Effect of ultrasonically induced cavitation on inhibition behavior of polyethylene glycol on carbon steel corrosion

In this investigation the influence of 24 kHz ultrasound wave upon the corrosion of carbon steel in 3N sulphuric acid at 25 degrees C in the presence of inhibitors was studied. The inhibitors were polyethylene glycols (PEG) in different molecular weights (from 400 up to 10,000 gmol(-1)). The polarization and impedance spectroscopy results show the effectiveness of polyethylene glycols on the cavitation-corrosion inhibition of carbon steel in sulphuric acid. The inhibition efficiency is increased with increasing mean molecular weight of polymer and its concentration. The weight loss method has confirmed these results. The analysis of SEM images indicates that these inhibitors prevent propagation of pits on the eroded specimen. The inhibition effect of PEGs can be attributed to cushioning effect of adsorbed polymers on cavitation phenomenon produced by bubble collapse.     

Dependence of wetting on cavitation during the spreading of a filler droplet on the ultrasonically agitated Al substrate

The cavitation characteristics during the spreading of a pure Sn liquid droplet subjected to ultrasonication were studied for the first time through high-speed photography to reveal the wetting mechanism. Ultrasonic vibration realized the spreading of Sn droplet on the nonwetting pure Al substrate. However, the oxide layer of the substrate at the spreading front is difficult to remove. The high-speed photography result shows that a noncavitation region consistently appears at the spreading front, because the acoustic pressure is below the cavitation threshold of 1.26 MPa. In particular, the width of the noncavitation region gradually increases as the size of the spreading area increases. Such a result accounts for the condition wherein the oxide layer at the spreading front is difficult to remove. Furthermore, the bubble density during spreading gradually decreases due to the decreased acoustic pressure of the thinned liquid. Finally, the bubble dynamics were calculated to verify the wetting mechanism.     

圆柱体的空间圆锥光反射、折射与衍射

用准直或会聚激光束倾斜照射圆柱体时,其反射光、透射光(柱体透明时)、衍射光(柱体较细时)的叠加将形成以光束入射点为顶点的空间圆锥形光面(空间光锥),并且在垂直于柱体轴线方向的观察平面上投影成一圆形光环.空间光锥的形成与所选圆柱体材料及其粗细无关,只要其表面具有一定反射能力即可.空间光锥的锥角等于入射光束主光轴与圆柱体轴线夹角的2倍,与圆柱体和照射光束的直径大小及光波长无关.给出了对光纤及不同直径大小的玻璃和金属圆柱体的实验观察结果,并利用矢量图解法对其进行了详细地理论分析.进而得出,通常所谓单丝衍射图样,实际上是细丝的衍射和其表面的反射光场的叠加图样,对于透明细丝,还包括其透射光场的贡献.圆柱体的这种空间圆锥光反射和衍射原理有可能用于光束定位、成形、表面检测以及三维面形测量等 关键词： 圆柱体 空间光锥 投影光环     

超声空化引起界面湍动促进的传质机理

本文分析了超声空化引起界面湍动对传质过程的影响,提出了相界面上超声空化气泡析出增强边界层液体湍动并促进传质的机理,在传质理论和流体动力学原理的基础上,建立了超声空化引起界面湍动促进的传质机理模型,获得了超声空化引起界面湍动促进的传质系数表达式。实验结果验证了模型的合理性。该模型既证实了超声对传质有强化效应,又对传质过程有很好的预测功能,为工业化提供了理论依据。     

Force acting on an atom and a classical oscillator in an electromagnetic field

The expression for the force exerted by the field on an atom and averaged over the field period is derived in quantum-mechanical perturbation theory, in which a quasi-monochromatic electromagnetic field plays the role of a perturbation. An approximate solution is obtained to the classical (Newton) equation of motion in the same field for a harmonic isotropic oscillator. In both problems, the expressions for the force acting on a particle are completely identical if they are written in terms of the polarizability (of the atom and the oscillator). These results conform with the data obtained in macroscopic electrodynamics for rarefied media.     

Force response of a viscous liquid in a probe-tack geometry: Fingering versus cavitation

We perform traction experiments on viscous liquids highly confined between parallel plates, a geometry known as the probe-tack test in the adhesion community. Direct observation during the experiment coupled to force measurement shows the existence of several mechanisms for releasing the stress: while fingering is favored for low traction velocities, low confinement and low viscosity, nucleation of bubbles occurs in the opposite conditions. It is possible to quantitatively predict the transition between the two regimes and, in many respects, describe the shape of the force response. Using a model for purely viscous fluids, we also present a phase diagram for the different force peak regimes that remarkably accounts for the data. Our results show that conspicuous features of the traction curve commonly thought to be characteristic of soft viscoelastic solids like adhesives are already encountered in liquid materials.Received: 30 July 2004, Published online: 26 October 2004PACS: 82.35.Gh Polymers on surfaces; adhesion - 47.55.Bx Cavitation - 83.50.Jf Extensional flow and combined shear and extension     

Enhancement of ultrasonically induced cell damage by phthalocyanines in vitro

In this work, erythrocytes from carp were used as a nucleated cell model to test the hypothesis that the phthalocyanines (zinc - ZnPc and chloroaluminium -AlClPc) enhance ultrasonically induced damage in vitro. In order to confirm and complete our earlier investigation, the influence of ultrasound (US) and phthalocyanines (Pcs) on unresearched cellular components, was studied. Red blood cells were exposed to 1 MHz continuous ultrasound wave (0.61 and/or 2.44 W/cm²) in the presence or absence of phthalocyanines (3 μM). To identify target cell damage, we studied hemolysis, membrane fluidity and morphology of erythrocytes. To demonstrate the changes in the fluidity of plasma membrane we used the spectrofluorimetric methods using two fluorescence probes: 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5,-hexatriene (TMA-DPH) and 1,6-diphenyl-1,3,5-hexatriene (DPH). The effect of US and Pcs on nucleated erythrocytes morphology was estimated on the basis of microscopic observation.The enhancement of ultrasonically induced membrane damage by both phthalocyanines was observed in case of hemolysis, and membrane surface fluidity, in comparison to ultrasound. The authors also observed changes in the morphology of erythrocytes. The obtained results support the hypothesis that the Pcs enhance ultrasonically induced cell damage in vitro.Furthermore, the influence of ultrasound on phthalocyanines (Pcs) in medium and in cells was tested. The authors observed changes in the phthalocyanines absorption spectra in the medium and the increase in the intensity of phthalocyanines fluorescence in the cells. These data can suggest changes in the structure of phthalocyanines after ultrasound action.     

Acoustic cavitation induced by ultrasonic cutting devices: a preliminary study

Ultrasonic cutting is frequently used for the separation of foods, especially in case of commodities with multiple layers showing a different mechanical resistance. Both chemiluminescence measurements and the degradation of organochloric compounds served as an evidence for the occurrence of acoustic cavitation around excited cutting blades. Additionally, sensory experiments revealed that even a short ultrasonic treatment of edible oil is sufficient to generate a remarkable off-flavor.     

A high-temperature acoustic field measurement and analysis system for determining cavitation intensity in ultrasonically solidified metallic alloys

A high-temperature acoustic field measurement and analysis system (HTAFS) was self-designed and developed to achieve real-time acoustic field analysis and quantitative cavitation characterization within high-temperature liquids. The acoustic signal was acquired by a high-temperature resistant waveguide and calibrated by separate compensation of line and continuous spectra to eliminate frequency offsets. Moreover, a new method was proposed to derive from the continuous-spectrum sound intensity and line-spectrum sound intensity in the frequency band above 1.5 times the fundamental frequency to characterize the intensity of transient cavitation and stable cavitation. The acoustic field characteristics within solidifying liquid Al-7 %Si alloy were successfully determined by this system. With the increase of ultrasound amplitude, the acoustic pressure in the alloy melt increased to be stable, the transient cavitation intensity first rose and then declined, and the stable cavitation intensity remained unchanged. Combined with the structural evolution of the primary α(Al) phase, the transient cavitation intensity was determined to be the dominant factor for the ultrasound-induced grain refinement effect.     

Two-dimensional diffraction on a cylinder induced by a laser beam in a nonlinear gradient medium

A wave theory was developed and a numerical simulation performed of the diffractive flow of a signal wave around a negative inhomogeneity induced by a cylindrical pump beam in nonlinear medium while keeping both waves in the potential well. It was shown that a broad pump beam reflects a narrow signal beam. A nonlinear waveguide (a dark soliton) is described as well. These phenomena can be observed in Bose-Einstein condensate (BEC) and in a gradient waveguide.     

Sonochemical and high-speed optical characterization of cavitation generated by an ultrasonically oscillating dental file in root canal models

Ultrasonically Activated Irrigation makes use of an ultrasonically oscillating file in order to improve the cleaning of the root canal during a root canal treatment. Cavitation has been associated with these oscillating files, but the nature and characteristics of the cavitating bubbles were not yet fully elucidated. Using sensitive equipment, the sonoluminescence (SL) and sonochemiluminescence (SCL) around these files have been measured in this study, showing that cavitation occurs even at very low power settings. Luminol photography and high-speed visualizations provided information on the spatial and temporal distribution of the cavitation bubbles. A large bubble cloud was observed at the tip of the files, but this was found not to contribute to SCL. Rather, smaller, individual bubbles observed at antinodes of the oscillating file with a smaller amplitude were leading to SCL. Confinements of the size of bovine and human root canals increased the amount of SL and SCL. The root canal models also showed the occurrence of air entrainment, resulting in the generation of stable bubbles, and of droplets, near the air–liquid interface and leading eventually to a loss of the liquid.     

Effects of roughness elements on bypass transition induced by a circular cylinder wake

Abstract  

The bypass transition of flat-plate boundary layer induced by a circular cylinder wake under the influence of roughness elements is experimentally investigated. The hydrogen-bubble visualization results show that the boundary layer separation occurs upstream of the roughness, and the separated shear layer is incised by roughness to different extent, resulting in different kinds of secondary vortices formed immediately downstream of the roughness. During the evolution of the secondary vortex, two types of instabilities are observed, which are denoted as large- and small-scale instabilities, respectively, according to different spatial scale of the hairpin vortices formed afterward. A merging process of hairpin vortices is also observed when the secondary vortices undergo the small-scale instability, and a potential new transition control strategy based on the present observation is proposed.     

Grain refinement caused by intensified cavitation within narrow channel and its improvement to ultrasonically soldered Al joint property

In this work, grain refinement of the aluminum soldered joint was obtained by applying cavitation within narrow channels and the possible grain refinement mechanism was proposed. Aluminum sheets with different channel widths were ultrasonically soldered by pure Sn in air. An ultrasonic system with a TC4 sonotrode, was operated at a frequency of 20 kHz and power of 1000 W during soldering. The effect of channel width on grain size, element distribution and strength of the soldered joint was studied. Results showed that the grain size decreased from 2.62 to 1.04 µm and the element ratio of Al in solder increased from 0.93 to 4.86% when the channel width decreased from 0.8 to 0.2 mm. Instant solidification of Sn grains was readily observed in the joint before cooling due to the large undercooling induced by the intensified cavitation inside the narrow channels. The random cavitation induced nucleation of Sn was believed to be mainly responsible for the grain refinement of the soldered joint. The shear strength of the joint increased from 29.5 to 48.8 MPa and the hardness increased from 16.5 to 25.2 HV due to the grain refinement of Sn and the presence of Al transferred from the substrates.     

Effect of exposure parameters on cavitation induced by low-level dual-frequency ultrasound

In order to quantify the effects of exposure parameters under therapeutic conditions such as sonodynamic therapy, it is necessary initially to evaluate the inertial cavitation activity in vitro. In this study, the dependence of cavitation activity induced by the low-level dual-frequency ultrasound irradiation on exposure parameters has been studied. Experiments were performed in the near 150 kHz and 1 MHz fields in the progressive wave mode. It has been shown that at constant ultrasound energy the fluorescence intensity for continuous sonication is higher than for pulsed mode. With increasing the duty cycle of pulsed field, the inertial cavitation activity is increased. The activity of cavitation produced by simultaneous combined sonication by two ultrasound fields is remarkably higher than the algebraic sum of effects produced by fields separately (p-value < 0.05). This study shows that simultaneous combined dual-frequency ultrasound sonication in continuous mode is more effective in producing inertial cavitation activity at low-level intensity. Therefore, it is concluded that investigations in this combined ultrasound sonication can be useful in sonodynamic therapy for superficial tumors.     

Large eddy simulation of a shocked gas cylinder instability induced turbulence

The Navier-Stokes equations for compressible fluid are solved with the operator splitting technique and LES (large eddy simulation) with the Smagorinsky model. A computational code MVFT (multi-viscosity-fluid and turbulence) is developed to study hydrodynamic instability and the induced turbulent mixing for multi compressible fluid. In order to validate the code MVFT,the LANL's shock tube experiment of shocked SF6 gas cylinder is simulated with the initial state of SF6 gas cylinder described by dissipative ...     

Effect of picosecond laser induced cavitation bubbles generated on Au targets in a nanoparticle production set-up

This work is aimed at an analysis of the influence on the efficiency of nanoparticle production of a cavitation bubble (CB), which forms during the laser ablation process in high-fluence regime. The CB is produced on an Au metal target immersed in water by 1064 nm ps Nd:YAG laser pulses at different fluences. Its time–space evolution is monitored by a shadowgraphic set-up, while the Au nanoparticles production rate is tagged by the growth of the plasmon resonance, which is detected by measuring shot-by-shot the UV-Vis absorbance. We analyze the dependence of bubble size on the experimental parameters. Our results appear of interest to enhance the nanoparticle production efficiency in a liquid medium.     

Sonoelectrochemical and sonochemical effects of cavitation: correlation with interfacial cavitation induced by 20 kHz ultrasound

Sonoelectrochemical measurements at macro-electrodes under extreme conditions with a very short distance between ultrasonic horn tip and electrode and different ultrasound intensity levels are shown to result in violent cavitation detected in form of current peaks superimposed on the average limiting current. Analysis of the current data obtained for the oxidation of ferrocene in dimethylformamide (0.1 M NBu4PF6) at a 4 mm diameter Pt disc electrode and for the reduction of Ru(NH3)6(3+) in aqueous 0.1 M KCl at a 6 mm diameter Pt disc electrode consistently indicate a change of the physicochemical nature of sonoelectrochemical processes under extreme conditions. The sonoelectrochemical measurement of the rate constant for the carbon bromide bond cleavage of a 3-bromobenzophenone radical anion electrogenerated at a glassy carbon electrode in dimethylformamide solution in the presence of power ultrasound is shown to yield evidence for a breakdown of the conventional mass transport model of a planar diffusion layer under extreme conditions. The change can be correlated to the number of current data points deviating more than 10% from the mean of the current due to violent cavitation processes superimposed onto the average limiting current. Further, a study of the sonochemical destruction of aqueous dilute cyanide solution (in 0.1 M NaOH) demonstrates a correlation between the electrochemically detected cavitation violence and the sonochemical activity. Factors that govern the violence of interfacial cavitation appear to be directly proportional to the factors that make cavitation in the bulk solution chemically efficient.