Numerical simulation of cavitation-induced bubble dynamics near a solid surface

Acoustic cavitation is a process in which bubbles are nucleated and oscillating in an acoustic field. When such bubbles collapse near a solid surface, the interaction of the resulting shock waves and micro-jets with the solid surface can be engineered for a number of applications, like surface cleaning in microelectronics, sonoporation in biomedical applications, and improvements in steel pickling performance in the metallurgical industries. Unfortunately, it is experimentally quite challenging to study such cavitation-induced bubble dynamics due to the randomness of the phenomenon and the associated small time and length scales. In this work, we have simulated both shock wave emission during the collapse of a spherical bubble, and jet penetration during aspherical bubble collapse near a solid surface. As to the first part, the propagation of shock waves in the liquid has been simulated combining the Gilmore model and the method of characteristics. Simulations have shown that shock waves can be responsible for structural damage observed during acoustic cavitation-induced cleaning in microelectronics. In a second part, the collapse of a bubble near a solid surface has been simulated by a two-phase flow model. In this model, the Navier-Stokes equations are solved on a Cartesian mesh and the interface is represented and tracked by the Volume Of Fluid method. The main advantage of this approach is that it allows to take into account the liquid viscosity in the numerical model. Our simulations have shown that the evolution of the bubble shape with time is in good agreement with experimentally observed laser-induced bubble dynamics. Using this model, simulations of laser-induced and acoustic-induced bubble dynamics have been carried out.(FSA 3) -- UCL, 201

Modeling of shock wave emission during acoustically-driven cavitation-induced cleaning process

Shock wave emission resulting from spherical bubble collapse during cavitation-induced cleaning process on Si wafers is modelled. The velocity of the shock front is calculated as a function of cavitation process parameters and gas state equations.Anglai

Réflexions sur les règles de répartition des compétences lors de la crise du coronavirus Covid-19

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La responsabilité personnelle des Directeurs généraux, avec ou sans délégation

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Audition sur les tests de situation

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Les rendez-vous manqués de la laïcité

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Shock wave emission upon spherical bubble collapse during cavitation-induced megasonic surface cleaning.

When a gas bubble in a liquid interacts with an acoustic wave near a solid surface, the bubble first expands and then collapses. In this paper, a mathematical framework combining the Gilmore model and the method of characteristics is presented to model the shock wave emitted at the end of the bubble collapse. It allows to describe the liquid velocity at the shock front as a function of the radial distance to the bubble center in the case of spherical bubble collapse. Numerical calculations of the liquid velocity at the shock front have shown that this velocity increases with the acoustic amplitude and goes through a maximum as a function of the initial bubble radius. Calculations for different gas state equations inside the bubble show that the Van der Waals law predicts a slightly higher liquid velocity at the shock front than when considering a perfect gas law. Finally, decreasing the value of the surface tension at the bubble/liquid interface results in an increase of the liquid velocity at the shock front. Our calculations indicate that the strength of the shock waves emitted upon spherical bubble collapse can cause delamination of typical device structures used in microelectronics

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