The internal pressure within fission gas bubbles(FGBs)in irradiated nuclear fuels drives mechanical interactions with the surrounding fuel skeleton.To investigate the micromechanical stress fields in irradiated nuclea...The internal pressure within fission gas bubbles(FGBs)in irradiated nuclear fuels drives mechanical interactions with the surrounding fuel skeleton.To investigate the micromechanical stress fields in irradiated nuclear fuels containing pressurized FGBs,a mechanical constitutive model for the equivalent solid of FGBs was developed and validated.This model was based on the modified Van der Waals equation,incorporating the effects of surface tension.Using this model,the micromechanical fields in irradiated U-10Mo fuels with randomly distributed FGBs were calculated during uniaxial tensile testing via the finite element(FE)method.The macroscopic elastic constants of the irradiated U-10Mo fuels were then derived using homogenization theory,and the influences of bubble pressure,bubble size,and porosity on these constants were examined.Results show that adjacent FGBs exhibit mechanical interactions,which leads to distinct stress concentrations in the surrounding fuel skeleton.The macroscopic elastic constants of irradiated U-10Mo fuels decrease with increasing the macroscopic porosity,which can be quantitatively described by the Mori-Tanaka model.In contrast,bubble pressure and size have negligible effects on these constants.展开更多
Sound speed is essential for leakage detection in liquid pipelines when using acoustic methods,which can be significantly influenced by gas bubbles generated from leakage.The propagation characteristics and mechanism ...Sound speed is essential for leakage detection in liquid pipelines when using acoustic methods,which can be significantly influenced by gas bubbles generated from leakage.The propagation characteristics and mechanism of acoustic waves in horizontal liquid pipelines containing gas bubbles are studied in detail in the present paper.The effect of sound wave frequency,bubble size and bubble distribution pattern on sound speed is studied through numerical simulations.The results show that the acoustic wave generated by leakage of liquid pipelines containing gas bubbles is a multi-frequency signal,and the energy of the signal is mainly concentrated within 200 Hz.In the low-frequency range,the propagation of sound waves has almost no dispersion in bubbly liquid.Sound speed at a certain void fraction is not constant,which is related to the bubble size and distribution pattern.The bubble size affects the gasliquid heat transfer equilibrium,during which sound speed is affected.For this reason,a thermodynamic correction factor is proposed,which enables the accuracy of the sound speed calculation to reach98.2%.What's more,sound speed increases non-linearly with the reduction of the bubble distribution space in the pipeline axial direction.This paper establishes a theoretical calculation model of sound speed based on the bubble distribution pattern in the pipeline axial direction,which is in good agreement with the numerical calculation results.The results of this paper provide the basis for applying acoustic leak detection technology in liquid pipelines containing gas bubbles.展开更多
A model of intra-grain fission gas bubble growth in U_(3)Si_(2) coupled with defect microstructure is generalized to take into account the influence of point defect sinks and defect clustering.The dynamics of bubble g...A model of intra-grain fission gas bubble growth in U_(3)Si_(2) coupled with defect microstructure is generalized to take into account the influence of point defect sinks and defect clustering.The dynamics of bubble growth and defect structure properties are studied under different irradiation conditions.The influence of temperature and flux on bubble growth,defect ensemble evolution,and changes in material properties(elastic moduli and thermal degradation factor)are examined in detail.The universality of the bubble size distribution and the crossover of dynamical regimes of bubble growth are studied under various irradiation conditions.It is shown that a change in the dominant(fission gas atom-or vacancymediated)mechanism of bubble growth results in a crossover from a parabolic to a sub-parabolic bubble size growth law.The proposed modification of the rate theory model provides more accurate predictions and more detailed insight into fuel performance,especially fission gas behavior in crystalline U_(3)Si_(2).展开更多
This paper presents an algorithm of automatic bubble image segmentation using the improved ant colony optimization methodology. The ant colony optimization method is a metaheuristic algorithm, and has been applied in ...This paper presents an algorithm of automatic bubble image segmentation using the improved ant colony optimization methodology. The ant colony optimization method is a metaheuristic algorithm, and has been applied in many fields. To reveal the versatility and appropriateness of automatic bubble image segmentation, the fuzzy clustering analysis method is employed in ant colony optimization algorithm. Compared with the well-known image feature extraction operators such as SUSAN and Canny, the proposed method can comparatively suitable to extract the gas bubbles image edge features. The experimental results show that the proposed method is effective and reliable, and can achieve satisfactory image edge extraction effect.展开更多
In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted ...In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted in the fast and steady ice growth stages. Ice pieces were used to observe ice crystals and gas bubbles in ice, and to measure the ice density. Vertical profiles of the type and size of ice crystals, shape and size of gas bubbles, and gas bubble content, as well as the ice density, were obtained. The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice; the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages; the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content vary with the ice growth stage; and the ice density decreases with the increase of the gas bubble content.展开更多
AIM:To investigate the incidence and the predisposing factors of anterior chamber(AC)gas bubbles during femtosecond laser(FS)flap creation for laser in situ keratomileusis(LASIK).METHODS:All patients who underwent FS-...AIM:To investigate the incidence and the predisposing factors of anterior chamber(AC)gas bubbles during femtosecond laser(FS)flap creation for laser in situ keratomileusis(LASIK).METHODS:All patients who underwent FS-LASIK surgery at CMU LASIK Center between January 2013 and May 2016 were retrospective reviewed.Preoperative and intraoperative data including keratometry,white-towhite(WTW)corneal diameter,flap parameters(diameter,thickness,hinge position,and tunnel length)and pulse energy were reviewed and compared between incident group and control group.To determine the risk factors,univariate and multivariate conditional logistic regression were used;the eye was unit of analysis.RESULTS:The incidence of AC gas bubbles was 1.6%(22 out of 1378 eyes).The median WTW in the AC bubbles group was 11.5 mm(range 11.1-12.1),which was significantly different from the control group(11.7 mm,range 10.5-12.8,P=0.021).The result of the median WTW minus the flap diameter in the AC bubbles group was 2.5 mm(range 2.1-3.2),which was statistically different to the control group(2.7 mm,range 1.5-3.8,P=0.008).The logistic regression analysis showed that the result of the WTW minus the flap diameter in the AC bubbles group had an adjusted odds ratio of 0.204(95%CI;0.056-0.747,P=0.016).CONCLUSION:Development of AC gas bubbles during FS flap creation is not an uncommon event in Asian eyes which typically have a small WTW.The flap diameter when adjusted relatively to the WTW is a predisposing factor to the possibility of AC gas bubbles occurrence.展开更多
Electrochemical gas evolution reactions are common but essential in many electrochemical processes including water electrolysis.During these processes,gas bubbles are constantly nucleating on reaction interfaces in el...Electrochemical gas evolution reactions are common but essential in many electrochemical processes including water electrolysis.During these processes,gas bubbles are constantly nucleating on reaction interfaces in electrolyte and consequently exert an impact on catalysts and the performance.In the past few decades,extensive studies have been conducted to characterize bubbles with emerging advanced technologies,manage behaviors of bubbles,and apply bubbles to various domains.In this review,we summarize representative discoveries as well as recent advancements in electrochemical gas evolution reactions from the perspective of gas bubbles.Finally,we end up this review with a profound outlook on future research topics from the combination of experiments and theoretical techniques,non-negligible bubble effects,gravity-free situation,and reactions under practical industrial conditions.展开更多
For forced radial oscillations of gas bubbles in liquids, a more rigorous expression of the acoustic damping constant based on Keller＇s equation is developed. Comparison with those in published papers is also made. T...For forced radial oscillations of gas bubbles in liquids, a more rigorous expression of the acoustic damping constant based on Keller＇s equation is developed. Comparison with those in published papers is also made. The expression offered in this paper will improve the predictions of total damping constant in particular for high frequencies and large bubbles, i.e., large ωR0 / c1 （ ω is the frequency of driving sound field, Ro is the equilibrium bubble radius, c1 is the sound speed in the liquid）. Examples in ultrasound imaging and acoustical oceanography are demonstrated.展开更多
This paper presents formulae and explanation about the growth of a convective gas bubble in the blood and other tissues of divers who surface too quickly, concentration distribution around the growing bubble is also p...This paper presents formulae and explanation about the growth of a convective gas bubble in the blood and other tissues of divers who surface too quickly, concentration distribution around the growing bubble is also presented. The formulae are valid all over the growth stages, i.e. under variable ambient pressure while the diver is ascending, and under constant ambient pressure at diving stops or at sea level. The mathematical model is solved analytically by using the method of combined variables. The growth process is affected by tissue diffusivity, concentration constant and the initial void fraction, which is the dominant parameter. Results show that, the time of the complete growth, in the convective growth model, is shorter than those earlier presented by Mohammadein and Mohamed [Concentration distribution around a growing gas bubble in tissue, Math. Biosci. 225（1） （2010） 11-17] and Srinivasan et al. [Mathematical models of diffusion- limited gas bubble dynamics in tissue, J. Appl. Physiol. 86 （1999） 732-741] for the growth of a stationary gas bubble, this explains the effect of bubble motion on consuming the oversaturated dissolved gas from the tissue into growing bubble which leads to increment in the growth rate to be more than those presented in the previous stationary models.展开更多
A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalen...A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalent circuit was modeled with Matlab/Simulink simulation software. The time-series signals of cell voltage and anode current were obtained under different bubble conditions, and analyzed by spectral and statistical analysis methods. The simulation results show that higher bubble release frequency has a significant effect on the cell voltage oscillations. When the bubble coverage of one anode block exceeds 80%, the cell voltage may exceed its normal fluctuation amplitude. The simulation also proves that the anode effect detected by computer in actual production is mainly the whole cell anode effect.展开更多
The semi-solid slurry of AZ91 D magnesium alloy was prepared by gas bubbling process.The effect of processing parameters,including gas flow rate,cooling rate and stirring end temperature,on microstructure of AZ91 D se...The semi-solid slurry of AZ91 D magnesium alloy was prepared by gas bubbling process.The effect of processing parameters,including gas flow rate,cooling rate and stirring end temperature,on microstructure of AZ91 D semi-solid slurry was investigated.With increasing the gas flow rate from 0 to 5 L/min,the average size of primary α-Mg particles decreases from 119.1 to77.2μm and the average shape factor increases continuously from 0.1 to 0.596.The formation of non-dendritic primary α-Mg particles during gas bubbling is the result of combined effects of dendrite fragmentation and copious nucleation.With increasing the cooling rate from 3.6 to 14.6℃/min,the average particle size of primary α-Mg phase decreases from 105.0 to 68.1μm while the average shape factor peaks at 9.1℃/min.Both high and low cooling rates can induce dendritic growth of primary α-Mg particles.Changing the stirring end temperature from 590 to 595℃ has little effect on the average size and shape factor of primary α-Mg particles in AZ91 D semi-solid slurry.The insensitivity of semi-solid microstructures to the stirring end temperature is attributed to the sufficient quantity of primary particles formed in the melt.展开更多
The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF6 b...The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF6 bubble is studied by the numerical method VAS2D. As a validation, the experiments of a SF6 bubble accelerated by a planar shock were performed. The results indicate that, due to the mismatch of acoustic impedance, the way of jet formation in heavy gas bubble with different species is diversified under the same initial condition. With respect to the same bubble, the manner of jet formation is also distinctly different under different shock strengths. The disparities of the acoustic impedance result in different effects of shock focusing in the bubble, and different behaviors of shock wave inside and outside the bubble. The analyses of the wave pattern and the pressure variation indicate that the jet formation is closely associated with the pressure perturbation. Moreover, the analy- sis of the vorticity deposition, and comparisons of circulation and baroclinic torque show that the baroclinic vorticity also contributes to the jet formation. It is concluded that the pres- sure perturbation and baroclinic vorticity deposition are the two dominant factors for the jet formation in shock-heavy gas bubble interaction.展开更多
In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt th...In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification,and the samples of semi-solid slurry were taken by the rapid quenching method.The results show that fine and sphericalα-Mg particles can be obtained under rotating gas bubble stirring treatment.The process parameters such as gas flow rate,cooling rate and rotation speed have significant influence on the morphology of primary solid particles.After rotating gas bubble stirring treatment,the higher the particle density,the finer and rounder the primaryα-Mg particles.The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.展开更多
A novel technique of introducing gas bubble stirring during solidification was studied to prepare Al-Si semi-solid slurry. The microstructure evolution of the slurry during slow cooling process after stirring was inve...A novel technique of introducing gas bubble stirring during solidification was studied to prepare Al-Si semi-solid slurry. The microstructure evolution of the slurry during slow cooling process after stirring was investigated. The effects of the solidification rate on the microstructure of the semi-solid slurry were investigated under three different solidification conditions. The results show that fine non-dendritic slurry can be obtained using the gas bubble stirring method. Ripening and coarsening of primary Al grains are observed during the slow cooling process, and at last coarsened eutectic Si appears. Primary Al grains with different sizes and eutectic Si are obtained, corresponding to three different solidification rates.展开更多
Numerous irradiation-induced gas bubbles are created in the nuclear fuel during irradiation, leading to the change of microstructure and the degradation of mechanical and thermal properties. The grain size of fuel is ...Numerous irradiation-induced gas bubbles are created in the nuclear fuel during irradiation, leading to the change of microstructure and the degradation of mechanical and thermal properties. The grain size of fuel is one of the important factors affecting bubble evolution. In current study, we first predict the thermodynamic behaviors of point defects as well as the interplay between vacancy and gas atom in both UO_(2) and U_(3)Si_(2) according to ab initio approach. Then, we establish the irradiation-induced bubble phase-field model to investigate the formation and evolution of intra-and inter-granular gas bubbles. The effects of fission rate and temperature on the evolutions of bubble morphologies in UO_(2) and U_(3)Si_(2) have been revealed. Especially, a comparison of porosities under different grain sizes is examined and analyzed. To understand the thermal conductivity as functions of grain size and porosity, the heat transfer capability of U_(3)Si_(2) is evaluated.展开更多
Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid EulerianEulerian two-fluid model(TFM)simulations of gas-solid flow hydrodynamics in fluidized bed reactors.Although numer...Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid EulerianEulerian two-fluid model(TFM)simulations of gas-solid flow hydrodynamics in fluidized bed reactors.Although numerous mesoscale drag models have been reported in the literature,a systematic comparison of their prediction capability from the perspective of heterogeneity analysis is still lacking.In this study,in order to investigate the effect of several typical drag models on the hydrodynamic behaviors,the nonuniformity analysis and the sensitivity to material properties,extensive coarse-grid TFM simulations of a bubbling pilot-scale fluidized bed reactor are carried out.The results demonstrate that the mesoscale drag models outperform the empirical drag model in terms of nonuniformity due to the consideration of the influence of the mesoscale structures on the drag force in the bubbling region.Furthermore,the results reveal that our previously developed three-marker gradient-based drag model considering the solid concentration gradient exhibits satisfactory performance in predicting the bubbling flow hydrodynamics.Besides,the material-property-dependent drag model considering the explicit effect of material properties on drag corrections is most sensitive to the particle diameter.This work provides guideline for possible future improvements of mesoscale models to simulate gas-solid flow more accurately and universally.展开更多
Removal of non-metallic inclusions in molten steel is important from the viewpoint of improvement of quality, property and yield of the products. As a removal method of inclusions from molten metal, gas bubble flotati...Removal of non-metallic inclusions in molten steel is important from the viewpoint of improvement of quality, property and yield of the products. As a removal method of inclusions from molten metal, gas bubble flotation adhering inclusions is well known. Gas bubbling is particularly effective for the removal of fine inclusions. Water model experiment is reported the quantitative analysis of the removal ratio of dispersed particles removed from water by gas bubbles.展开更多
Mass transfer at hydrogen evolving mercury electrode has been studied by determining mass transfer coefficients of indicator ions as the function of current density of hydrogen evolution for various kinds of indica to...Mass transfer at hydrogen evolving mercury electrode has been studied by determining mass transfer coefficients of indicator ions as the function of current density of hydrogen evolution for various kinds of indica tor ions in sulphuric acid solution.Mercury adhering to metal substrates of Ni,Cu or Ag is used as mercury electrode to overcome its trembling during the electrolysis.The effect of difTerent indicator ions,electrode character istic,substrate material,diameter of electrode and temperature is examined.It is found that the transfer coefficient is proportional to the mass square root of current density of hydrogen evolution.展开更多
This paper presents experimental results from physical and mathematical simulation of liquid steel flow in the tundish adopting gas bubbling curtain substituting dam and industrial trials have been investigated based ...This paper presents experimental results from physical and mathematical simulation of liquid steel flow in the tundish adopting gas bubbling curtain substituting dam and industrial trials have been investigated based the experimental results. Physical and mathematical simulation results show the gas bubbling curtain can improve pattern of liquid flow in the tundish , accelerate inclusions flotation,and simultaneity metallurgy effect has been further improved when combining weir and turbulence inhibitor. The industrial trial results confirm that content of oxygen , nitrogen and inclusions in continuous casting billets have been reduced when gas bubbling curtain combining weir and turbulence inhibitor.展开更多
In the present study, the contribution of the gas bubbling filtration （GBF） process to the microporosity variation, microstructural characteristics and tensile properties of A356 aluminium alloy was investigated. Th...In the present study, the contribution of the gas bubbling filtration （GBF） process to the microporosity variation, microstructural characteristics and tensile properties of A356 aluminium alloy was investigated. The test specimens were fabricated through gravity casting in terms of the process variables： the degassing time, the impeller rotation and the aperture size of gas inlet hole. The density measurement and scanning electron microscope fractography analyses were conducted to evaluate the variation of the volumetric porosity and fractographic porosity with the GBF process, respec- tively. The fractographic porosity of the specimens can be minimised under specific GBF conditions in terms of the buoyant velocity and the absorbing capacity of gas bubbles, the inclusion of oxide films, whereas the volumetric porosity can be wholly reduced on the lapse of degassing time. The ultimate tensile strength （UTS） and elongation at optimal conditions were improved to approximately 30 MPa and 1.5% compared with no GBF treatment. Even though an extension of the degassing time and/or excessive stirring action of the melt may induce the inclusion of bifilm oxides and the increase of fractographic porosity, the tensile properties of over-treated specimens were maintained to a level which is similar to those that did not undergo GBF treatment due to the grain refinement accompanying with the GBF process. In addition, the defect susceptibility of UTS and elongation to microporosity variation could be remarkably improved at an optimal GBF condition.展开更多
基金National Natural Science Foundation of China(12135008,12132005)。
文摘The internal pressure within fission gas bubbles(FGBs)in irradiated nuclear fuels drives mechanical interactions with the surrounding fuel skeleton.To investigate the micromechanical stress fields in irradiated nuclear fuels containing pressurized FGBs,a mechanical constitutive model for the equivalent solid of FGBs was developed and validated.This model was based on the modified Van der Waals equation,incorporating the effects of surface tension.Using this model,the micromechanical fields in irradiated U-10Mo fuels with randomly distributed FGBs were calculated during uniaxial tensile testing via the finite element(FE)method.The macroscopic elastic constants of the irradiated U-10Mo fuels were then derived using homogenization theory,and the influences of bubble pressure,bubble size,and porosity on these constants were examined.Results show that adjacent FGBs exhibit mechanical interactions,which leads to distinct stress concentrations in the surrounding fuel skeleton.The macroscopic elastic constants of irradiated U-10Mo fuels decrease with increasing the macroscopic porosity,which can be quantitatively described by the Mori-Tanaka model.In contrast,bubble pressure and size have negligible effects on these constants.
基金supported by the National Natural Science Foundation of China[grant number 52274066]。
文摘Sound speed is essential for leakage detection in liquid pipelines when using acoustic methods,which can be significantly influenced by gas bubbles generated from leakage.The propagation characteristics and mechanism of acoustic waves in horizontal liquid pipelines containing gas bubbles are studied in detail in the present paper.The effect of sound wave frequency,bubble size and bubble distribution pattern on sound speed is studied through numerical simulations.The results show that the acoustic wave generated by leakage of liquid pipelines containing gas bubbles is a multi-frequency signal,and the energy of the signal is mainly concentrated within 200 Hz.In the low-frequency range,the propagation of sound waves has almost no dispersion in bubbly liquid.Sound speed at a certain void fraction is not constant,which is related to the bubble size and distribution pattern.The bubble size affects the gasliquid heat transfer equilibrium,during which sound speed is affected.For this reason,a thermodynamic correction factor is proposed,which enables the accuracy of the sound speed calculation to reach98.2%.What's more,sound speed increases non-linearly with the reduction of the bubble distribution space in the pipeline axial direction.This paper establishes a theoretical calculation model of sound speed based on the bubble distribution pattern in the pipeline axial direction,which is in good agreement with the numerical calculation results.The results of this paper provide the basis for applying acoustic leak detection technology in liquid pipelines containing gas bubbles.
基金supported by the Fund from Sichuan Science and Technology Program(Grant No.2024JDHJ0014)the Joint Funds of the National Natural Science Foundation in China(Grant No.U23B2071)the Fund from the Ministry of Education and Science of Ukraine(Grant No.0124U000551)。
文摘A model of intra-grain fission gas bubble growth in U_(3)Si_(2) coupled with defect microstructure is generalized to take into account the influence of point defect sinks and defect clustering.The dynamics of bubble growth and defect structure properties are studied under different irradiation conditions.The influence of temperature and flux on bubble growth,defect ensemble evolution,and changes in material properties(elastic moduli and thermal degradation factor)are examined in detail.The universality of the bubble size distribution and the crossover of dynamical regimes of bubble growth are studied under various irradiation conditions.It is shown that a change in the dominant(fission gas atom-or vacancymediated)mechanism of bubble growth results in a crossover from a parabolic to a sub-parabolic bubble size growth law.The proposed modification of the rate theory model provides more accurate predictions and more detailed insight into fuel performance,especially fission gas behavior in crystalline U_(3)Si_(2).
基金Sponsored by the"Liaoning Bai Qian Wan"Talents Program (Grant No.2007-186-25)the Program of Scientific Research Project of Liaoning Province Education Commission (Grant No.LS2010046)the National Commonweal Industry Scientific Research Project (Grant No.201003024)
文摘This paper presents an algorithm of automatic bubble image segmentation using the improved ant colony optimization methodology. The ant colony optimization method is a metaheuristic algorithm, and has been applied in many fields. To reveal the versatility and appropriateness of automatic bubble image segmentation, the fuzzy clustering analysis method is employed in ant colony optimization algorithm. Compared with the well-known image feature extraction operators such as SUSAN and Canny, the proposed method can comparatively suitable to extract the gas bubbles image edge features. The experimental results show that the proposed method is effective and reliable, and can achieve satisfactory image edge extraction effect.
基金supported by the National Natural Science Foundation of China (Grant No.50879008)the Open Fund of State Key Laboratory of Frozen Soil Engineering (Grant No. SKLFSE200904)+1 种基金the Vilho,Yrj and Kalle Visl Fund of the Finnish Academy of Sciences and Lettersthe Norwegian Research Council Project AMORA (Grant No.193592/S30)
文摘In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted in the fast and steady ice growth stages. Ice pieces were used to observe ice crystals and gas bubbles in ice, and to measure the ice density. Vertical profiles of the type and size of ice crystals, shape and size of gas bubbles, and gas bubble content, as well as the ice density, were obtained. The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice; the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages; the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content vary with the ice growth stage; and the ice density decreases with the increase of the gas bubble content.
文摘AIM:To investigate the incidence and the predisposing factors of anterior chamber(AC)gas bubbles during femtosecond laser(FS)flap creation for laser in situ keratomileusis(LASIK).METHODS:All patients who underwent FS-LASIK surgery at CMU LASIK Center between January 2013 and May 2016 were retrospective reviewed.Preoperative and intraoperative data including keratometry,white-towhite(WTW)corneal diameter,flap parameters(diameter,thickness,hinge position,and tunnel length)and pulse energy were reviewed and compared between incident group and control group.To determine the risk factors,univariate and multivariate conditional logistic regression were used;the eye was unit of analysis.RESULTS:The incidence of AC gas bubbles was 1.6%(22 out of 1378 eyes).The median WTW in the AC bubbles group was 11.5 mm(range 11.1-12.1),which was significantly different from the control group(11.7 mm,range 10.5-12.8,P=0.021).The result of the median WTW minus the flap diameter in the AC bubbles group was 2.5 mm(range 2.1-3.2),which was statistically different to the control group(2.7 mm,range 1.5-3.8,P=0.008).The logistic regression analysis showed that the result of the WTW minus the flap diameter in the AC bubbles group had an adjusted odds ratio of 0.204(95%CI;0.056-0.747,P=0.016).CONCLUSION:Development of AC gas bubbles during FS flap creation is not an uncommon event in Asian eyes which typically have a small WTW.The flap diameter when adjusted relatively to the WTW is a predisposing factor to the possibility of AC gas bubbles occurrence.
基金supported by the National Natural Science Foundation of China(No.51902101)the Youth Natural Science Foundation of Hunan Province(No.2021JJ40044)+2 种基金Natural Science Foundation of Jiangsu Province(No.BK20201381)Science Foundation of Nanjing University of Posts and Telecommunications(Nos.NY219144 and NY221046)the National College Student Innovation and Entrepreneurship Training Program(No.202210293171K).
文摘Electrochemical gas evolution reactions are common but essential in many electrochemical processes including water electrolysis.During these processes,gas bubbles are constantly nucleating on reaction interfaces in electrolyte and consequently exert an impact on catalysts and the performance.In the past few decades,extensive studies have been conducted to characterize bubbles with emerging advanced technologies,manage behaviors of bubbles,and apply bubbles to various domains.In this review,we summarize representative discoveries as well as recent advancements in electrochemical gas evolution reactions from the perspective of gas bubbles.Finally,we end up this review with a profound outlook on future research topics from the combination of experiments and theoretical techniques,non-negligible bubble effects,gravity-free situation,and reactions under practical industrial conditions.
基金supported by the UK EPSRC WIMRC(Grant No.RESCM 9219)the EPSRC WIMRC Ph.D.studentship(Grant No.RESCM9217)
文摘For forced radial oscillations of gas bubbles in liquids, a more rigorous expression of the acoustic damping constant based on Keller＇s equation is developed. Comparison with those in published papers is also made. The expression offered in this paper will improve the predictions of total damping constant in particular for high frequencies and large bubbles, i.e., large ωR0 / c1 （ ω is the frequency of driving sound field, Ro is the equilibrium bubble radius, c1 is the sound speed in the liquid）. Examples in ultrasound imaging and acoustical oceanography are demonstrated.
文摘This paper presents formulae and explanation about the growth of a convective gas bubble in the blood and other tissues of divers who surface too quickly, concentration distribution around the growing bubble is also presented. The formulae are valid all over the growth stages, i.e. under variable ambient pressure while the diver is ascending, and under constant ambient pressure at diving stops or at sea level. The mathematical model is solved analytically by using the method of combined variables. The growth process is affected by tissue diffusivity, concentration constant and the initial void fraction, which is the dominant parameter. Results show that, the time of the complete growth, in the convective growth model, is shorter than those earlier presented by Mohammadein and Mohamed [Concentration distribution around a growing gas bubble in tissue, Math. Biosci. 225（1） （2010） 11-17] and Srinivasan et al. [Mathematical models of diffusion- limited gas bubble dynamics in tissue, J. Appl. Physiol. 86 （1999） 732-741] for the growth of a stationary gas bubble, this explains the effect of bubble motion on consuming the oversaturated dissolved gas from the tissue into growing bubble which leads to increment in the growth rate to be more than those presented in the previous stationary models.
基金Project(2012BAE08B09)supported by the National Key Technology R&D Program of China
文摘A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalent circuit was modeled with Matlab/Simulink simulation software. The time-series signals of cell voltage and anode current were obtained under different bubble conditions, and analyzed by spectral and statistical analysis methods. The simulation results show that higher bubble release frequency has a significant effect on the cell voltage oscillations. When the bubble coverage of one anode block exceeds 80%, the cell voltage may exceed its normal fluctuation amplitude. The simulation also proves that the anode effect detected by computer in actual production is mainly the whole cell anode effect.
基金Project(51275295)supported by the National Natural Science Foundation of ChinaProjects(20120073120011,20130073110052)supported by the Research Fund for the Doctoral Program of Higher Education of China
文摘The semi-solid slurry of AZ91 D magnesium alloy was prepared by gas bubbling process.The effect of processing parameters,including gas flow rate,cooling rate and stirring end temperature,on microstructure of AZ91 D semi-solid slurry was investigated.With increasing the gas flow rate from 0 to 5 L/min,the average size of primary α-Mg particles decreases from 119.1 to77.2μm and the average shape factor increases continuously from 0.1 to 0.596.The formation of non-dendritic primary α-Mg particles during gas bubbling is the result of combined effects of dendrite fragmentation and copious nucleation.With increasing the cooling rate from 3.6 to 14.6℃/min,the average particle size of primary α-Mg phase decreases from 105.0 to 68.1μm while the average shape factor peaks at 9.1℃/min.Both high and low cooling rates can induce dendritic growth of primary α-Mg particles.Changing the stirring end temperature from 590 to 595℃ has little effect on the average size and shape factor of primary α-Mg particles in AZ91 D semi-solid slurry.The insensitivity of semi-solid microstructures to the stirring end temperature is attributed to the sufficient quantity of primary particles formed in the melt.
基金supported by the National Natural Science Foundation of China (10972214 and 11172278)the Fundamental Research Funds for the Central Universities (WK2090050014)
文摘The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF6 bubble is studied by the numerical method VAS2D. As a validation, the experiments of a SF6 bubble accelerated by a planar shock were performed. The results indicate that, due to the mismatch of acoustic impedance, the way of jet formation in heavy gas bubble with different species is diversified under the same initial condition. With respect to the same bubble, the manner of jet formation is also distinctly different under different shock strengths. The disparities of the acoustic impedance result in different effects of shock focusing in the bubble, and different behaviors of shock wave inside and outside the bubble. The analyses of the wave pattern and the pressure variation indicate that the jet formation is closely associated with the pressure perturbation. Moreover, the analy- sis of the vorticity deposition, and comparisons of circulation and baroclinic torque show that the baroclinic vorticity also contributes to the jet formation. It is concluded that the pres- sure perturbation and baroclinic vorticity deposition are the two dominant factors for the jet formation in shock-heavy gas bubble interaction.
基金This project is sponsored by National Natural Science Foundation of China(No.51275295)Funded Projects of SAST-SJTU Joint Research Centre of Advanced Aerospace Technology(No.USCAST2012-15)Research Fund for the Doctoral Program of Higher Education of China(No.20120073120011).
文摘In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification,and the samples of semi-solid slurry were taken by the rapid quenching method.The results show that fine and sphericalα-Mg particles can be obtained under rotating gas bubble stirring treatment.The process parameters such as gas flow rate,cooling rate and rotation speed have significant influence on the morphology of primary solid particles.After rotating gas bubble stirring treatment,the higher the particle density,the finer and rounder the primaryα-Mg particles.The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.
基金Project(50775085)supported by the National Natural Science Foundation of ChinaProject(M2009061)supported by Special Fund for Basic Research and Operating Expenses of Central College,ChinaProject(2008A610049)supported by the Natural Science Foundation of Ningbo City,China
文摘A novel technique of introducing gas bubble stirring during solidification was studied to prepare Al-Si semi-solid slurry. The microstructure evolution of the slurry during slow cooling process after stirring was investigated. The effects of the solidification rate on the microstructure of the semi-solid slurry were investigated under three different solidification conditions. The results show that fine non-dendritic slurry can be obtained using the gas bubble stirring method. Ripening and coarsening of primary Al grains are observed during the slow cooling process, and at last coarsened eutectic Si appears. Primary Al grains with different sizes and eutectic Si are obtained, corresponding to three different solidification rates.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.U2167217,12205286,and 11905025)the National MCF Energy Research and Development Program of China (Grant No.2018YFE0308105)。
文摘Numerous irradiation-induced gas bubbles are created in the nuclear fuel during irradiation, leading to the change of microstructure and the degradation of mechanical and thermal properties. The grain size of fuel is one of the important factors affecting bubble evolution. In current study, we first predict the thermodynamic behaviors of point defects as well as the interplay between vacancy and gas atom in both UO_(2) and U_(3)Si_(2) according to ab initio approach. Then, we establish the irradiation-induced bubble phase-field model to investigate the formation and evolution of intra-and inter-granular gas bubbles. The effects of fission rate and temperature on the evolutions of bubble morphologies in UO_(2) and U_(3)Si_(2) have been revealed. Especially, a comparison of porosities under different grain sizes is examined and analyzed. To understand the thermal conductivity as functions of grain size and porosity, the heat transfer capability of U_(3)Si_(2) is evaluated.
文摘Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid EulerianEulerian two-fluid model(TFM)simulations of gas-solid flow hydrodynamics in fluidized bed reactors.Although numerous mesoscale drag models have been reported in the literature,a systematic comparison of their prediction capability from the perspective of heterogeneity analysis is still lacking.In this study,in order to investigate the effect of several typical drag models on the hydrodynamic behaviors,the nonuniformity analysis and the sensitivity to material properties,extensive coarse-grid TFM simulations of a bubbling pilot-scale fluidized bed reactor are carried out.The results demonstrate that the mesoscale drag models outperform the empirical drag model in terms of nonuniformity due to the consideration of the influence of the mesoscale structures on the drag force in the bubbling region.Furthermore,the results reveal that our previously developed three-marker gradient-based drag model considering the solid concentration gradient exhibits satisfactory performance in predicting the bubbling flow hydrodynamics.Besides,the material-property-dependent drag model considering the explicit effect of material properties on drag corrections is most sensitive to the particle diameter.This work provides guideline for possible future improvements of mesoscale models to simulate gas-solid flow more accurately and universally.
文摘Removal of non-metallic inclusions in molten steel is important from the viewpoint of improvement of quality, property and yield of the products. As a removal method of inclusions from molten metal, gas bubble flotation adhering inclusions is well known. Gas bubbling is particularly effective for the removal of fine inclusions. Water model experiment is reported the quantitative analysis of the removal ratio of dispersed particles removed from water by gas bubbles.
基金supported by the Foundation of the State Education Commission for doctoral students
文摘Mass transfer at hydrogen evolving mercury electrode has been studied by determining mass transfer coefficients of indicator ions as the function of current density of hydrogen evolution for various kinds of indica tor ions in sulphuric acid solution.Mercury adhering to metal substrates of Ni,Cu or Ag is used as mercury electrode to overcome its trembling during the electrolysis.The effect of difTerent indicator ions,electrode character istic,substrate material,diameter of electrode and temperature is examined.It is found that the transfer coefficient is proportional to the mass square root of current density of hydrogen evolution.
文摘This paper presents experimental results from physical and mathematical simulation of liquid steel flow in the tundish adopting gas bubbling curtain substituting dam and industrial trials have been investigated based the experimental results. Physical and mathematical simulation results show the gas bubbling curtain can improve pattern of liquid flow in the tundish , accelerate inclusions flotation,and simultaneity metallurgy effect has been further improved when combining weir and turbulence inhibitor. The industrial trial results confirm that content of oxygen , nitrogen and inclusions in continuous casting billets have been reduced when gas bubbling curtain combining weir and turbulence inhibitor.
基金supported by the General Researcher Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology(2010-0022284)+1 种基金supported by the Development Program for Industrial Core-Technology through the Korea Evaluation Institute of Industrial Technology(KEIT)funded by the Ministry of Trade,Industry and Energy(10048817)
文摘In the present study, the contribution of the gas bubbling filtration （GBF） process to the microporosity variation, microstructural characteristics and tensile properties of A356 aluminium alloy was investigated. The test specimens were fabricated through gravity casting in terms of the process variables： the degassing time, the impeller rotation and the aperture size of gas inlet hole. The density measurement and scanning electron microscope fractography analyses were conducted to evaluate the variation of the volumetric porosity and fractographic porosity with the GBF process, respec- tively. The fractographic porosity of the specimens can be minimised under specific GBF conditions in terms of the buoyant velocity and the absorbing capacity of gas bubbles, the inclusion of oxide films, whereas the volumetric porosity can be wholly reduced on the lapse of degassing time. The ultimate tensile strength （UTS） and elongation at optimal conditions were improved to approximately 30 MPa and 1.5% compared with no GBF treatment. Even though an extension of the degassing time and/or excessive stirring action of the melt may induce the inclusion of bifilm oxides and the increase of fractographic porosity, the tensile properties of over-treated specimens were maintained to a level which is similar to those that did not undergo GBF treatment due to the grain refinement accompanying with the GBF process. In addition, the defect susceptibility of UTS and elongation to microporosity variation could be remarkably improved at an optimal GBF condition.
