Single argon bubble dynamics in liquid steel under Ruhrstahl-Heraeus(RH)vacuum conditions were simulated using the volume of fluid method,and the ideal gas law was used to consider bubble growth due to heat transfer a...Single argon bubble dynamics in liquid steel under Ruhrstahl-Heraeus(RH)vacuum conditions were simulated using the volume of fluid method,and the ideal gas law was used to consider bubble growth due to heat transfer and pressure drop.Additional simulation with a constant bubble density was also performed to validate the numerical method,and the predicted terminal bubble shape and velocity were found to agree with those presented in the Grace diagram and calculated by drag correlation,respectively.The simulation results under RH conditions indicate that the terminal bubble shape and velocity cannot be reached.The primary bubble growth occurs within a rising distance of 0.3 m owing to heating by the high-temperature liquid steel;subsequently,the bubble continues to grow under equilibrium with the hydrostatic pressure.When the initial diameter is 8-32 mm,the bubble diameter and rising velocity near the liquid surface are 80-200 mm and 0.5-0.8 m/s,respectively.The bubble rises rectilinearly with an axisymmetric shape,and the shape evolution history includes an initial sphere,(dimpled)ellipsoid,and spherical cap with satellite bubbles.展开更多
In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating gro...In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating growth rather than a continuous expansion.Furthermore,a theoretical model and numerical calculation method were proposed,which revealed the dynamic mechanism of bubble growth.Good agreement between the theoretical results and experimental observations verified the general correctness and feasibility of the proposed method.展开更多
This study is concerned with the dynamic characteristics of bubbles near two connected walls(one horizontal and the other inclined with an obtuse angle from the horizontal one). In this study, we set up an experiment ...This study is concerned with the dynamic characteristics of bubbles near two connected walls(one horizontal and the other inclined with an obtuse angle from the horizontal one). In this study, we set up an experiment system to conduct typical cases, and the boundary element method is employed to explain the bubble behavior and study the effect of relative parameters. Comparing the two mutually perpendicular walls, we find that the liquid jet deviates from the horizontal direction within a much shorter range. On the intersection of the two walls, the motions of bubbles have similar trends. The relatively low pressure between the bubble and walls causes the transition of the bubble, and a local high-pressure zone leads to the formation of a liquid jet. Moreover, there are moments when the two walls are evenly stressed in the first bubble cycle. Through parameter analysis, we find that the jet directions of bubbles perform interesting discrepancies for different buoyancy and distances to walls. Some instructive conclusions are given to serve practical applications.展开更多
A digital photographic study of pool boiling with binary mixture Rll（CC13）-Rll3（CCl3CF3） was performed on a horizontal transparent heater at pressure of 0.1MPa. A high speed digital camera was applied to record th...A digital photographic study of pool boiling with binary mixture Rll（CC13）-Rll3（CCl3CF3） was performed on a horizontal transparent heater at pressure of 0.1MPa. A high speed digital camera was applied to record the bubble behaviors in boiling process. Strong effects of composition on bubble departure diameter, deparatre time, nucleation density were observed, which was attributed to the nature of the activation of the boiling surface and mass diffusion effects. The bubble departure diameter, departure period and nucleation density as functions of composition for binary mixtures R 11-R 113 were presented respectively. From the video images, it can be concluded that evaporation of microlayer is very important to the growth of bubble. It is also observed that there is not any liquid recruited into the microlayer below the bubble.展开更多
In order to design a sonochemical reactor with high reaction efficiency, it is important to clarify the size and intensity of the sonochemical reaction field. In this study, the reaction field in a sonochemical reacto...In order to design a sonochemical reactor with high reaction efficiency, it is important to clarify the size and intensity of the sonochemical reaction field. In this study, the reaction field in a sonochemical reactor is estimated from the distribution of pressure above the threshold for cavitation. The quantitation of hydroxide radical in a sonochemical reactor is obtained from the calculation of bubble dynamics and reaction equations. The distribution of the reaction field of the numerical simulation is consistent with that of the sonochemical luminescence. The sound absorption coefficient of liquid in the sonochemical reactor is much larger than that attributed to classical contributions which are heat conduction and shear viscosity. Under the dual irradiation, the reaction field becomes extensive and intensive because the acoustic pressure amplitude is intensified by the interference of two ultrasonic waves.展开更多
The bubble dynamic near a rigid wall with a wall jet was investigated by codynamics(CFD)method with the volume of fluid(VOF)model,which had been validated by vious experimental data.The effects of different velocities...The bubble dynamic near a rigid wall with a wall jet was investigated by codynamics(CFD)method with the volume of fluid(VOF)model,which had been validated by vious experimental data.The effects of different velocities of the wall jet and ditances on the bubble dynamics were studied.The results show that the bubble is squjet due to more force added on the bubble.When the velocity of the wall jet increa,the wall anthe pressure along the wall at collapse time increase because of the extra push indAs the stand-off distance increases,the pressure along the wall first increases then decrethe distance from the bubble to the wall increases.展开更多
Based on reported experimental data, a new model for single cavitation bubble dynamics is proposed considering a supercritical water （SCW） shell surrounding the bubble. Theoretical investigations show that the SCW s...Based on reported experimental data, a new model for single cavitation bubble dynamics is proposed considering a supercritical water （SCW） shell surrounding the bubble. Theoretical investigations show that the SCW shell apparently slows down the oscillation of the bubble and cools the gas temperature inside the collapsing bubble. Furthermore, the model is simplified to a Rayleigh-Plesset-like equation for a thin SCW shell. The dependence of the bubble dynamics on the thickness and density of the SCW shell is studied. The results show the bubble dynamics depends on the thickness but is insensitive to the density of the SCW shell. The thicker the SCW shell is, the smaller are the wall velocity and the gas temperature in the bubble. In the authors＇ opinion, the SCW shell works as a buffering agent. In collapsing, it is compressed to absorb a good deal of the work transformed into the bubble internal energy during bubble collapse so that it weakens the bubble oscillations.展开更多
The dynamic behavior of a cavitation bubble near an asymmetric hydrofoil is investigated experimentally through high-speed photography and theoretically using a Kelvin impulse model.The typical deformations arising du...The dynamic behavior of a cavitation bubble near an asymmetric hydrofoil is investigated experimentally through high-speed photography and theoretically using a Kelvin impulse model.The typical deformations arising during bubble collapse near the hydrofoil are analyzed qualitatively.The effects of the bubble position and the hydrofoil’s eccentricity angle are analyzed quantitatively.The spatial distribution of the Kelvin impulse near the hydrofoil are explored.Different morphological evolutions of a bubble near an asymmetric hydrofoil are revealed,with B-shaped,heart-shaped,and arc-shaped collapses.The velocity of the bubble interface close to the hydrofoil is significantly affected by the bubble-hydrofoil distance and the hydrofoil’s eccentricity angle,increasing as both the distance and the eccentricity angle grow.It is found that the Kelvin impulse sensitivity varies at different positions with respect to the asymmetric hydrofoil,being higher at the head and tail,and lower in the middle.展开更多
The hydrogen evolution reaction(HER)in electrochemical water splitting is crucial for green hydrogen production,yet its efficiency is limited by bubble dynamics at the electrode surface.Accumulated bubbles can block a...The hydrogen evolution reaction(HER)in electrochemical water splitting is crucial for green hydrogen production,yet its efficiency is limited by bubble dynamics at the electrode surface.Accumulated bubbles can block active sites,hinder mass transport,and increase local resistance,causing energy loss.Thus,precise bubble monitoring is crucial for understanding performance limitations and optimizing catalyst design.Conventional bubble monitoring techniques,such as optical microscopy,high-speed imaging,and electrochemical impedance,are constrained by real-time accuracy,complex post-processing,or signal interference at high current densities.Here,we present an in situ fiber optic sensing system that enables precise,real-time monitoring of bubble dynamics during HER.Unlike traditional methods,this system leverages the sensitivity and real-time capability of fiber optic sensors to quantify key parameters,such as growth rate,detachment rate,intake/output ratio,and detaching size.Its reliability and adaptability were validated using two different Pt/C-loaded carbon paper catalysts with distinct catalytic properties.Notably,the system also achieves a bubble detection limit of 79μm,which meets the spatial resolution requirements for monitoring bubble dynamics relevant to electrocatalytic activity in HER.This sensing platform establishes a practical framework for connecting interfacial gas evolution to electrochemical performance,offering valuable insight for optimizing HER efficiency through catalyst design.展开更多
We present a dynamic model of cavitation bubbles in a cluster,in which the effects of evaporation,condensation,and bubble-bubble interactions are taken into consideration.Under different ultrasound conditions,we exami...We present a dynamic model of cavitation bubbles in a cluster,in which the effects of evaporation,condensation,and bubble-bubble interactions are taken into consideration.Under different ultrasound conditions,we examine how the dynamics of cavitation bubbles are affected by several factors,such as the locations of the bubbles,the ambient radius,and the number of bubbles.Herein the variations of bubble radius,energy,temperature,pressure,and the quantity of vapor molecules are analyzed.Our findings reveal that bubble-bubble interactions can restrict the expansion of bubbles,reduce the exchange of energy among vapor molecules,and diminish the maximum internal temperature and pressure when bursting.The ambient radius of bubbles can influence the intensities of their oscillations,with clusters comprised of smaller bubbles creating optimal conditions for generating high-temperature and high-pressure regions.Moreover,an increase in the number of bubbles can further inhibit cavitation activities.The frequency,pressure and waveform of the driving wave can also exert a significant influence on cavitation activities,with rectangular waves enhancing and triangular waves weakening the cavitation of bubbles in the cluster.These results provide a theoretical basis for understanding the dynamics of cavitation bubbles in a bubble cluster,and the factors that affect their behaviors.展开更多
Condition monitoring and maintenance are essential for ensuring stable and reliable operation of facility transformer,reducing costs,and increasing expected life.Foam cannot be avoided within the power transformer whi...Condition monitoring and maintenance are essential for ensuring stable and reliable operation of facility transformer,reducing costs,and increasing expected life.Foam cannot be avoided within the power transformer which illustrates at least one of the principal roots of insulation deterioration.Due to the intricacy of the dynamics within the insulation system,involving bubble creation,migration,and accumulation,challenges arise in understanding these mechanisms.Consequently,the problems caused by bubble dynamics require further investigation.This paper provides a scientific review of issues related to bubble formation,migration,and dispersion and their electrical effects on power transformers.Various descriptions are given to highlight impact of the dynamics of the bubble within high voltage insulation fields,which covers bubble generation mechanism,and therefore,the quintessential influencing factors,state-ofthe-art advances in multi-physics coupled modeling of bubble dynamics,etc.Moreover,pending issues on bubble control and mitigation are addressed,as well as recommendations for future investigations.Nonetheless,this paper contains a useful quotation guide for researchers within an equivalent field of research,which can motivate readers to explore scientific solutions to prevailing bottleneck problems.展开更多
Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-t...Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional(quasi-2D)fluidized bed,including bubble equivalent diameter,bubble size distribution,average bubble density,bubble aspect ratio,bubble hold-up,bed expansion ratio,bubble radial position,and bubble velocity.The studies were performed by computational particle fluid dynamics(CPFD)numerical simulation and post-processed with digital image analysis(DIA)technique,at superficial gas velocities ranging from 2u_(mf) to 7u_(mf).The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds.However,it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution.The superficial gas velocity significantly affected the bubble equivalent diameter and evolution,while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles.Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity.Two core-annular flow structures could be found in the fluidized bed for all cases.The average bubble rising velocity increased with the increasing bubble equivalent diameter.For bubble lateral movement,the smaller bubbles might be more susceptible,and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles.The simulated results presented a valuable and novel approach for studying bubble dynamics properties.The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design,operation,and optimization of gas-solid fluidized bed reactors.展开更多
In this paper,the dynamic characteristics of the cylindrical bubbles under triple-frequency acoustic excitation are investigated theoretically.The analytical solution of the primary-superharmonic-subharmonic(PRI-SUPER...In this paper,the dynamic characteristics of the cylindrical bubbles under triple-frequency acoustic excitation are investigated theoretically.The analytical solution of the primary-superharmonic-subharmonic(PRI-SUPER-SUB)simultaneous resonance is obtained through the multi-scale method.Based on the analysis of the frequency response,the influencing mechanisms of the primary parameters(e.g.,the total amplitude,amplitude ratio,liquid viscosity,polytropic exponent,and bubble equilibrium radius)on the resonance are investigated quantitatively.The main conclusions include:(1)The solution for the simultaneous resonance of the cylindrical bubble exhibits jumping and hysteresis phenomena in the vicinity of the resonance frequency.(2)As the total amplitude,amplitude ratio,and equilibrium radius increase,the response amplitude of the PRI-SUPER-SUB simultaneous resonance increases,while the influence of the viscosity is the opposite.(3)The regions dominated by the instability of the simultaneous resonance is significantly affected by the system parameters.展开更多
Using the recently proposed bubble equation,we study the vibration characteristics of a bubble close to a solid boundary.The results indicate that a rigid boundary has an important effect on large-amplitude bubble vib...Using the recently proposed bubble equation,we study the vibration characteristics of a bubble close to a solid boundary.The results indicate that a rigid boundary has an important effect on large-amplitude bubble vibration.Whether the bubble vibration is stable or unstable strongly depends on the distance between the initial bubble center and the solid boundary.Furthermore,it also depends on both the amplitude and the frequency of the external perturbation.It is found that the smaller the distance between the initial bubble center and the solid boundary,the larger the initial bubble radius and the larger both the amplitude and frequency of the external perturbation,the more easily the bubble vibration becomes unstable.It is shown that this unstable bubble vibration is possibly related to the production of a reentrant microjet for the bubble,which suggests a potential method for estimating bubble size and the distance between the bubble center and the solid boundary by exerting an external perturbation with controllable amplitude and frequency on the liquid.Furthermore,the dependence of the natural frequency of the bubble on the external pressure for small-amplitude vibration can reveal the bubble radius and the distance between the bubble center and the solid boundary.In addition,the vibration characteristics of a bubble close to a solid boundary under a periodic external perturbation are revealed.Several bubble vibration modes are identified;the strongest vibration modes are those with the natural frequency and the external vibration frequency.展开更多
In this paper,the collapse dynamic properties of the cylindrical bubble near an arched cylinder bulge are researched relying on the conformal transformation and Kelvin impulse model.The properties of the liquid veloci...In this paper,the collapse dynamic properties of the cylindrical bubble near an arched cylinder bulge are researched relying on the conformal transformation and Kelvin impulse model.The properties of the liquid velocity distribution,Kelvin impulse distribution and the attraction zone of the jet are analyzed when the bubble and the bulge are arranged symmetrically and asymmetrically.The results show that,firstly,on the side of the bubble close to the bulge,there is a minimum collapse velocity of the bubble surface,which decreases as the bulge angle increases.In addition,the bulge’s effects on the Kelvin impulse strength and direction become larger as the bulge angle increases.When the bubble is incepted at the joint of the flat wall and the bulge,the impulse strength reaches its maximum.Finally,as the bulge angle increases from 45°–120°,the area of the jet attraction zone is gradually expanding,with its maximum width gradually increasing from 1.1–1.8 times the chord length of the bulge.展开更多
This paper aims to use the unified bubble dynamics equation to investigate bubble behavior in complex scenarios involving hybrid free surface/wall boundaries and interactions between multiple bubbles.The effect of sin...This paper aims to use the unified bubble dynamics equation to investigate bubble behavior in complex scenarios involving hybrid free surface/wall boundaries and interactions between multiple bubbles.The effect of singularity movement on the unified equation’s form is analyzed after deriving the bubble pulsation equation using a moving point source and a dipole,followed by discussions on the effect of migration compressibility-related terms on the bubble dynamics.In addition,the present study accounts for the impact of hybrid boundaries,including crossed and parallel boundaries,by introducing a finite number of mirror bubbles for the former and an infinite number of mirror bubbles for the latter.Spark bubble experiments and numerical simulation are conducted to validate the present theory.The application of the unified equation in multi-bubble interactions is exemplified by computing a spherical bubble array containing more than 100 uniformly distributed cavitation bubbles under different boundary conditions.The bubble cluster-induced pressure peak can reach nearly two times or even higher than that of an individual bubble,highlighting the damage potential caused by cavitation bubble clusters.展开更多
In this paper,the dynamic characteristics of the bubble in a broken confined domain are studied.The broken confined domain is composed of a solid wall and a plate that has a hole.The axisymmetric numerical model is es...In this paper,the dynamic characteristics of the bubble in a broken confined domain are studied.The broken confined domain is composed of a solid wall and a plate that has a hole.The axisymmetric numerical model is established by combining the Eulerian finite-element method with volume of fluid(VOF)method,and is validated by comparing the results with those from an experiment.Then the influences of the wall distance,plate distance and size of the hole are analyzed.The results show that cavity-attraction jet caused by the hole and annular jet caused by the upper solid wall compete with each other to dominate the bubble dynamics.The cavity-attraction jet develops earlier,but slower.Thus,jet load in the bubble stage is mainly generated by the annular jet with a higher impact speed.Within a certain range,the closer the hole is to the bubble or the smaller the hole,the longer the pulsation period of the bubble will be.展开更多
A tail bubble is generated behind a high-speed vehicle at the early stage of the underwater launch process.The tail bubble dynamic behavior involves expansion,overexpansion,contraction,pinch-off and jet formation,and ...A tail bubble is generated behind a high-speed vehicle at the early stage of the underwater launch process.The tail bubble dynamic behavior involves expansion,overexpansion,contraction,pinch-off and jet formation,and it significantly influences the vehicle’s movement.However,the tail bubble dynamic behavior is an issue not very well studied.This paper establishes a numerical model for the interaction between the tail bubble and the vehicle based on the boundary element method(BEM)to gain new insight into this issue.The BEM results are compared to a computational fluid dynamics model to validate the numerical model,and good agreement is achieved.Additionally,a convergence test of the BEM model is conducted to verify its independence of the mesh size.The influence of some governing parameters on the evolution of the tail bubble is then systematically studied,focusing on its maximum radius,pinch-off time,and pinch-off position.There are two pinch-off position regimes of the tail bubble,one at the bottom and the other near the middle.展开更多
In this paper,the dynamic behaviors of the cavitation bubble near a fixed spherical particle during the second oscillation period are analyzed based on the high-speed photographic system.The deformation and motion of ...In this paper,the dynamic behaviors of the cavitation bubble near a fixed spherical particle during the second oscillation period are analyzed based on the high-speed photographic system.The deformation and motion of the bubble during the second period are investigated by changing the distance between the particle and the bubble and the maximum radius of the bubble.Meanwhile,the variation of the equivalent radius and the centroid motions are analyzed,and the dynamic behaviors of the bubble are categorized according to the bubble morphological characteristics during the second period.Through this research,it is found that(1)The dynamic behaviors of the bubble during the second oscillation period could be divided into three typical cases:For case 1,a bulge would exist on the bubble interface away from the particle,and for case 2,a bulge would appear on the bubble interface and evolve towards the particle,while for case 3,the bubble would be divided into two parts.(2)The larger the dimensionless distance between the particle and the bubble,the smaller the maximum bubble equivalent radius in the second period,and the shorter the second oscillation period.(3)When the bubble is close to the particle,a counter-jet appears at the bubble interface away from the particle during the rebound stage.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52104321)the Natural Science Foundation of Chongqing,China(Grant No.CSTB2023NSCQ-MSX0871)the Science and Technology Research Program of Chongqing Municipal Education Commission(Grant No.KJQN202101404).
文摘Single argon bubble dynamics in liquid steel under Ruhrstahl-Heraeus(RH)vacuum conditions were simulated using the volume of fluid method,and the ideal gas law was used to consider bubble growth due to heat transfer and pressure drop.Additional simulation with a constant bubble density was also performed to validate the numerical method,and the predicted terminal bubble shape and velocity were found to agree with those presented in the Grace diagram and calculated by drag correlation,respectively.The simulation results under RH conditions indicate that the terminal bubble shape and velocity cannot be reached.The primary bubble growth occurs within a rising distance of 0.3 m owing to heating by the high-temperature liquid steel;subsequently,the bubble continues to grow under equilibrium with the hydrostatic pressure.When the initial diameter is 8-32 mm,the bubble diameter and rising velocity near the liquid surface are 80-200 mm and 0.5-0.8 m/s,respectively.The bubble rises rectilinearly with an axisymmetric shape,and the shape evolution history includes an initial sphere,(dimpled)ellipsoid,and spherical cap with satellite bubbles.
基金supported by National Natural Science Foundation of China(No.51807151)。
文摘In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating growth rather than a continuous expansion.Furthermore,a theoretical model and numerical calculation method were proposed,which revealed the dynamic mechanism of bubble growth.Good agreement between the theoretical results and experimental observations verified the general correctness and feasibility of the proposed method.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51709057 and 51979049)。
文摘This study is concerned with the dynamic characteristics of bubbles near two connected walls(one horizontal and the other inclined with an obtuse angle from the horizontal one). In this study, we set up an experiment system to conduct typical cases, and the boundary element method is employed to explain the bubble behavior and study the effect of relative parameters. Comparing the two mutually perpendicular walls, we find that the liquid jet deviates from the horizontal direction within a much shorter range. On the intersection of the two walls, the motions of bubbles have similar trends. The relatively low pressure between the bubble and walls causes the transition of the bubble, and a local high-pressure zone leads to the formation of a liquid jet. Moreover, there are moments when the two walls are evenly stressed in the first bubble cycle. Through parameter analysis, we find that the jet directions of bubbles perform interesting discrepancies for different buoyancy and distances to walls. Some instructive conclusions are given to serve practical applications.
基金Supported by the National Natural Science Foundation of China (No.10355001) and the Century Programme of ChineseAcademy of Sciences.
文摘A digital photographic study of pool boiling with binary mixture Rll（CC13）-Rll3（CCl3CF3） was performed on a horizontal transparent heater at pressure of 0.1MPa. A high speed digital camera was applied to record the bubble behaviors in boiling process. Strong effects of composition on bubble departure diameter, deparatre time, nucleation density were observed, which was attributed to the nature of the activation of the boiling surface and mass diffusion effects. The bubble departure diameter, departure period and nucleation density as functions of composition for binary mixtures R 11-R 113 were presented respectively. From the video images, it can be concluded that evaporation of microlayer is very important to the growth of bubble. It is also observed that there is not any liquid recruited into the microlayer below the bubble.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11404245,11204129,and 11211140039)
文摘In order to design a sonochemical reactor with high reaction efficiency, it is important to clarify the size and intensity of the sonochemical reaction field. In this study, the reaction field in a sonochemical reactor is estimated from the distribution of pressure above the threshold for cavitation. The quantitation of hydroxide radical in a sonochemical reactor is obtained from the calculation of bubble dynamics and reaction equations. The distribution of the reaction field of the numerical simulation is consistent with that of the sonochemical luminescence. The sound absorption coefficient of liquid in the sonochemical reactor is much larger than that attributed to classical contributions which are heat conduction and shear viscosity. Under the dual irradiation, the reaction field becomes extensive and intensive because the acoustic pressure amplitude is intensified by the interference of two ultrasonic waves.
基金National Natural Science Foundation of China(51422906,51609177)Key Projects in the National Science & Technology Pillar Program During the Twelfth Five-Year Plan Period(2012BAD08B03)
文摘The bubble dynamic near a rigid wall with a wall jet was investigated by codynamics(CFD)method with the volume of fluid(VOF)model,which had been validated by vious experimental data.The effects of different velocities of the wall jet and ditances on the bubble dynamics were studied.The results show that the bubble is squjet due to more force added on the bubble.When the velocity of the wall jet increa,the wall anthe pressure along the wall at collapse time increase because of the extra push indAs the stand-off distance increases,the pressure along the wall first increases then decrethe distance from the bubble to the wall increases.
基金supported by the National Natural Science Foundation of China(Grant Nos.11174145 and 11334005)
文摘Based on reported experimental data, a new model for single cavitation bubble dynamics is proposed considering a supercritical water （SCW） shell surrounding the bubble. Theoretical investigations show that the SCW shell apparently slows down the oscillation of the bubble and cools the gas temperature inside the collapsing bubble. Furthermore, the model is simplified to a Rayleigh-Plesset-like equation for a thin SCW shell. The dependence of the bubble dynamics on the thickness and density of the SCW shell is studied. The results show the bubble dynamics depends on the thickness but is insensitive to the density of the SCW shell. The thicker the SCW shell is, the smaller are the wall velocity and the gas temperature in the bubble. In the authors＇ opinion, the SCW shell works as a buffering agent. In collapsing, it is compressed to absorb a good deal of the work transformed into the bubble internal energy during bubble collapse so that it weakens the bubble oscillations.
基金supported by the National Natural Science Foundation of China(Project No.51976056).
文摘The dynamic behavior of a cavitation bubble near an asymmetric hydrofoil is investigated experimentally through high-speed photography and theoretically using a Kelvin impulse model.The typical deformations arising during bubble collapse near the hydrofoil are analyzed qualitatively.The effects of the bubble position and the hydrofoil’s eccentricity angle are analyzed quantitatively.The spatial distribution of the Kelvin impulse near the hydrofoil are explored.Different morphological evolutions of a bubble near an asymmetric hydrofoil are revealed,with B-shaped,heart-shaped,and arc-shaped collapses.The velocity of the bubble interface close to the hydrofoil is significantly affected by the bubble-hydrofoil distance and the hydrofoil’s eccentricity angle,increasing as both the distance and the eccentricity angle grow.It is found that the Kelvin impulse sensitivity varies at different positions with respect to the asymmetric hydrofoil,being higher at the head and tail,and lower in the middle.
基金supported by the following:the National Natural Science Foundation of China(Nos.62405141 and 22479079)Natural Science Research Start-up Foundation of Recruiting Talents of Nanjing University of Posts and Telecommunications(No.NY222178).
文摘The hydrogen evolution reaction(HER)in electrochemical water splitting is crucial for green hydrogen production,yet its efficiency is limited by bubble dynamics at the electrode surface.Accumulated bubbles can block active sites,hinder mass transport,and increase local resistance,causing energy loss.Thus,precise bubble monitoring is crucial for understanding performance limitations and optimizing catalyst design.Conventional bubble monitoring techniques,such as optical microscopy,high-speed imaging,and electrochemical impedance,are constrained by real-time accuracy,complex post-processing,or signal interference at high current densities.Here,we present an in situ fiber optic sensing system that enables precise,real-time monitoring of bubble dynamics during HER.Unlike traditional methods,this system leverages the sensitivity and real-time capability of fiber optic sensors to quantify key parameters,such as growth rate,detachment rate,intake/output ratio,and detaching size.Its reliability and adaptability were validated using two different Pt/C-loaded carbon paper catalysts with distinct catalytic properties.Notably,the system also achieves a bubble detection limit of 79μm,which meets the spatial resolution requirements for monitoring bubble dynamics relevant to electrocatalytic activity in HER.This sensing platform establishes a practical framework for connecting interfacial gas evolution to electrochemical performance,offering valuable insight for optimizing HER efficiency through catalyst design.
基金Project supported by the National Natural Science Foundation of China (Grant No.12074354)。
文摘We present a dynamic model of cavitation bubbles in a cluster,in which the effects of evaporation,condensation,and bubble-bubble interactions are taken into consideration.Under different ultrasound conditions,we examine how the dynamics of cavitation bubbles are affected by several factors,such as the locations of the bubbles,the ambient radius,and the number of bubbles.Herein the variations of bubble radius,energy,temperature,pressure,and the quantity of vapor molecules are analyzed.Our findings reveal that bubble-bubble interactions can restrict the expansion of bubbles,reduce the exchange of energy among vapor molecules,and diminish the maximum internal temperature and pressure when bursting.The ambient radius of bubbles can influence the intensities of their oscillations,with clusters comprised of smaller bubbles creating optimal conditions for generating high-temperature and high-pressure regions.Moreover,an increase in the number of bubbles can further inhibit cavitation activities.The frequency,pressure and waveform of the driving wave can also exert a significant influence on cavitation activities,with rectangular waves enhancing and triangular waves weakening the cavitation of bubbles in the cluster.These results provide a theoretical basis for understanding the dynamics of cavitation bubbles in a bubble cluster,and the factors that affect their behaviors.
基金supported in part by the Science and Technology Project of SGCC:Research on bubble generation mechanism and behavior characteristics of oil-immersed power transformer/high-voltage reactor under the coupling action of vibration and electric field(No.52120520001A).
文摘Condition monitoring and maintenance are essential for ensuring stable and reliable operation of facility transformer,reducing costs,and increasing expected life.Foam cannot be avoided within the power transformer which illustrates at least one of the principal roots of insulation deterioration.Due to the intricacy of the dynamics within the insulation system,involving bubble creation,migration,and accumulation,challenges arise in understanding these mechanisms.Consequently,the problems caused by bubble dynamics require further investigation.This paper provides a scientific review of issues related to bubble formation,migration,and dispersion and their electrical effects on power transformers.Various descriptions are given to highlight impact of the dynamics of the bubble within high voltage insulation fields,which covers bubble generation mechanism,and therefore,the quintessential influencing factors,state-ofthe-art advances in multi-physics coupled modeling of bubble dynamics,etc.Moreover,pending issues on bubble control and mitigation are addressed,as well as recommendations for future investigations.Nonetheless,this paper contains a useful quotation guide for researchers within an equivalent field of research,which can motivate readers to explore scientific solutions to prevailing bottleneck problems.
基金the financial support provided by National Key R&D Project of China(grant No.2020YFB0606303)the technical supports received from Sam Clark in CPFD Software,LLC of USA,and from Hi-Key Technology Incorporated of China.
文摘Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional(quasi-2D)fluidized bed,including bubble equivalent diameter,bubble size distribution,average bubble density,bubble aspect ratio,bubble hold-up,bed expansion ratio,bubble radial position,and bubble velocity.The studies were performed by computational particle fluid dynamics(CPFD)numerical simulation and post-processed with digital image analysis(DIA)technique,at superficial gas velocities ranging from 2u_(mf) to 7u_(mf).The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds.However,it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution.The superficial gas velocity significantly affected the bubble equivalent diameter and evolution,while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles.Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity.Two core-annular flow structures could be found in the fluidized bed for all cases.The average bubble rising velocity increased with the increasing bubble equivalent diameter.For bubble lateral movement,the smaller bubbles might be more susceptible,and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles.The simulated results presented a valuable and novel approach for studying bubble dynamics properties.The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design,operation,and optimization of gas-solid fluidized bed reactors.
基金supported by the National Natural Science Foundation of China(Grant No.51976056).
文摘In this paper,the dynamic characteristics of the cylindrical bubbles under triple-frequency acoustic excitation are investigated theoretically.The analytical solution of the primary-superharmonic-subharmonic(PRI-SUPER-SUB)simultaneous resonance is obtained through the multi-scale method.Based on the analysis of the frequency response,the influencing mechanisms of the primary parameters(e.g.,the total amplitude,amplitude ratio,liquid viscosity,polytropic exponent,and bubble equilibrium radius)on the resonance are investigated quantitatively.The main conclusions include:(1)The solution for the simultaneous resonance of the cylindrical bubble exhibits jumping and hysteresis phenomena in the vicinity of the resonance frequency.(2)As the total amplitude,amplitude ratio,and equilibrium radius increase,the response amplitude of the PRI-SUPER-SUB simultaneous resonance increases,while the influence of the viscosity is the opposite.(3)The regions dominated by the instability of the simultaneous resonance is significantly affected by the system parameters.
基金supported by the National Natural Science Foundation of China(Grant No.12275223).
文摘Using the recently proposed bubble equation,we study the vibration characteristics of a bubble close to a solid boundary.The results indicate that a rigid boundary has an important effect on large-amplitude bubble vibration.Whether the bubble vibration is stable or unstable strongly depends on the distance between the initial bubble center and the solid boundary.Furthermore,it also depends on both the amplitude and the frequency of the external perturbation.It is found that the smaller the distance between the initial bubble center and the solid boundary,the larger the initial bubble radius and the larger both the amplitude and frequency of the external perturbation,the more easily the bubble vibration becomes unstable.It is shown that this unstable bubble vibration is possibly related to the production of a reentrant microjet for the bubble,which suggests a potential method for estimating bubble size and the distance between the bubble center and the solid boundary by exerting an external perturbation with controllable amplitude and frequency on the liquid.Furthermore,the dependence of the natural frequency of the bubble on the external pressure for small-amplitude vibration can reveal the bubble radius and the distance between the bubble center and the solid boundary.In addition,the vibration characteristics of a bubble close to a solid boundary under a periodic external perturbation are revealed.Several bubble vibration modes are identified;the strongest vibration modes are those with the natural frequency and the external vibration frequency.
基金financially supported by the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20240466).
文摘In this paper,the collapse dynamic properties of the cylindrical bubble near an arched cylinder bulge are researched relying on the conformal transformation and Kelvin impulse model.The properties of the liquid velocity distribution,Kelvin impulse distribution and the attraction zone of the jet are analyzed when the bubble and the bulge are arranged symmetrically and asymmetrically.The results show that,firstly,on the side of the bubble close to the bulge,there is a minimum collapse velocity of the bubble surface,which decreases as the bulge angle increases.In addition,the bulge’s effects on the Kelvin impulse strength and direction become larger as the bulge angle increases.When the bubble is incepted at the joint of the flat wall and the bulge,the impulse strength reaches its maximum.Finally,as the bulge angle increases from 45°–120°,the area of the jet attraction zone is gradually expanding,with its maximum width gradually increasing from 1.1–1.8 times the chord length of the bulge.
基金supported by the National Natural Science Foundation of China(Grant Nos.52088102,and 51925904)the National Key R&D Program of China(Grant Nos.2022YFC2803500,and 2018YFC0308900)+1 种基金the Finance Science and Technology Project of Hainan Province(Grant No.ZDKJ2021020)the Xplore Prize。
文摘This paper aims to use the unified bubble dynamics equation to investigate bubble behavior in complex scenarios involving hybrid free surface/wall boundaries and interactions between multiple bubbles.The effect of singularity movement on the unified equation’s form is analyzed after deriving the bubble pulsation equation using a moving point source and a dipole,followed by discussions on the effect of migration compressibility-related terms on the bubble dynamics.In addition,the present study accounts for the impact of hybrid boundaries,including crossed and parallel boundaries,by introducing a finite number of mirror bubbles for the former and an infinite number of mirror bubbles for the latter.Spark bubble experiments and numerical simulation are conducted to validate the present theory.The application of the unified equation in multi-bubble interactions is exemplified by computing a spherical bubble array containing more than 100 uniformly distributed cavitation bubbles under different boundary conditions.The bubble cluster-induced pressure peak can reach nearly two times or even higher than that of an individual bubble,highlighting the damage potential caused by cavitation bubble clusters.
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFC0308900)the National Natural Science Foundation of China(Grant Nos.51879050,51925904).
文摘In this paper,the dynamic characteristics of the bubble in a broken confined domain are studied.The broken confined domain is composed of a solid wall and a plate that has a hole.The axisymmetric numerical model is established by combining the Eulerian finite-element method with volume of fluid(VOF)method,and is validated by comparing the results with those from an experiment.Then the influences of the wall distance,plate distance and size of the hole are analyzed.The results show that cavity-attraction jet caused by the hole and annular jet caused by the upper solid wall compete with each other to dominate the bubble dynamics.The cavity-attraction jet develops earlier,but slower.Thus,jet load in the bubble stage is mainly generated by the annular jet with a higher impact speed.Within a certain range,the closer the hole is to the bubble or the smaller the hole,the longer the pulsation period of the bubble will be.
基金Project supported by the National Natural Science Foundation of China(Grant No.U20B2005).
文摘A tail bubble is generated behind a high-speed vehicle at the early stage of the underwater launch process.The tail bubble dynamic behavior involves expansion,overexpansion,contraction,pinch-off and jet formation,and it significantly influences the vehicle’s movement.However,the tail bubble dynamic behavior is an issue not very well studied.This paper establishes a numerical model for the interaction between the tail bubble and the vehicle based on the boundary element method(BEM)to gain new insight into this issue.The BEM results are compared to a computational fluid dynamics model to validate the numerical model,and good agreement is achieved.Additionally,a convergence test of the BEM model is conducted to verify its independence of the mesh size.The influence of some governing parameters on the evolution of the tail bubble is then systematically studied,focusing on its maximum radius,pinch-off time,and pinch-off position.There are two pinch-off position regimes of the tail bubble,one at the bottom and the other near the middle.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51976056,52076215).
文摘In this paper,the dynamic behaviors of the cavitation bubble near a fixed spherical particle during the second oscillation period are analyzed based on the high-speed photographic system.The deformation and motion of the bubble during the second period are investigated by changing the distance between the particle and the bubble and the maximum radius of the bubble.Meanwhile,the variation of the equivalent radius and the centroid motions are analyzed,and the dynamic behaviors of the bubble are categorized according to the bubble morphological characteristics during the second period.Through this research,it is found that(1)The dynamic behaviors of the bubble during the second oscillation period could be divided into three typical cases:For case 1,a bulge would exist on the bubble interface away from the particle,and for case 2,a bulge would appear on the bubble interface and evolve towards the particle,while for case 3,the bubble would be divided into two parts.(2)The larger the dimensionless distance between the particle and the bubble,the smaller the maximum bubble equivalent radius in the second period,and the shorter the second oscillation period.(3)When the bubble is close to the particle,a counter-jet appears at the bubble interface away from the particle during the rebound stage.
