Ultrasonic Cavitation Bubbles Kinetic Behavior

With the development of science and technology, the application of acoustic cavitation in the actual production increasingly broad and therefore is attracting much attention. In the study of bubble’s dynamical behavior, almost no analysis about the force on the bubble wall, and there is no reasonable explanation used to define whether the bubble collapse. In this paper, the analysis of the force on the bubble wall can not conclude when the bubble die out, but let us have new ideas and cognition about the process of bubble’s collapse to some extent.Using a spherical model of the bubble, the force on the infinitesimal plane of the bubble wall has been analyzed. According to the sources, the force on the bubble wall is divided into five component forces:the internal pressure (generated by bubble’s internal gas pressure), the external pressure (formed by hydrostatic pressure and ultrasound pressure), the surface tension, the viscous force and the radiation damping force (the reaction force generated by bubble’s vibration). And then each component of the force is solved by numerical calculation. By analyzing the correspondence between the component force and bubble radius under different physical parameters of solution and acoustic, reached following conclusions:(1) Whether the bubble collapse or not is affected by the initial size of the bubble radius. These bubbles can’t collapse which initial radius is too large or too small. If the bubble can collapse, the slightly oscillating portion gradually disappeared with the increasing of the initial bubble radius; if not, the bubble in a steady and periodically oscillation condition under the net force. The initial radius has a complex effect on bubble’s collapse. For different bubble with different initial radius, the component force’s value and role is different in bubble’s different phases. When the bubble compressed to collapse, the radiation damping force’s effect is more significant if the bubble can collapse.(2) With the increasing of the surface tension coefficient, the bubble’s slightly oscillating portion increasingly significant, when the surface tension coefficient increases to a certain value, the slight oscillation portion disappeared and the bubble in periodically stable oscillation. The surface tension coefficient is mainly affects the surface tension. The bubble will prematurely into the compression phase under the larger surface tension coefficient. This makes the external pressure can not play its major compression role at the right time. In addition, a longer time compression phase allows the internal pressure increased slowly, eventually hindered the bubble’s rebound.(3) With the increasing of the viscosity coefficient, the bubble’s slight oscillation part gradually disappeared. When the viscosity coefficient reaches to a certain value, the bubble tends to be stable oscillation. The viscous force plays a role of resistance effect which mainly associated with the viscosity coefficient. When the coefficient of viscosity increased, the viscous force’s effect is more significant. So the bubble’s expansion and compression phase were both suppressed, and eventually cause the bubble can’t collapse.(4) With the increasing of saturation vapor pressure, the slight oscillation portion of the bubble gradually disappeared. When the saturated vapor pressure increases to a certain value, the bubble’s radius keeps expanding. The internal pressure mainly associated with the internal pressure. When the saturation vapor pressure increases to a certain value, the bubble radius’change has a minimal impact on the internal pressure. For the relatively stable internal pressure, the net force periodically and sinusoidally with the time. The bubble expanded so large in the expansion phase, that there’s not enough time for the bubble to collapse in the compression phase.(5) If the sound frequency below the bubble’s resonance frequency, the bubble can collapse. As the sound frequency continues increasing, the bubble gradually tends to be stable oscillation. The sound frequency mainly affects the external pressure. The external pressure has a rapid change when the sound frequency increases to a certain value, which makes the bubble expansion and compression time is shorter, therefore there’s not enough time for the bubble to collapse.(6) The bubble’s expansion and compression is a dynamical process when there is difference between the inside and outside acting force. If the direction of the net force is in accordance with the positive direction set in this paper, the bubble expands. Otherwise, the bubble suppressed and compressed into the condensed phase. If the bubble can collapse, the direction of the surface tension and the internal pressure not changed, but the value changed instantaneously. The direction and the value of the viscous force and the radiation damping force both changed instantaneously.