Study On The Breaking Behavior And Mechanism Of Suspended Bubbles In Free Space

The occurrence,expansion,coagulation and fragmentation of bubbles can be seen everywhere in life,and they are also commonly found in industrial equipment involving gas-liquid two-phase flow such as evaporators,two-phase reactors,and medium atomizers.In a two-phase flow system,the gas is usually dispersed into the liquid in the form of bubbles.The formation,development and fragmentation of the bubbles are important parameters affecting the gas-liquid two-phase flow.For example,in the bubble atomization process,the breakage of the bubbles is beneficial to reduce the average diameter of the particles and enhance the evaporation of the liquid mist,and the bubble breakage in the boiler steam drum can increase the water volume of the steam and reduce the working efficiency.Therefore,the related research on bubble breaking has certain practical significance and engineering value.In this paper,the experimental method is used to explore the breaking process and behavioral phenomena of suspended bubbles in free space.The high-speed camera is used to capture the bubble breaking process.Bubble breakage in free space is divided into four processes: draining,forming holes,liquid film curling,and jetting.The time required for the draining process is defined as the "bubble life" of the natural collapse of the bubble,which is related to the mass and size of bubbles.In the hole forming process,the position of the initial break point of the bubble in the free space appears randomly,and the top probability is the largest.In the process of liquid film curled,the surface liquid film exhibits a radial shrinkage phenomenon,and the shrinkage is more obvious as the radius of curvature of the bubble decreases.During the jet process,the liquid film shrinks into a mass,and the focusing effect causes the remaining liquid film to be ejected toward the initial fracture point.The process of bubble breaking is a complex non-stable and unstable development process,which shows different laws under different environmental conditions and liquid film properties,and it is affected by many factors such as solution surface tension coefficient,viscosity,bubble size and liquid film thickness.The larger the surface tension coefficient of the bubble blowing solution is,the shorter the liquid discharge time is,the more uniform the liquid film thickness is,and the more obvious the jet flow at the end ofthe crushing is.the larger the viscosity of the solution is,the less likely the bubble is formed,and the smaller the number of film droplets during the crimping process is,the more difficult to form a jet.the larger the initial diameter of the bubble is,the smaller the average curl rate is,the more the number of film droplets formed,the wider the spatial distribution of the film droplets is.As the thickness of the liquid film increases,the edge liquid film curls for a longer period of time,and more droplets are formed by the liquid line breakage.The theoretical method is used to investigate the overall stress before and after the bubble is broken.During the bubble breaking process,the overall deformation of the semi-closed curved liquid film is the result of the change of the force.Based on mass conservation,momentum conservation and energy conservation,we study the edge liquid film curling characteristics of liquid film.The local thinning of the liquid film thickness caused by the discharge process of suspended bubbles is the main reason for the increase of the curling angular velocity of the liquid film in the initial stage of bubble breaking.In the stage of disturbance wave delay,the edge liquid film accumulation and mass increase lead to a gradual decrease of the curl angular velocity.In the membrane droplet separation stage,the edge liquid film curl angular velocity remains basically unchanged,and the surface potential energy of broken liquid film is mainly converted into separation kinetic energy of droplets and tangential/radial kinetic energy of edge liquid film.In this paper the research results not only can enrich the understanding of the law and mechanism of bubble breaking behavior,but also have certain guiding significance for solving practical problems in related projects.