different bubble recirculation regimes.Gas-liquid flow was modelled using the Eulerian two-fluid equations,and extra user defined subroutines were incorporated to consider the complex physics,such as bubble-induced turbulence and turbulent dispersion force.Some alternative correlations for drag coefficient were tested to compare their ability to capture the bubble distributions in the riser and downcomer of the airlift reactors,with consideration of the interaction between bubbles.A model including multiple bubble sizes was applied to obtain more accurate simulation results of gas holdup and water velocity.Also,the use of the inhomogeneous multiple-size-group(MUSIG)model was explored as a way to better predict the complex flow regimes.The modelling method was applied to a laboratory internal loop airlift reactor,and the simulation results were compared with the published experimental measurements for gas holdup and water velocity.Reasonable agreement was obtained over a range of operating conditions,and an improvement was demonstrated using the proposed method.The simulations have shown that the inhomogeneous MUSIG model is a suitable tool to describe the complex gas-liquid interaction in the airlift reactor at a high gas superficial velocity.展开更多
The increasing attention on Bitcoin since 2013 prompts the issue of possible evidence for a causal relationship between the Bitcoin market and internet attention.Taking the Google search volume index as the measure of...The increasing attention on Bitcoin since 2013 prompts the issue of possible evidence for a causal relationship between the Bitcoin market and internet attention.Taking the Google search volume index as the measure of internet attention,time-varying Granger causality between the global Bitcoin market and internet attention is examined.Empirical results show a strong Granger causal relationship between internet attention and trading volume.Moreover,they indicate,beginning in early 2018,an even stronger impact of trading volume on internet attention,which is consistent with the rapid increase in Bitcoin users following the 2017 Bitcoin bubble.Although Bitcoin returns are found to strongly affect internet attention,internet attention only occasionally affects Bitcoin returns.Further investigation reveals that interactions between internet attention and returns can be amplified by extreme changes in prices,and internet attention is more likely to lead to returns during Bitcoin bubbles.These empirical findings shed light on cryptocurrency investor attention theory and imply trading strategy in Bitcoin markets.展开更多
Smoothed particle hydrodynamics(SPH)is a Lagrangian,mesh-free numerical method renowned for its ability to handle fluid dynamics problems with large interface deformations and multiphase flow coupling.This study intro...Smoothed particle hydrodynamics(SPH)is a Lagrangian,mesh-free numerical method renowned for its ability to handle fluid dynamics problems with large interface deformations and multiphase flow coupling.This study introduces an SPH-based multiphase flow model for simulating bubbly flows involving various immiscible fluids.The model uses a volume-based density discretization equation,ensuring numerical accuracy near interfaces,independent of density ratios,thus maintaining accuracy and stability even at high density ratios.By integrating the Continuous Surface Force method for surface tension into the multiphase SPH model,the study simulates interfacial behavior between phases.The model accurately predicts Laplace pressure differences across interfaces,maintaining interface stability at density ratios up to 100.0.Simulations of single and double bubble ascents elucidate the influence of the Bond number on bubble shape,rising distance,and velocity.As the Bond number increases,bubbles flatten and develop tails,affecting their integrity.The study also simulates multiple bubbles ascents in water,showcasing the model's ability to capture complex interfacial behaviors in bubbly flows,including deformation,adsorption,coalescence,and tearing.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No50779007)
文摘The flow is assumed to be potential, and a boundary integral method is used to solve the Laplace equation for the velocity potential to investigate the shape and the position of the bubble. A 3D code to study the bubble dynamics is developed, and the calculation results agree well with the experimental data. Numerical analyses are carried out for the interaction between multiple bubbles near the free surface including in-phase and out-of-phase bubbles. The calculation result shows that the bubble period increases with the decrease of the distance between bubble centres because of the depression effect between multiple bubbles. The depression has no relationship with the free surface and it is more apparent for out-of-phase bubbles. There are great differences in dynamic behaviour between the in-phase bubbles and the out-of-phase bubbles due to the depression effect. Furthermore, the interaction among eight bubbles is simulated with a three-dlmensional model, and the evolving process and the relevant physical phenomena are presented. These phenomena can give a reference to the future work on the power of bubbles induced by multiple charges exploding simultaneously or continuously.
基金funded by the Natural Science Foundation of China[U20A20292]Shandong Province Science andTechnology SMES InnovationAbility Improvement Project[2023TSGC0005]China Postdoctoral Science Foundation[2024M752697].
文摘In nature,cavitation bubbles typically appear in clusters,engaging in interactions that create a variety of dynamicmotion patterns.To better understand the behavior ofmultiple bubble collapses and the mechanisms of interbubble interaction,this study employs molecular dynamics simulation combined with a coarse-grained force field.By focusing on collapsemorphology,local density,and pressure,it elucidates how the number and arrangement of bubbles influence the collapse process.The mechanisms behind inter-bubble interactions are also considered.The findings indicate that the collapse speed of unbounded bubbles located in lateral regions is greater than that of the bubbles in the center.Moreover,it is shown that asymmetrical bubble distributions lead to a shorter collapse time overall.
基金support from National Key R&D Program of China(No.2021YFC2902700)pilot project of BGRIMM Technology Group(No.02-2407)special fund of National Key Laboratory of Ni&Co Associated Minerals Resources Development and Comprehensive Utilization(No.GZSYS-KY-2022-014).
文摘Airlift reactors are used in a wide range of industries,such as hydrometallurgy,biochemical processes,chemical process industry and wastewater treatment.Despite the simple structure of airlift reactors,the flow field becomes complex with increasing gas velocity,and gas bubbles in the circulating regime can be observed in practice.In this paper,a numerical modelling method based on computational fluid dynamics(CFD)is presented for gas-liquid flow in airlift reactors under different bubble recirculation regimes.Gas-liquid flow was modelled using the Eulerian two-fluid equations,and extra user defined subroutines were incorporated to consider the complex physics,such as bubble-induced turbulence and turbulent dispersion force.Some alternative correlations for drag coefficient were tested to compare their ability to capture the bubble distributions in the riser and downcomer of the airlift reactors,with consideration of the interaction between bubbles.A model including multiple bubble sizes was applied to obtain more accurate simulation results of gas holdup and water velocity.Also,the use of the inhomogeneous multiple-size-group(MUSIG)model was explored as a way to better predict the complex flow regimes.The modelling method was applied to a laboratory internal loop airlift reactor,and the simulation results were compared with the published experimental measurements for gas holdup and water velocity.Reasonable agreement was obtained over a range of operating conditions,and an improvement was demonstrated using the proposed method.The simulations have shown that the inhomogeneous MUSIG model is a suitable tool to describe the complex gas-liquid interaction in the airlift reactor at a high gas superficial velocity.
基金The paper received financial support from the National Natural Science Foundation of China(Nos.71422015,71871213)the National Center for Mathematics and Interdisciplinary Sciences,Chinese Academy of Sciences.
文摘The increasing attention on Bitcoin since 2013 prompts the issue of possible evidence for a causal relationship between the Bitcoin market and internet attention.Taking the Google search volume index as the measure of internet attention,time-varying Granger causality between the global Bitcoin market and internet attention is examined.Empirical results show a strong Granger causal relationship between internet attention and trading volume.Moreover,they indicate,beginning in early 2018,an even stronger impact of trading volume on internet attention,which is consistent with the rapid increase in Bitcoin users following the 2017 Bitcoin bubble.Although Bitcoin returns are found to strongly affect internet attention,internet attention only occasionally affects Bitcoin returns.Further investigation reveals that interactions between internet attention and returns can be amplified by extreme changes in prices,and internet attention is more likely to lead to returns during Bitcoin bubbles.These empirical findings shed light on cryptocurrency investor attention theory and imply trading strategy in Bitcoin markets.
基金the State Key Laboratory of Intelligent Optimized Manufacturing in Mining&Metallurgy Process Open Research Fund(No.JTKY202404622)and(No.BGRIMM-KZSKL-2023-12).
文摘Smoothed particle hydrodynamics(SPH)is a Lagrangian,mesh-free numerical method renowned for its ability to handle fluid dynamics problems with large interface deformations and multiphase flow coupling.This study introduces an SPH-based multiphase flow model for simulating bubbly flows involving various immiscible fluids.The model uses a volume-based density discretization equation,ensuring numerical accuracy near interfaces,independent of density ratios,thus maintaining accuracy and stability even at high density ratios.By integrating the Continuous Surface Force method for surface tension into the multiphase SPH model,the study simulates interfacial behavior between phases.The model accurately predicts Laplace pressure differences across interfaces,maintaining interface stability at density ratios up to 100.0.Simulations of single and double bubble ascents elucidate the influence of the Bond number on bubble shape,rising distance,and velocity.As the Bond number increases,bubbles flatten and develop tails,affecting their integrity.The study also simulates multiple bubbles ascents in water,showcasing the model's ability to capture complex interfacial behaviors in bubbly flows,including deformation,adsorption,coalescence,and tearing.
