Theoretical Research On Ultrasonic Cavitation And Simulation Analysis Of Affecting Factors

With the development of science and technology, ultrasonic cavitation has been widely used in more and more fields. Under the action of ultrasound, gas nucleus in a liquid medium generates the phenomenon of ultrasonic cavitation. As these bubbles collapse, extreme physical and chemical conditions of thousands of degrees and thousands of atmospheres are generated within the bubble. Intense shock waves are launched outwards from the imploded bubble at velocities exceeding the speed of sound. By controlling the ultrasonic cavitation occurrence and the cavitation intensity, we can achieve some purposes which are not in general conditions. Since the movement of cavitation bubble is highly non-linear, and its movement cycle is short, it will be difficult to measure it in experiments. From the theoretical basis, this paper adopts the method of numerical analysis to analyze ultrasonic cavitation.This paper is mainly based on slight modifications of the Kyuichi Yasui model, which considerate the liquid compressibility, the liquid viscosity, the surface tension, the radiation damping, and the evaporation and condensation of water vapor, to build dynamic equation of cavitation bubbles. Using MATLAB to solve those above dynamics equation of ultrasonic cavitation bubble, we obtain the radius of ultrasonic cavitation bubble, the temperature and the pressure within the bubble, the number of water vapor molecules, the internal energy, and the total kinetic energy of all gas molecules. By comparing the cavitation bubble dynamics models with or without considering the evaporation and condensation of water vapor, we conclude that though the evaporation and condensation of water vapor has a little effect on the cavitation bubble radius, it has great impact on the other state parameters, such as the temperature and the pressure within bubbles, thus cannot be neglected.Based on the ultrasonic cavitation kinetic equation, by changing elements which have influence on ultrasonic cavitation like the initial radius of the cavitation bubble, the ultrasonic frequency, the ultrasonic amplitude, the liquid viscosity, the surface tension and the temperature of liquid medium, we study these elements’influence on ultrasonic cavitation.Ⅰ. By changing the initial radius of the cavitation bubble, and also consequently changing the number of gas molecules within the bubble, we conclude that the size of the initial radius of the cavitation bubble has little impact on the radius and movement of cavitation bubble. Because of the increased initial number of molecules within the bubble, the number of molecules of water vapor, the internal energy and the total kinetic energy of the gas molecules within the bubble correspondingly increase.Ⅱ. By changing the frequency of the ultrasonic wave, we reach the conclusion that the higher the frequency of the ultrasonic wave is, the smaller the radius of the cavitation bubble is. Besides, the temperature and pressure within the bubble decrease in a limited extent, and the number of water vapor molecules, the internal energy, the total kinetic energy of the gas molecules within the bubble decline in a larger extent.Ⅲ. By changing the amplitude of the ultrasonic wave, we conclude that the greater the amplitude of the ultrasonic wave is, the greater the radius of the cavitation bubble, and the temperature, the pressure, the number of water vapor molecules, the internal energy, the total kinetic energy of the gas molecules within the bubble are, and in an obvious extent.Ⅳ. By changing the viscosity of the liquid medium, we conclude that the greater the viscosity of the liquid is, the smaller the radius of the cavitation bubble, and the temperature, the pressure, the number of water vapor molecules, the internal energy, the total kinetic energy of the gas molecules within the bubble are. In addition, with the increase of liquid viscosity, the impact on the movement of the cavitation bubble becomes greater, even makes the cavitation bubble remain in steady oscillation.Ⅴ. By changing the surface tension of the liquid medium, we conclude that the greater the surface tension is, the smaller the radius of the cavitation bubble, and the temperature, the pressure, the number of water vapor molecules, the internal energy, the total kinetic energy of the gas molecules within the bubble are. But it has little effect on ultrasonic cavitation within the normal range.Ⅵ. By changing the temperature of the liquid medium, we conclude that the higher the temperature of the liquid medium is, the larger the radius of the cavitation bubble is. Besides, the maximum temperature and the maximum pressure within the bubble decrease significantly, and the minimum pressure, the number of water vapor molecules, the internal energy, the total kinetic energy of the gas molecules within the bubble increase substantially.