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In our previous paper, we derived a new single bubble model including the effect of bulk viscosity. To confront it to experiments, single bubble dynamics was measured here in 30% (v/v) glycerol-water mixture under different acoustic amplitudes and compared to models including or not the effect of bulk viscosity. The results showed that calculated bubble dynamics were not significantly affected by the bulk viscosity within the experimental conditions used in this study. However, there was a noticeable delay for the first rebound when bulk viscosity was considered. The corresponding sonoluminescence intensities were collected and compared with theoretical predictions. The results did not allow to discriminate between the two models (one includes the effect of bulk viscosity, the other does not), confirming the negligible effect of bulk viscosity in this condition (30% (v/v) glycerol-water mixture). Due to the instability of a single bubble in higher viscosity solutions, we could not implement experiments that can discriminate between the two models. 相似文献
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This paper investigates the pulsations and translation of bubbles in a double-bubble system driven by burst ultrasound. Results illustrate that for two identical bubbles, decreasing the frequency of burst or increasing its amplitude can enhance the pulsations and improve the translation velocities of bubbles. In a certain scope, large bubble brings about fast translation velocity, but the velocity will fall down for too large bubble, such as the bubble with ambient radius over about its resonance radius. When the ambient radii of two bubbles are different, translation of the large bubble is smaller than that of the small bubble. In addition, the effect of initial distance between bubbles is described as well. If burst serials are used, shortening the time interval between each burst and improving the acoustic amplitude of bursts are beneficial for the translations of bubbles. 相似文献
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The cavitation-mediated bioeffects are primarily associated with the dynamic behaviors of bubbles in viscoelastic tissues, which involves complex interactions of cavitation bubbles with surrounding bubbles and tissues. The radial and translational motions, as well as the resultant acoustic emissions of two interacting cavitation bubbles in viscoelastic tissues were numerically investigated. Due to the bubble–bubble interactions, a remarkable suppression effect on the small bubble, whereas a slight enhancement effect on the large one were observed within the acoustic exposure parameters and the initial radii of the bubbles examined in this paper. Moreover, as the initial distance between bubbles increases, the strong suppression effect is reduced gradually and it could effectively enhance the nonlinear dynamics of bubbles, exactly as the bifurcation diagrams exhibit a similar mode of successive period doubling to chaos. Correspondingly, the resultant acoustic emissions present a progressive evolution of harmonics, subharmonics, ultraharmonics and broadband components in the frequency spectra. In addition, with the elasticity and/or viscosity of the surrounding medium increasing, both the nonlinear dynamics and translational motions of bubbles were reduced prominently. This study provides a comprehensive insight into the nonlinear behaviors and acoustic emissions of two interacting cavitation bubbles in viscoelastic media, it may contribute to optimizing and monitoring the cavitation-mediated biomedical applications. 相似文献
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The collapse of laser-induced bubbles in water is investigated by high speed photography at framing rates as high as 20 million frames per second. The case of a spherical bubble in an unbounded liquid is compared with the Gilmore model. Bubbles collapsing in front of a solid wall show a rich dynamics depending on their normalized distance. Unprecedented details are given of the generic sequence of events leading to multiple shock waves and bubble shape metamorphosis upon collapse. 相似文献
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In the present study, the accuracies of two different numerical approaches used to model the translational motion of acoustic cavitational bubble in a standing acoustic field are compared. The less accurate but less computational demanding approach is to decouple the equation of translational motion from the radial oscillation, and solve it by calculating the time-averaged forces exerted on the bubble for one acoustic cycle. The second approach is to solve the coupled ordinary differential equations directly, which provides more accurate results with higher computational effort. The investigations are carried out in the parameter space of the driving frequency, pressure amplitude and equilibrium radius. Results showed that both models are capable to reveal stable equilibrium positions; however, in the case of oscillatory solutions, the difference in terms of translational frequency may be more than three fold, and the amplitude of translational motion obtained by the time-averaged method is roughly 1.5 times higher compared to the time-resolved solution at particular sets of parameters. This observation implies that where the transient behaviour is important, the time-resolved approach is the proper choice for reliable results. 相似文献
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This study aims principally to assess numerically the impact of methanol mass transport (i.e., evaporation/condensation across the acoustic bubble wall) on the thermodynamics and chemical effects (methanol conversion, hydrogen and oxygenated reactive species production) of acoustic cavitation in sono-irradiated aqueous solution. This effect was revealed at various ultrasound frequencies (from 213 to 1000 kHz) and acoustic intensities (1 and 2 W/cm2) over a range of methanol concentrations (from 0 to 100%, v/v). It was found that the impact of methanol concentration on the expansion and compression ratios, bubble temperature, CH3OH conversion and the molar productions inside the bubble is frequency dependent (either with or without consideration of methanol mass transport), where this effect is more pronounced when the ultrasound frequency is decreased. Alternatively, the decrease in acoustic intensity decreases clearly the effect of methanol mass transport on the bubble sono-activity. When methanol mass transfer is eliminated, the decrease of the bubble temperature, CH3OH conversion and the molar yield of the bubble with the rise of methanol concentration was found to be more amortized as the wave frequency is reduced from 1 MHz to 213 kHz, compared to the case when the mass transport of methanol is taken into account. Our findings indicate clearly the importance of incorporating the evaporation and condensation mechanisms of methanol throughout the numerical simulations of a single bubble dynamics and chemical activity. 相似文献
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Many models have been established to study the evolution of the bubble dynamics and chemical kinetics within a single acoustic cavitation bubble during its oscillation. The content of the bubble is a gas medium that generates the evolution of a chemical mechanism governed by the internal bubble conditions. These gases are described by a state equation, linking the pressure to the volume, temperature and species amounts, and influencing simultaneously the dynamical, the thermal and the mass variation in the cavitation bubble. The choice of the state equation to apply has then a non-neglected effect on the obtained results. In this paper, a comparative study was conducted through two numerical models based on the same assumptions and the same scheme of chemical reactions, except that the first one uses the ideal gas equation to describe the state of the species, while the second one uses the Van der Waals equation. It was found that though the dynamic of the bubble is not widely affected, the pressure and temperature range are significantly increased when passing from an ideal gas model to a real one. The amounts of chemical products are consequently raised to approximately the double. This observation was more significant for temperature and pressure at low frequency and high acoustic amplitude, while it is noticed that passing from ideal gas based approach to the Van der Waals one increases the free radicals amount mainly under high frequencies. When taking the results of the second model as reference, the relative difference between both results reaches about 60% for maximum attained temperature and 100% for both pressure and free radicals production. 相似文献
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In the present paper, the collapsing dynamics of a laser-induced cavitation bubble near the edge of a rigid wall is experimentally investigated with a high-speed photography system. For a symmetrical setup, the two primary control parameters of the bubble collapsing behavior include the equivalent maximum bubble radius and the distance between the bubble and the edge of the rigid wall. Based on the bubble interface deformation during the collapsing process, three typical cases are identified for the categorization of the phenomenon with the influences of the parameters revealed. Through a quantitative analysis of the obtained high-speed photos, the motions of the bubble interface in different directions are given together with the calculations of the bubble centroid. The primary findings of the present paper could be summarized in terms of the bubble-edge distance as follows. When the bubble is close to the edge, the movement of the bubble interface near the edge will be restricted with a clear neck formation in the middle part of the bubble. For this case, the edge could delay the bubble collapsing time up to 22% of the Rayleigh collapsing time. When the bubble is of the medium distance to the edge, the differences of the expansion or shrinkage of the bubble interface among different directions will be reduced with an olive-shaped bubble formed during the collapsing process. For this range of parameters, the bubble moves rapidly toward the edge especially during the final collapsing stage. When the bubble is far away from the edge, the bubble will be a nearly spherical one. 相似文献
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Vijay H Arakeri 《Pramana》1993,41(3):L291-L294
Influence of various gases on the intensity of single bubble sonoluminescence has been studied. The gases used were air, oxygen,
nitrogen, argon and helium. Among these oxygen gave the brightest intensity with nitrogen giving the least. 相似文献
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The numerical results obtained by Rayleigh-Plesset （R-P） equation failed to agree with the experimental Mie scattering data of a bubble in water without inappropriately increasing the shear viscosity and decreasing the surface tension coefficient. In this paper, a new equation proposed by the present authors （Qian and Xiao） is solved. Numerical solutions obtained by using the symbolic computation program from both the R-P equation and the Qian-Xiao （Q-X） equation clearly demonstrate that Q-X equation yields best results matching the experimental data （in expansion phase）. The numerical solutions of R-P equation also demonstrate the oscillation of a bubble in water depends strongly upon the surface tension and the shear viscosity coefficients as well as the amplitude of driving pressure, so that the uniqueness of the numerical solutions may be suspected if they are varied arbitrarily in order to fit the experimental data. If the bubble＇s vibration accompanies an energy loss such as the light radiation during the contract phase, the mechanism of the energy loss has to be taken into account. We suggest that by use of the bubble＇s vibration to investigate the state equations of aqueous solutions seem to be possible. We also believe that if one uses this equation instead of R-P equation to deal with the relevant problems such as the ＇phase diagrams for sonoluminescing bubbles＇, etc., some different results may be expected. 相似文献
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Numerical simulations for sonochemistry are reviewed including single-bubble sonochemistry, influence of ultrasonic frequency and bubble size, acoustic field, and sonochemical synthesis of nanoparticles. The theoretical model of bubble dynamics including the effect of non-equilibrium chemical reactions inside a bubble has been validated from the study of single-bubble sonochemistry. By the numerical simulations, it has been clarified that there is an optimum bubble temperature for the production of oxidants inside an air bubble such as OH radicals and H2O2 because at higher temperature oxidants are strongly consumed inside a bubble by oxidizing nitrogen. Unsolved problems are also discussed. 相似文献
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激光空泡在文丘里管中运动的动力学特性 总被引：1，自引：0，他引：1
以水为工作介质,在不同文丘里管入口压力下,利用YAG激光器产生的激光轰击水中的金属靶材产生空泡,借助高速摄像系统记录激光空泡在文丘里管中的运动过程,并采用流体动力学模拟对文丘里管中的流场特性和空泡的溃灭特性进行分析.结果表明:激光空泡在文丘里管中的运动,其形状变化可分为产生阶段、挤压阶段、溃灭初始阶段和溃灭阶段等四个阶段.空泡的溃灭取决于流场状态,当流动为层流时,空泡不发生溃灭;当流动为湍流时,空泡发生溃灭,且湍流程度越剧烈,溃灭现象越显著.搭建的激光空泡生成与运动系统能够实现空泡的定点溃灭. 相似文献
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Acoustic cavitation is a very important hydrodynamic phenomenon, and is often implicated in a myriad of industrial, medical, and daily living applications. In these applications, the effect mechanism of liquid surface tension on improving the efficiency of acoustic cavitation is a crucial concern for researchers. In this study, the effects of liquid surface tension on the dynamics of an ultrasonic driven bubble near a rigid wall, which could be the main mechanism of efficiency improvement in the applications of acoustic cavitation, were investigated at the microscale level. A synchronous high-speed microscopic imaging method was used to clearly record the temporary evolution of single acoustic cavitation bubble in the liquids with different surface tension. Meanwhile, the bubble dynamic characteristics, such as the position and time of bubble collapse, the size and stability of the bubbles, the speed of bubble boundaries and the micro-jets, were analyzed and compared. In the case of the single bubbles near a rigid wall, it was found that low surface tension reduces the stability of the bubbles in the liquid medium. Meanwhile, the bubbles collapse earlier and farther from the rigid wall in the liquids with lower surface tension. In addition, the surface tension has no significant influence on the speed of the first micro-jet, but it can substantially increase the speed of second and the third micro-jets after the first collapse of the bubble. These effects of liquid surface tension on the bubble dynamics can explain the mechanism of surfactants in numerous fields of acoustic cavitation for facilitating its optimization and application. 相似文献
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Bubble behaviors near a boundary in an ultrasonic field are the fundamental forms of acoustic cavitation and of substantial importance in various applications, such as industry cleaning, chemical engineering and food processing. The effects of two important factors that strongly affect the dynamics of a single acoustic cavitation bubble, namely, the initial bubble radius and the standoff distance, were investigated in this work. The temporal evolution of the bubble was recorded using high speed microphotography. Meanwhile, the time of bubble collapse and the characteristics of the liquid jets were analyzed. The results demonstrate that the intensity of the acoustic cavitation, which is characterized by the time of bubble collapse and the liquid jet speed, reaches the optimum level under suitable values of the initial bubble radius and the normalized standoff distance. As the initial bubble radius and the normalized standoff distance increase or decrease from the optimal values, the time of the bubble collapse increases, and the first liquid jet’s speed decreases substantially, whereas the speeds of the second and third liquid jets exhibit no substantial changes. These results on bubble dynamics in an ultrasonic field are important for identifying or correcting the mechanisms of acoustic cavitation and for facilitating its optimization and application. 相似文献
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A model for acoustic cavitation flows able to depict large geometries and time scales is proposed. It is based on the Euler–Lagrange approach incorporating a novel Helmholtz solver with a non-linear acoustic attenuation model. The method is able to depict a polydisperse bubble population, which may vary locally. The model is verified and analyzed in a setup with a large sonotrode. Influences of the initial void fraction and the population type are studied. The results show that the velocity is strongly influenced by these parameters. Furthermore, the largest bubbles determine the highest pressure amplitude reached in the domain, which corresponds to the Blake threshold of these bubbles. Additionally, a validation is performed with a small sonotrode. The model reproduces most of the experimentally observed phenomena. In the experiments, neighboring bubbles are found which move in different directions depending on their size. The numerical results show that the responsible mechanism here is the reversal of the primary Bjerknes force at a certain pressure amplitude. 相似文献
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《Ultrasonics sonochemistry》2014,21(3):1050-1064
This paper reports studies in ultrasound-assisted heterogeneous solid catalyzed (CaO) synthesis of biodiesel from crude Jatropha curcas oil. The synthesis has been carried out in two stages, viz. esterification and trans-esterification. The esterification process is not influenced by ultrasound. The transesterification process, however, shows marked enhancement with ultrasound. A statistical experimental design has been used to optimize the process conditions for the synthesis. XRD analysis confirms formation of Ca(OMe)2, which is the active catalyst for transesterification reaction. The optimum values of parameters for the highest yield of transesterification have been determined as follows: alcohol to oil molar ratio ≈ 11, catalyst concentration ≈ 5.5 wt.%, and temperature ≈ 64 °C. The activation energy of the reaction is calculated as 133.5 kJ/mol. The heterogeneity of the system increases mass transfer constraints resulting in approx. 4× increase in activation energy as compared to homogeneous alkali catalyzed system. It is also revealed that intense micro-convection induced by ultrasound enhances the mass transfer characteristics of the system with ∼20% reduction in activation energy, as compared to mechanically agitated systems. Influence of catalyst concentration and alcohol to oil molar ratio on the transesterification yield is inter-linked through formation of methoxy ions and their diffusion to the oil–alcohol interface, which in turn is determined by the volume fractions of the two phases in the reaction mixture. As a result, the highest transesterification yield is obtained at the moderate values of catalyst concentration and alcohol to oil molar ratio. 相似文献