Papers by Keyword: Acoustic Cavitation

Abstract: Megasonic cleaning is one of the promising technologies to remove the particles during semiconductor processing. Acoustic bubble cavitation plays a key role in removing the particles. In this work, the effect of an anionic surfactant sodium dodecyl sulfate (SDS) on a bubble in the presence of hydrogen dissolved DIW water was studied. The bubble dynamics were observed using a high-speed camera. It was found that with the increase of surfactant the bubble characteristics were changed very significantly. Several parameters affecting the bubble dynamics were investigated.

Abstract: Visualization experiments were performed to study the relation between free-surface motion and bubble translation in a 1-MHz ultrasonic cleaning bath. From the visualization with a video camera, the characteristic frequencies of the free-surface oscillation (under the acoustic radiation force) and the translational velocity of cavitation bubbles (trapped via the primary Bjerknes force) were extracted, showing that there is a strong correlation between the free-surface oscillation and bubble translation. From the context of megasonic cleaning, such free-surface oscillation is expected to contribute to uniform cleaning performance with cavitation bubbles.

Abstract: Visualization experiments were performed to examine whether acoustic bubbles play a role in ultrasonic water flow cleaning, as in convention cleaning with ultrasonic baths. Schlieren visualization confirmed the standing-wave-like acoustic field in ultrasonic water flow that collides with a glass surface. Backlight visualization showed that cavitation bubbles appear in the water flow spreading over the glass surface. These bubbles are found to oscillate in volume and move inside film flow and thus expected to play a role as active cleaning agents.

Abstract: Problems of transforming heavy crude high-sulfur oil into low-sulfur fuels and oils become increasingly urgent for oil refineries. The main reason for that is depletion of low-sulfur oil-fields and following rise of heavy crude oil share in world's oil production. Desulfurization of oil and petroleum residues is performed by breaking down or extraction of sulfur and sulfur compounds with catalyst and chemical additives which leads to considerable rise in price of refinery. Desulfurization technology proposed in the following research involves simultaneous use of the acoustic and hydrodynamical cavitation for breaking down long molecular connections. Oil refinery was performed in the electromechanical vortex layer activator which intensified mechanoactivation processes by intensive movement of ferromagnetic elements in the external magnetic field.

Abstract: Put forward an application of ultrasonic cavitation technology of the sewage source heat pump system to solve the problem of controlling pollution and emphatically discusses the principle of acoustic cavitation and the effect, to conduct a feasibility analysis of Anti-fouling in sewage source heat pump sewage side. Through analysis principle of ultrasonic cavitation and heat transfer enhancement for carrying the experiment, study the pattern of scaling in heat exchange tube for different velocity and viscosity, effect in flow rate on the ultrasonic cleaning wastewater, Effect in ultrasonic treatment time on the descaling result. Obtain that it can enhancement transfer for 48%.

Abstract: The motion characteristic of cavitation bubble is one of the major factors affecting acoustic cavitation. In this paper, a cavitation model coupled with acoustic pressure is established using lattice Boltzmann pseudopotential model. Aimed at demonstrating the feasibility of applying LB method in acoustic cavitation, the acoustic cavitation simulations are compared with the predictions of Keller equation. The comparison of theoretical prediction and numerical simulation shows that LB method is suitable for acoustic cavitation simulation.

Abstract: Removal of particulate residues represents a very challenging step in current CMOS-technology nodes. The continued miniaturization and the introduction of novel materials in the semiconductor industry have resulted in very stringent requirements for device fabrication steps such as cleaning processes [. Physical forces, acting directly on the surface to be cleaned, are currently employed for delicate particle removal as an alternative to more aggressive chemistries [2]. High frequency ultrasounds (500 kHz 4 MHz), or megasonics, rely on the action of oscillating bubbles created during the ultrasonic agitation of the cleaning liquid. Strongly oscillating gas bubbles are able to generate shear forces, which are considered to be responsible for cleaning [3]. However, collapsing bubbles close to a surface can also produce water jets and shockwaves which lead to damage of fragile structures. Fundamental research is needed in order to overcome these issues by improving the understanding of the physical parameters playing a role in the acoustic cavitation of bubbles. This study reports the effects of lowering the surface tension of the liquid bulk on the bubble activity in the MHz range. A lower surface tension (45 mN/m) with respect to water (72 mN/m) is obtained by adding a non-ionic surface-active agent (TritonX-100). After fully characterizing its wettability, a cleaning solution containing surfactant is investigated under pulsed and continuous acoustic fields, for different acoustic amplitudes and gas concentrations. The aim is to increase bubble activity while reducing the strength of the bubble collapse. The results obtained can be useful in tuning megasonic cleaning systems towards more efficient processes.

Abstract: An important problem in megasonic cleaning is the nucleation process of bubbles, which act as the cleaning agents. A fundamental understanding of this nucleation process will help to optimize the cleaning parameters for future applications to achieve damage free cleaning. In this work, we use quantitative stroboscopic Schlieren imaging to study the interaction of nucleating bubbles with a travelling acoustic wave. The advantage of this method is that it is non-interfering, meaning that it does not disturb the bubble nucleation. It is revealed that nucleation mechanism is a 2 step process, where a regime of slow bubble growth due to rectified diffusion is subsequently followed by a transient cavitation cycle, where bubbles grow explosively. The latter is accompanied by broadband acoustic emission and enhanced thermal dissipation, leading to the occurrence of thermal convection visible in the Schlieren images.

Abstract: Ultrasonic vibration has been applied to various molten metal processes owing to the functions of (a) improvement in wettability, (b) liquid adhesion at a vibrating end surface and (c) sono-solidification such as grain refinement. The present study is focused on the sono-solidification with acoustic cavitaion in hypereutectic Al-18mass%Si alloy. There appears an equilibrium microstructure composed of primary silicon and coupled eutectic -Al/Si phases in Al-18mass%Si alloy, however, non-equilibrium -Al grains develop along with the equilibrium phases through the sono-solidification. During the sono-solidification of Al-18mass%Si alloy, non-equilibrium -Al grains are recognized in the molten metal close to the ultrasonic radiator just before reaching the eutectic temperature of 577 oC in addition to the refined primary silicon particles. The appearance of -Al grains is understood through acoustic cavitation: ultrasound in molten Al-Si alloys exhibits two outstanding behaviors of cavitation bubbling and acoustic streaming. Firstly the de-coupled eutectic reaction, which is recognized in the solidified eutectic Al-Si alloy with severe stirring, causes divorced -Al grains by the acoustic streaming with cavitation. Secondly it is expected that high pressure of over 1 GPa generated by the collapse of cavitaion babbles leads to not only an increase in the eutectic temperature, but also higher silicon content at the eutectic point in Al-Si alloy. Consequently, non-equilibrium -Al grains are nucleated at collapsed cavitaion bubble sites, and they are characterized by higher silicon content compared with that of primary -Al grains in hypoeutectic Al-7masst%Si alloy.

Abstract: Ultrasonic irradiation during the solidification of molten metals has an effect on grain refinement. However, the mechanism of grain refinement by ultrasonic vibration has not been fully understood yet, so that there exist difficulties to apply the ultrasonic grain refinement to industrial casting processes. In the present study, we propose the mechanism of ultrasonic grain refinement: the nucleation is based on the extremely high pressure generated by the collapse of acoustic cavitation in molten Al-Si alloys. The effect of ultrasonic irradiation into molten Al-Si alloy on the microstructure was firstly studied, that is, molten Al-12.6wt%Si alloy was rapidly cooled down from just above the eutectic temperature after the ultrasonic irradiation. The detailed microstructure observation exhibits that ultrasonic irradiation above the eutectic temperature causes crystalline -Al and silicon to nucleate. Through the measurement of silicon content in -Al nodules solidified with ultrasonic irradiation, the silicon content is higher than that in non-irradiated -Al nodules. It is known that the collapse of acoustic cavitation generates extremely high pressure. At the highly pressurized sites, the eutectic temperature rises and the crystallized -Al nodules contain higher amount of silicon compared with those solidified at ambient pressure. According to the fact that the -Al nodules crystallized above the eutectic temperature contain higher amount of silicon, the irradiated microstructure of -Al nodules is developed at the highly pressurized sites, that is, the collapse of acoustic cavitation induces nucleation and causes grain refinement.