A Quantitative Study On The Collapse Mechanics Of Acoustic Cavitation Bubbles

Ultrasonic cavitation is a complex physical phenomenon.When the liquid is subjected to a certain power of ultrasound,tiny cavitation bubbles will be generated inside it.When the cavitation bubble collapses near the wall,the micro-jet generated will generate a greater pressure on the solid wall.For example,in the ultrasonic assisted welding process,the micro-jet mainly relies on the action of the micro-jet to remove the oxide film on the surface of the base material,so ultrasonic cavitation It is widely used in wastewater treatment,biomedicine and industrial production.In order to measure the mechanical effects of cavitation bubbles at the liquid/solid interface,this paper uses the latest dynamic high-frequency piezoelectric quartz sensor to measure the force when the cavitation bubbles collapse,and uses COMSOL Multiphysics simulation software to extend the experiment.Expand to calculate the distribution of the sound pressure field under different conditions to calculate the pressure near the bubble wall when the cavitation bubble collapses under different conditions with the help of Matlab.Through the distribution of cavitation bubbles at the liquid/solid interface observed by the high-speed photography system,calculate the force and pressure acting on the near wall when a single cavitation bubble collapses at the liquid/solid interface where the liquid metal is in contact with the quartz glass.Through the dynamic high frequency piezoelectric quartz sensor,it is found that the force that affects the collapse of the cavitation bubble is mainly related to the type of liquid,the position,and the size of the ultrasonic power.On the premise that the other experimental conditions are the same,the smaller the viscosity of the liquid,the greater the collapse of the cavitation bubble.Under the condition of large-scale liquid and limited area,the cavitation bubble collapse force in the area directly below the ultrasonic head is significantly higher than that on the side;in the state of free surface,the cavitation force at the position far from the ultrasonic head is the largest,and the cavitation force is at the middle position The smallest.As the ultrasonic power increases,the force when the cavitation bubble collapses also increases.In the COMSOL simulation results,it is simulated and verified that the type,location,ultrasonic power and frequency of the liquid are important factors that affect the sound pressure.Under large-scale liquid conditions,the sound pressure contour is distributed in an arc shape with the center of the lower surface of the ultrasonic head applying vibration as the center,and the sound pressure is diffused and attenuated outward;under limited area conditions,the glass bottom plate reflects part of the sound The sound field is superimposed under the ultrasonic head,which changes the distribution of the sound pressure field.It is further found that the ultrasonic frequency can change the positive and negative distribution of the sound pressure field and the size of the sound pressure value,and the structure of the extremely thin solder layer is beneficial to amplify the sound pressure.Matlab uses the sound pressure amplitude obtained by simulation to calculate the pressure when the cavitation bubble collapses,and its order of magnitude is 10⁹-10¹¹ Pa.For the study of cavitation bubble distribution,cavitation bubbles in water are mostly produced in the form of clusters under limited area conditions but the distribution is not uniform.The area and density of cavitation bubbles in ethanol are far less than those in water.On the side of the ultrasonic head,the formation and disappearance of cavitation bubble clusters and cloud structures require more ultrasonic cycles.As the ultrasonic power increases,the area of the cavitation area becomes larger,and the degree of cavitation becomes more severe.Under the condition of the free surface of the solder pool,as the ultrasonic power increases,the area of the cavitation area increases significantly,and the cavitation bubbles are smaller and denser and appear in the form of clusters.Under the action of the ultrasonic power of 1000 W,about 40.6 cavitation bubbles are collapsed in each ultrasonic cycle of the 4 mm² field of view,and the area occupied by the cavitation bubbles is about 1.5%.The average value of the collapse force of a single cavitation bubble at the metal liquid/solid interface is about 5-10 m N,and the average pressure of the microjet on the solid wall caused by the collapse of the cavitation bubble is about 100-400 MPa.