Experiments were conducted to investigate the dynamics of an oscillating bubble generated by a spark in the presence of an inclined attached air bubble.The study primarily focused on the influence of the inclination a...Experiments were conducted to investigate the dynamics of an oscillating bubble generated by a spark in the presence of an inclined attached air bubble.The study primarily focused on the influence of the inclination angle on the behavior of bubble jetting orientation,air bubble shape modes,and motion characteristics of the interaction between the two bubbles.Various complex bubble jetting behaviors were observed,including the presence of multiple types of bubble jetting directions,bubble splitting,and multidirectional jets.Four types of air bubble shapes were defined,namely inclined cup cover-shaped(with and without splitting),double-peaked cup cover-shaped,and inclined L-shaped air bubbles.The formation of different types of bubble jets was analyzed using the vector synthesis principle of the Bjerknes force exerted by the inclined attached air bubble and a steel plate.To describe the diverse orientations of bubble jetting and air bubble shapes,new parameters namely the dimensionless spark bubble oscillation time T^(*)and volume ratio V^(*)that consider the inclination angle are proposed.The findings of this investigation contribute to the existing knowledge and have the potential to further enhance methods for mitigating cavitation damage in marine,hydraulic machinery systems,and medical fields.l fields.展开更多
Numerical simulations of the non-spherical evolution of a pulsating bubble interacting with a stationary air bubble attached to a fixed structure were performed using a three-dimensional boundary integral method by im...Numerical simulations of the non-spherical evolution of a pulsating bubble interacting with a stationary air bubble attached to a fixed structure were performed using a three-dimensional boundary integral method by implementing the mirror image method to simplify the processing of the numerical model. Code validation was accomplished by comparing the numerical results with the laboratory experimental data obtained in our previous study. Complex phenomena were observed, including three types of bubble jet forms, which depended strongly on the distance parameter with respect to the initial location of the bubble from the plate, the bubble strength parameter and the initial air bubble radius parameters. The results of the simulations provide detail insight into interesting bubble jetting phenomena,such as bubble splitting, jets moving away from the plate, and bubble shedding. The dimensionless distance parameter and the initial air bubble radius parameter play a major role in determining the shapes of two bubbles and the jetting direction. The air bubble strength parameter did not change the bubble jet direction but influenced the bubble shape.The detachment of the attached air bubble under oscillating bubble suction was easily observed for a small initial air bubble. These results showed that bubble jetting toward the plate was manipulated through the effect of attached air bubble, and that cavitation-based applications and underwater explosion bubble may benefit from this erosion mitigation approach.展开更多
Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow...Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.展开更多
AIM:To introduce a new surgical technique,air-bubble technique for the management of posterior capsule rupture(PCR)and to evaluate the safety and efficacy of the technique.METHODS:A retrospective case series analysis ...AIM:To introduce a new surgical technique,air-bubble technique for the management of posterior capsule rupture(PCR)and to evaluate the safety and efficacy of the technique.METHODS:A retrospective case series analysis of 24 eyes of 24 patients,in which the air bubble technique was used for the management of PCR,was performed.Once PCR occurred,a dispersive ophthalmic viscosurgical device(OVD)was injected into the tear.And small volumes(0.2-0.3 mL)of air bubbles were injected beneath the OVD.The air bubble served as a physical barrier and supported the posterior capsule.RESULTS:After surgery,none of the patients had serious complications during the follow-up period of 1 y.Extension of the PCR size occurred in only 2 cases,and additional OVD injection was required only in 3 cases.Air bubbles imparted great stability to the nuclear pieces and the posterior capsule.CONCLUSION:The air-bubble technique may be considered a safe and effective procedure for managing a PCR.It may be of value to the inexperienced cataract surgeon.展开更多
Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined ...Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D b < 66 mm and 40 mm < D b < 69 mm with the magnetite powder of 0.3 mm+0.15mm and 0.15mm+0.074mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1mm fine coal as medium solids were utilized to carry out the separation experiment on 6-50mm raw coal. The results show that an optimal separation density d P of 1.73g/cm 3 with a probable error E of 0.07g/cm 3 and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.展开更多
We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are parti...We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are particularly investigated in various cases for distinguishing efficiently the acoustic localisation from the effects of acoustic absorption caused by the viscosity of medium. The numerical results reveal the phenomenon of 'phase transition' characterized by an unusual collective oscillation of bubbles, which is an effective criterion to unambiguously identify the acoustic localisation in the presence of viscosity. Within the localisation region, the phenomenon of phase transition persists, and a remarkable decrease in the fluctuation of the oscillation phases of bubbles is observed. The localisation phenomenon will be impaired by the enhancement of the viscosity factors, and the extent to which the acoustic wave is localised may be determined by appropriately analyzing the values of the oscillation phases or the amount of reduction of the phase fluctuation. The results are particularly significant for the practical experiments in an attempt to observe the acoustic localisation in such a medium, which is in general subjected to the interference of the great ambiguity resulting from the effect of acoustic absorption.展开更多
In this paper, a series of experiments were carried out on the air concentration distribution. In the cavity zone, the air bubble frequency distribution was similar to the air concentration distribution. The air bubbl...In this paper, a series of experiments were carried out on the air concentration distribution. In the cavity zone, the air bubble frequency distribution was similar to the air concentration distribution. The air bubble frequency increased from the bottom and then decreased near the tmaerated black water region. The position of the maximum air bubble frequencyfmax moved downwards. At the air-water cross section, the relationship between the air bubble frequency and the air concentration was self-similar, the position of the maximum air bubble frequency caused by the air-water discontinuity gradually approached C = 0.50 with the development of aeration. Meanwhile, the dimensionless air bubble frequency in the cavity zone followed a parabolic function.展开更多
Theδ18O of ice core enclosed gaseous oxygen(δ18Obub)has been widely used for climate reconstruction in polar regions.Yet,less is known about its climatic implication in the mountainous glaciers as the lack of contin...Theδ18O of ice core enclosed gaseous oxygen(δ18Obub)has been widely used for climate reconstruction in polar regions.Yet,less is known about its climatic implication in the mountainous glaciers as the lack of continuous record.Here,we present a long-term,continuousδ18Obub record from the Tanggula glacier in the central Tibetan Plateau(TP).Based on comparisons of its variation with regional climate and glacier changes,we found that there was a good correlation between the variation of theδ18Obub in this alpine ice core and the accumulation and melting of this glacier.The more developed the firn layer on glacier surface,the more positive theδ18Obub.Conversely,the more intense the glacier melting,the more negative theδ18Obub.Combined with the chronology of ice core enclosed gases,the glacier variations since the late Holocene in the central TP were reconstructed.The result showed that there were four accumulation and three deficit periods of glaciers in this region.The strongest glacier accumulation period was 1610-300 B.C.,which corresponds to the Neoglaciation.The most significant melting period was the last 100 years,which corresponds to the recent global warming.The Medieval Warm Period was relatively significant in the central TP.However,during the Little Ice Age,there was no significant glacier accumulation in the central TP,and even short deficit events occurred.Comparisons of the late Holocene glacier variation in the central TP with glacier and climate variations in the TP and the Northern Hemisphere showed that it was closely related to the North Atlantic Oscillation.展开更多
Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and...Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements.The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness.The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning.Maximum adhesion forces between water and surfaces were 111.70,125.48,and 136.42μN when the roughness was 0.23,0.98,and 2.79 μm,respectively.In contrast,under a liquid environment,the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water.Maximum adhesion forces of increasing roughness were 97.14,42.76,and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48,145.84,and 121.02 lN between oil droplet and surfaces,respectively.Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.展开更多
The sudden transition from a high-velocity, supercritical open channel flow into a slow-moving sub-critical flow is a hydraulic jump. Such a flow is characterised by a sudden rise of the free-surface, with some strong...The sudden transition from a high-velocity, supercritical open channel flow into a slow-moving sub-critical flow is a hydraulic jump. Such a flow is characterised by a sudden rise of the free-surface, with some strong energy dissipation and air entrainment, waves and spray. New two-phase flow measurements were performed in the developing flow region using a large-size facility operating at large Reynolds numbers. The experimental results demonstrated the complexity of the flow with a developing mixing layer in which entrained bubbles are advected in a high shear stress flow. The relationship between bubble count rates and void fractions was non-unique in the shear zone, supporting earlier observations of some form of double diffusion process between momentum and air bubbles. In the upper region, the flow consisted primarily of water drops and packets sur-rounded by air. Visually significant pray and splashing were significant above the jump roller. The present study is the first com-prehensive study detailing the two-phase flow properties of both the bubbly and spray regions of hydraulic jumps, a first step towards understanding the interactions between bubble entrainment and droplet ejection processes.展开更多
A high-resolution 2ooo-year methane record has been constructed from an ice core recovered at 7200 m a.s.1, on the Dasuopu Glacier in the central Himalayas. This sub-tropical methane record reveals an increasing trend...A high-resolution 2ooo-year methane record has been constructed from an ice core recovered at 7200 m a.s.1, on the Dasuopu Glacier in the central Himalayas. This sub-tropical methane record reveals an increasing trend in the concentration of methane during the industrial era that is similar to observations from polar regions. However, we also observed the differences in the atmospheric methane mixing ratio between this monsoon record and those from polar regions during pre-industrial times. In the time interval o N 1850 A.D., the average methane concentration in the Dasuopu ice core was 782±40 ppbv and the maximum temporal variation exceeded 200 ppbv. The difference gradient of methane concentration in Dasuopu ice core with Greenland and Antarctica cores are 66±40 ppbv and 107±40 ppbv, respectively. This suggests that the tropical latitudes might have acted as a major global methane source in preindustrial times. In addition, the temporal fluctuation of the pre-industrial methane records suggests that monsoon evolution incorporated with high methane emission from south Asia might be responsible for the relatively high methane concentration observed in the Dasuopu ice core around A.D. 800 and A.D. 1600. These results provide a rough understanding of the contribution of tropical methane source to the global methane budget and also the relationship betweenatmospheric methane and climate change.展开更多
On the basis of the mineralizing mechanism of froth cyclone, this paper expounds that the froth cyclone flotation process is accomplished in a limited centrifugal field. The main feature of air bubble mineralizing in ...On the basis of the mineralizing mechanism of froth cyclone, this paper expounds that the froth cyclone flotation process is accomplished in a limited centrifugal field. The main feature of air bubble mineralizing in the froth cyclone is a synthetic mineralizing process, of which the non collision mineralization of minute air bubble separated out dominates, supplemented with the collision mineralization. Moreover, this paper points out that the hydrophobic separated out and centrifugal force strengthen the selectivity of fine coal particle, accelerate the flotation speed and improve the slime recovery.展开更多
Cavitation in plants is caused by development of air bubbles, which is related to their equilibrium and development. There is a univariate cubic equation for bubble balance. New root formula of this kind of equation w...Cavitation in plants is caused by development of air bubbles, which is related to their equilibrium and development. There is a univariate cubic equation for bubble balance. New root formula of this kind of equation was proposed by Shenjin Fan, which is simpler than the Caldan’s. Using Shenjin formulas and taking water pressure <em>P</em><sub>1</sub> as an independent variable, this paper gives the exact solution of the equation under certain conditions. The stability of the equilibrium of an air bubble in its different radius ranges is obtained by the way different from the previous. This kind of cavitation includes two types: First type may be caused by the growth of pre-existent air bubbles;Second type is air seeding, here defined as the sucking of air bubbles from already gas-filled conduits. For air seeding three ways of cavitation have been proposed. For the first type this paper puts forward that two ways of cavitation can occur, which are the same with the first two ways of air seeding except of air reservoirs. Moreover, for the first way of the first type, the range of water pressures is the same with that of the first way of air seeding. For the second way of the first type the range of water pressures is much wider, or the pressure range equals the pressure sum of the second and third ways of air seeding. Through the specific data the relationship between the two types is given.展开更多
Although hydraulic drives have an advantage of high power density, volumetric shrinkage of hydraulic fluids due to pressure causes various disadvantages such as delay of hydraulic response and compression energy loss....Although hydraulic drives have an advantage of high power density, volumetric shrinkage of hydraulic fluids due to pressure causes various disadvantages such as delay of hydraulic response and compression energy loss. Hydraulic fluids of new concept, high bulk modulus oils, have been developed as a new approach to improve the performance of a hydraulic servo system and verified. In this paper, practical performances of high bulk modulus oil, such as oil temperature rise during pump test, air bubbles generation by ultrasonic wave vibration, oxidation stability and anti-wear property, were studied. And the new oil was confirmed to have excellent practical performances besides advantages in pressure response and volumetric efficiency of pumps. Various new applications of the new oil are promising.展开更多
The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical c...The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction.The bubble-bubble interaction can be considered in two different conditions.The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small,and away from the air bubble if the air bubble is relatively large.The two zones are identified in the bubble-boundary interaction,and they are the danger zone and the safety zone.The relative position,the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction,which can be considered in several conditions according to the responses of the bubbles.Air jets are found to penetrate into the cavitation bubbles.The cavitation bubble and the air bubble(air jet) move in their own way without mixing.The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary.The influence of the air bubble and the influence of the boundary may be combined,like some thing of a vector.展开更多
Experiments are carried out by using high-speed photography to investigate the interaction between the spark-generated cavitation bubble and the air bubble in its surrounding fluid. Three problems are discussed in det...Experiments are carried out by using high-speed photography to investigate the interaction between the spark-generated cavitation bubble and the air bubble in its surrounding fluid. Three problems are discussed in detail: the impact of the air bubble upon the development of the cavitation bubble, the evolution of the air bubble under the influence of the cavitation bubble, and the change of the fluid pressure during the development of a micro jet of the cavitation bubble. Based on the experimental results, under the condition of no air bubble present, the lifetime of the cavitation bubble from expansion to contraction increases with the increase of the maximum radius. On the other hand, when there is an air bubble present, different sized cavitation bubbles have similarity with one another generally in terms of the lifetime from expansion to contraction, which does not depend on the maximum radius. Also, with the presence of an air bubble, the lifetime of the smaller cavitation bubble is extended while that of the bigger ones reduced. Furthermore, it is shown in the experiment that the low pressure formed in the opposite direction to the cavitation bubble micro jet makes the air bubble in the low pressure area being stretched into a steplike shape.展开更多
Over the past 60 years, the air concentration in water has been considered as a control index of cavitation erosion reduction and widely used in the designs of hydraulic structures. However, the mechanism of air entra...Over the past 60 years, the air concentration in water has been considered as a control index of cavitation erosion reduction and widely used in the designs of hydraulic structures. However, the mechanism of air entrainment against cavitation erosion has been paid good attention to. In the present work, the effect of air bubble size on cavitation erosion reduction was experimentally investigated. A device with micron-scale orifice diameters(10, 20 and 50 μm in size) was specially designed to introduce air bubbles into water. The experiments about the effect of air bubble size were conducted by means of a vibratory apparatus, including the behavior of formation and movement for single air bubble, the characteristics of cavitation erosion reduction at different air entrainment conditions. The findings demonstrate that high air concentration has significant effects on cavitation erosion reduction.But, a notable problem was that the size of air bubbles is of outstanding effect on cavitation erosion reduction. Small air bubbles support to alleviate cavitation erosion, even at same air concentration.展开更多
The wave dissipating performance of air bubble breakwaters with different layouts is studied by experimental and numerical methods in this article. Based on the assumpation that the mixture of air and water is regarde...The wave dissipating performance of air bubble breakwaters with different layouts is studied by experimental and numerical methods in this article. Based on the assumpation that the mixture of air and water is regarded as a variable density fluid, the mathematical model of the air bubble breakwater is built. The numerical simulation results are compared with the experimental data, which shows that the mathematical model is reasonable for the transmission coefficient Ct m. The influencing factors are studied experimentally and numerically, including the incident wave height H i, the incidentt wave period T , the air amount Qm , the submerged pipe depth D and the single or double air discharging pipe structure. Some valuable conclusions are obtained for further research of the mechanism and practical applications of air bubble breakwaters.展开更多
The cavitation erosion is one of the common damage modes in water engineering.The study of the interaction among cavitation bubbles,air bubbles and the wall is of great significance for understanding the mechanism of ...The cavitation erosion is one of the common damage modes in water engineering.The study of the interaction among cavitation bubbles,air bubbles and the wall is of great significance for understanding the mechanism of the air entrainment to alleviate the cavitation and to enhance the cavitation erosion mitigation effect of aeration.By using the high-speed camera,the regular patterns of the collapse of cavitation bubbles in the vicinity of the wall and the air bubbles are studied in this paper.It is shown that in the vicinity of air bubbles,the cavitation bubbles may only collapse towards or from air bubbles,while under the dual impacts of air bubbles and the wall,the direction of collapse of the cavitation bubbles depends on the combined vector of the impact forces of the air bubbles and the wall.When the air bubbles are very close to the cavitation bubbles,the air bubbles will be penetrated and stretched by the cavitation bubbles,when the distance between them is short enough,the cavitation bubbles and the air bubbles will connect to form gas-type cavitation bubbles,and the collapse strength will be significantly decreased,when there are two air bubbles near the cavitation bubbles,they may even be penetrated successively by the cavitation bubbles.Thus it can be concluded that during the air entrainment to alleviate the cavitation,the number of air bubbles is more important than the total air concentration.展开更多
A novel, functionalized bubble surface can be obtained in dissolved air flotation (DAF) by dosing chemicals in the saturator. In this study, different cationic chemicals were used as bubble surface modifiers, and th...A novel, functionalized bubble surface can be obtained in dissolved air flotation (DAF) by dosing chemicals in the saturator. In this study, different cationic chemicals were used as bubble surface modifiers, and their effects on natural organic matter (NOM) removal from river water were investigated. NOM in the samples was fractionated based on molecular weight and hydrophobicity. The disinfection byproduct formation potentials of each fraction and their removal efficiencies were also evaluated. The results showed that chitosan was the most promising bubble modifier compared with a surfactant and a synthetic polymer. Tiny bubbles in the OAF pump system facilitated the adsorption of chitosan onto microbubble surfaces. The hydrophobic NOM fraction was preferentially removed by chitosan-modified bubbles. Decreasing the recycle water pH from 7.0 to 5.5 improved the removal of hydrophilic NOM with low molecular weight. Likewise, hydrophilic organic compounds gave high dihaloacetic acid yields in raw water. An enhanced reduction of haloacetic acid precursors was obtained with recycle water at pH values of 5.5 and 4.0. The experimental results indicate that NOM fractions may interact with bubbles through different mechanisms. Positive bubble modification provides an alternative approach for OAF to enhance NOM removal.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52171311,52271279)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.20KJB510046)。
文摘Experiments were conducted to investigate the dynamics of an oscillating bubble generated by a spark in the presence of an inclined attached air bubble.The study primarily focused on the influence of the inclination angle on the behavior of bubble jetting orientation,air bubble shape modes,and motion characteristics of the interaction between the two bubbles.Various complex bubble jetting behaviors were observed,including the presence of multiple types of bubble jetting directions,bubble splitting,and multidirectional jets.Four types of air bubble shapes were defined,namely inclined cup cover-shaped(with and without splitting),double-peaked cup cover-shaped,and inclined L-shaped air bubbles.The formation of different types of bubble jets was analyzed using the vector synthesis principle of the Bjerknes force exerted by the inclined attached air bubble and a steel plate.To describe the diverse orientations of bubble jetting and air bubble shapes,new parameters namely the dimensionless spark bubble oscillation time T^(*)and volume ratio V^(*)that consider the inclination angle are proposed.The findings of this investigation contribute to the existing knowledge and have the potential to further enhance methods for mitigating cavitation damage in marine,hydraulic machinery systems,and medical fields.l fields.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 52171311 and 52271279)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 20KJB510046)。
文摘Numerical simulations of the non-spherical evolution of a pulsating bubble interacting with a stationary air bubble attached to a fixed structure were performed using a three-dimensional boundary integral method by implementing the mirror image method to simplify the processing of the numerical model. Code validation was accomplished by comparing the numerical results with the laboratory experimental data obtained in our previous study. Complex phenomena were observed, including three types of bubble jet forms, which depended strongly on the distance parameter with respect to the initial location of the bubble from the plate, the bubble strength parameter and the initial air bubble radius parameters. The results of the simulations provide detail insight into interesting bubble jetting phenomena,such as bubble splitting, jets moving away from the plate, and bubble shedding. The dimensionless distance parameter and the initial air bubble radius parameter play a major role in determining the shapes of two bubbles and the jetting direction. The air bubble strength parameter did not change the bubble jet direction but influenced the bubble shape.The detachment of the attached air bubble under oscillating bubble suction was easily observed for a small initial air bubble. These results showed that bubble jetting toward the plate was manipulated through the effect of attached air bubble, and that cavitation-based applications and underwater explosion bubble may benefit from this erosion mitigation approach.
基金financially supported by the National Key Research and Development Program of China(Grant No.2016YFC0401901)the National Natural Science Foundation of China(Grant Nos.51379138 and 51609162)
文摘Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.
基金Supported by the Dongguk University Research Fund of 2016。
文摘AIM:To introduce a new surgical technique,air-bubble technique for the management of posterior capsule rupture(PCR)and to evaluate the safety and efficacy of the technique.METHODS:A retrospective case series analysis of 24 eyes of 24 patients,in which the air bubble technique was used for the management of PCR,was performed.Once PCR occurred,a dispersive ophthalmic viscosurgical device(OVD)was injected into the tear.And small volumes(0.2-0.3 mL)of air bubbles were injected beneath the OVD.The air bubble served as a physical barrier and supported the posterior capsule.RESULTS:After surgery,none of the patients had serious complications during the follow-up period of 1 y.Extension of the PCR size occurred in only 2 cases,and additional OVD injection was required only in 3 cases.Air bubbles imparted great stability to the nuclear pieces and the posterior capsule.CONCLUSION:The air-bubble technique may be considered a safe and effective procedure for managing a PCR.It may be of value to the inexperienced cataract surgeon.
基金financially supported by the National Natural Science Foundation of China (Nos. 51221462, 51134022,51174203 and 51074156)the National Basic Research Program of China (No. 2012CB214904)China Postdoctoral Science Foundation (No. 2013M531430)
文摘Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D b < 66 mm and 40 mm < D b < 69 mm with the magnetite powder of 0.3 mm+0.15mm and 0.15mm+0.074mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1mm fine coal as medium solids were utilized to carry out the separation experiment on 6-50mm raw coal. The results show that an optimal separation density d P of 1.73g/cm 3 with a probable error E of 0.07g/cm 3 and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.
基金supported by the National Natural Science Foundation of China (Grant Nos.10804050 and 10874086)the Ministry of Education of China (Grant Nos.20060284035 and 705017)
文摘We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are particularly investigated in various cases for distinguishing efficiently the acoustic localisation from the effects of acoustic absorption caused by the viscosity of medium. The numerical results reveal the phenomenon of 'phase transition' characterized by an unusual collective oscillation of bubbles, which is an effective criterion to unambiguously identify the acoustic localisation in the presence of viscosity. Within the localisation region, the phenomenon of phase transition persists, and a remarkable decrease in the fluctuation of the oscillation phases of bubbles is observed. The localisation phenomenon will be impaired by the enhancement of the viscosity factors, and the extent to which the acoustic wave is localised may be determined by appropriately analyzing the values of the oscillation phases or the amount of reduction of the phase fluctuation. The results are particularly significant for the practical experiments in an attempt to observe the acoustic localisation in such a medium, which is in general subjected to the interference of the great ambiguity resulting from the effect of acoustic absorption.
文摘In this paper, a series of experiments were carried out on the air concentration distribution. In the cavity zone, the air bubble frequency distribution was similar to the air concentration distribution. The air bubble frequency increased from the bottom and then decreased near the tmaerated black water region. The position of the maximum air bubble frequencyfmax moved downwards. At the air-water cross section, the relationship between the air bubble frequency and the air concentration was self-similar, the position of the maximum air bubble frequency caused by the air-water discontinuity gradually approached C = 0.50 with the development of aeration. Meanwhile, the dimensionless air bubble frequency in the cavity zone followed a parabolic function.
基金supported by the National Natural Science Foundation of China(Grant No.42271312,41201058)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA20070102)+1 种基金the National Key R&D Program of China(Grant No.2018YFB1307504)the Science and Technology Program of Tibet Autonomous Region of China(Grant No.XZ202101ZD0014G).
文摘Theδ18O of ice core enclosed gaseous oxygen(δ18Obub)has been widely used for climate reconstruction in polar regions.Yet,less is known about its climatic implication in the mountainous glaciers as the lack of continuous record.Here,we present a long-term,continuousδ18Obub record from the Tanggula glacier in the central Tibetan Plateau(TP).Based on comparisons of its variation with regional climate and glacier changes,we found that there was a good correlation between the variation of theδ18Obub in this alpine ice core and the accumulation and melting of this glacier.The more developed the firn layer on glacier surface,the more positive theδ18Obub.Conversely,the more intense the glacier melting,the more negative theδ18Obub.Combined with the chronology of ice core enclosed gases,the glacier variations since the late Holocene in the central TP were reconstructed.The result showed that there were four accumulation and three deficit periods of glaciers in this region.The strongest glacier accumulation period was 1610-300 B.C.,which corresponds to the Neoglaciation.The most significant melting period was the last 100 years,which corresponds to the recent global warming.The Medieval Warm Period was relatively significant in the central TP.However,during the Little Ice Age,there was no significant glacier accumulation in the central TP,and even short deficit events occurred.Comparisons of the late Holocene glacier variation in the central TP with glacier and climate variations in the TP and the Northern Hemisphere showed that it was closely related to the North Atlantic Oscillation.
基金This work was supported by the Jiangsu Natural Science Fund-Youth Fund(BK20190639)National Nature Science Foundation of China(Nos.21978318,51904300,and 51922106)National Key R&D Program of China(2020YFC1908803).
文摘Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements.The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness.The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning.Maximum adhesion forces between water and surfaces were 111.70,125.48,and 136.42μN when the roughness was 0.23,0.98,and 2.79 μm,respectively.In contrast,under a liquid environment,the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water.Maximum adhesion forces of increasing roughness were 97.14,42.76,and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48,145.84,and 121.02 lN between oil droplet and surfaces,respectively.Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.
文摘The sudden transition from a high-velocity, supercritical open channel flow into a slow-moving sub-critical flow is a hydraulic jump. Such a flow is characterised by a sudden rise of the free-surface, with some strong energy dissipation and air entrainment, waves and spray. New two-phase flow measurements were performed in the developing flow region using a large-size facility operating at large Reynolds numbers. The experimental results demonstrated the complexity of the flow with a developing mixing layer in which entrained bubbles are advected in a high shear stress flow. The relationship between bubble count rates and void fractions was non-unique in the shear zone, supporting earlier observations of some form of double diffusion process between momentum and air bubbles. In the upper region, the flow consisted primarily of water drops and packets sur-rounded by air. Visually significant pray and splashing were significant above the jump roller. The present study is the first com-prehensive study detailing the two-phase flow properties of both the bubbly and spray regions of hydraulic jumps, a first step towards understanding the interactions between bubble entrainment and droplet ejection processes.
基金supported by the National Natural Science Foundation of China (40671044)the Ministry of Science and Technology of China (2005CB422004)
文摘A high-resolution 2ooo-year methane record has been constructed from an ice core recovered at 7200 m a.s.1, on the Dasuopu Glacier in the central Himalayas. This sub-tropical methane record reveals an increasing trend in the concentration of methane during the industrial era that is similar to observations from polar regions. However, we also observed the differences in the atmospheric methane mixing ratio between this monsoon record and those from polar regions during pre-industrial times. In the time interval o N 1850 A.D., the average methane concentration in the Dasuopu ice core was 782±40 ppbv and the maximum temporal variation exceeded 200 ppbv. The difference gradient of methane concentration in Dasuopu ice core with Greenland and Antarctica cores are 66±40 ppbv and 107±40 ppbv, respectively. This suggests that the tropical latitudes might have acted as a major global methane source in preindustrial times. In addition, the temporal fluctuation of the pre-industrial methane records suggests that monsoon evolution incorporated with high methane emission from south Asia might be responsible for the relatively high methane concentration observed in the Dasuopu ice core around A.D. 800 and A.D. 1600. These results provide a rough understanding of the contribution of tropical methane source to the global methane budget and also the relationship betweenatmospheric methane and climate change.
文摘On the basis of the mineralizing mechanism of froth cyclone, this paper expounds that the froth cyclone flotation process is accomplished in a limited centrifugal field. The main feature of air bubble mineralizing in the froth cyclone is a synthetic mineralizing process, of which the non collision mineralization of minute air bubble separated out dominates, supplemented with the collision mineralization. Moreover, this paper points out that the hydrophobic separated out and centrifugal force strengthen the selectivity of fine coal particle, accelerate the flotation speed and improve the slime recovery.
文摘Cavitation in plants is caused by development of air bubbles, which is related to their equilibrium and development. There is a univariate cubic equation for bubble balance. New root formula of this kind of equation was proposed by Shenjin Fan, which is simpler than the Caldan’s. Using Shenjin formulas and taking water pressure <em>P</em><sub>1</sub> as an independent variable, this paper gives the exact solution of the equation under certain conditions. The stability of the equilibrium of an air bubble in its different radius ranges is obtained by the way different from the previous. This kind of cavitation includes two types: First type may be caused by the growth of pre-existent air bubbles;Second type is air seeding, here defined as the sucking of air bubbles from already gas-filled conduits. For air seeding three ways of cavitation have been proposed. For the first type this paper puts forward that two ways of cavitation can occur, which are the same with the first two ways of air seeding except of air reservoirs. Moreover, for the first way of the first type, the range of water pressures is the same with that of the first way of air seeding. For the second way of the first type the range of water pressures is much wider, or the pressure range equals the pressure sum of the second and third ways of air seeding. Through the specific data the relationship between the two types is given.
文摘Although hydraulic drives have an advantage of high power density, volumetric shrinkage of hydraulic fluids due to pressure causes various disadvantages such as delay of hydraulic response and compression energy loss. Hydraulic fluids of new concept, high bulk modulus oils, have been developed as a new approach to improve the performance of a hydraulic servo system and verified. In this paper, practical performances of high bulk modulus oil, such as oil temperature rise during pump test, air bubbles generation by ultrasonic wave vibration, oxidation stability and anti-wear property, were studied. And the new oil was confirmed to have excellent practical performances besides advantages in pressure response and volumetric efficiency of pumps. Various new applications of the new oil are promising.
基金supported by the Ministry of Science and Technology of China (Grant Nos. 2007CB714105 and 2008BAB29B04)
文摘The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction.The bubble-bubble interaction can be considered in two different conditions.The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small,and away from the air bubble if the air bubble is relatively large.The two zones are identified in the bubble-boundary interaction,and they are the danger zone and the safety zone.The relative position,the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction,which can be considered in several conditions according to the responses of the bubbles.Air jets are found to penetrate into the cavitation bubbles.The cavitation bubble and the air bubble(air jet) move in their own way without mixing.The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary.The influence of the air bubble and the influence of the boundary may be combined,like some thing of a vector.
基金Project supported by the National Key Basic Research Development Program of China(973 Program,Grant No.2013CB035905)the National Natural Science Foundation of China(Grant No.51179114)
文摘Experiments are carried out by using high-speed photography to investigate the interaction between the spark-generated cavitation bubble and the air bubble in its surrounding fluid. Three problems are discussed in detail: the impact of the air bubble upon the development of the cavitation bubble, the evolution of the air bubble under the influence of the cavitation bubble, and the change of the fluid pressure during the development of a micro jet of the cavitation bubble. Based on the experimental results, under the condition of no air bubble present, the lifetime of the cavitation bubble from expansion to contraction increases with the increase of the maximum radius. On the other hand, when there is an air bubble present, different sized cavitation bubbles have similarity with one another generally in terms of the lifetime from expansion to contraction, which does not depend on the maximum radius. Also, with the presence of an air bubble, the lifetime of the smaller cavitation bubble is extended while that of the bigger ones reduced. Furthermore, it is shown in the experiment that the low pressure formed in the opposite direction to the cavitation bubble micro jet makes the air bubble in the low pressure area being stretched into a steplike shape.
基金supported by the National Natural Science Foundation of China(Grant No.51409187)the Fundamental Research Funds for the Central Universities(Grant No.2016B09914)
文摘Over the past 60 years, the air concentration in water has been considered as a control index of cavitation erosion reduction and widely used in the designs of hydraulic structures. However, the mechanism of air entrainment against cavitation erosion has been paid good attention to. In the present work, the effect of air bubble size on cavitation erosion reduction was experimentally investigated. A device with micron-scale orifice diameters(10, 20 and 50 μm in size) was specially designed to introduce air bubbles into water. The experiments about the effect of air bubble size were conducted by means of a vibratory apparatus, including the behavior of formation and movement for single air bubble, the characteristics of cavitation erosion reduction at different air entrainment conditions. The findings demonstrate that high air concentration has significant effects on cavitation erosion reduction.But, a notable problem was that the size of air bubbles is of outstanding effect on cavitation erosion reduction. Small air bubbles support to alleviate cavitation erosion, even at same air concentration.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50809015)
文摘The wave dissipating performance of air bubble breakwaters with different layouts is studied by experimental and numerical methods in this article. Based on the assumpation that the mixture of air and water is regarded as a variable density fluid, the mathematical model of the air bubble breakwater is built. The numerical simulation results are compared with the experimental data, which shows that the mathematical model is reasonable for the transmission coefficient Ct m. The influencing factors are studied experimentally and numerically, including the incident wave height H i, the incidentt wave period T , the air amount Qm , the submerged pipe depth D and the single or double air discharging pipe structure. Some valuable conclusions are obtained for further research of the mechanism and practical applications of air bubble breakwaters.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0401901)the National Natural Science Foundation of China(Grant No.51409180).
文摘The cavitation erosion is one of the common damage modes in water engineering.The study of the interaction among cavitation bubbles,air bubbles and the wall is of great significance for understanding the mechanism of the air entrainment to alleviate the cavitation and to enhance the cavitation erosion mitigation effect of aeration.By using the high-speed camera,the regular patterns of the collapse of cavitation bubbles in the vicinity of the wall and the air bubbles are studied in this paper.It is shown that in the vicinity of air bubbles,the cavitation bubbles may only collapse towards or from air bubbles,while under the dual impacts of air bubbles and the wall,the direction of collapse of the cavitation bubbles depends on the combined vector of the impact forces of the air bubbles and the wall.When the air bubbles are very close to the cavitation bubbles,the air bubbles will be penetrated and stretched by the cavitation bubbles,when the distance between them is short enough,the cavitation bubbles and the air bubbles will connect to form gas-type cavitation bubbles,and the collapse strength will be significantly decreased,when there are two air bubbles near the cavitation bubbles,they may even be penetrated successively by the cavitation bubbles.Thus it can be concluded that during the air entrainment to alleviate the cavitation,the number of air bubbles is more important than the total air concentration.
基金Acknowledgements This research is fimded by the National Natural Science Foundation of China (Grant No. 51378141) and the Science and Technology Department of Heilongjiang Province, China (Grant No. PS13H05). The authors would like to express thanks to their friends operating the Huainan first water treatment plant for their generous support. Sincerest thanks also to the staff at the Central Laboratory of Huainan Capital Water for their support in water sample analysis.
文摘A novel, functionalized bubble surface can be obtained in dissolved air flotation (DAF) by dosing chemicals in the saturator. In this study, different cationic chemicals were used as bubble surface modifiers, and their effects on natural organic matter (NOM) removal from river water were investigated. NOM in the samples was fractionated based on molecular weight and hydrophobicity. The disinfection byproduct formation potentials of each fraction and their removal efficiencies were also evaluated. The results showed that chitosan was the most promising bubble modifier compared with a surfactant and a synthetic polymer. Tiny bubbles in the OAF pump system facilitated the adsorption of chitosan onto microbubble surfaces. The hydrophobic NOM fraction was preferentially removed by chitosan-modified bubbles. Decreasing the recycle water pH from 7.0 to 5.5 improved the removal of hydrophilic NOM with low molecular weight. Likewise, hydrophilic organic compounds gave high dihaloacetic acid yields in raw water. An enhanced reduction of haloacetic acid precursors was obtained with recycle water at pH values of 5.5 and 4.0. The experimental results indicate that NOM fractions may interact with bubbles through different mechanisms. Positive bubble modification provides an alternative approach for OAF to enhance NOM removal.