Numerical Simulation With FTM And Experimental Study Of Drop Impact On Liquid Film

The process of droplet impinging on liquid film is ubiquitous in nature and industrial production,its strong heat exchange ability makes it widely used in chemical industry,energy industry and so on.It is very important for the design and working process of the related industrial equipment to carry on systematic and in-depth study to this process,the process of droplet impinging on liquid film is a typical motion problem of free interface,because of the momentum exchange after the impact,the topological changes of the interface are very complicated,in order to study the change of the interface of liquid droplet impinging on liquid film,in this paper,the numerical simulation is carried out by using the method of FTM(Front Tracking Method),the experimental observation platform is built by using the existing equipment of the research group to observe the droplet impinging on the liquid film.FTM was used to study the process of droplet impinging on liquid film and the phenomenon of entrainment,the corresponding mathematical physical model is established,through the analysis of mesh independence and the simulation results are compared with the experimental results obtained by previous scholars,the applicability and accuracy of the FTM method for droplet impinging on the liquid film is verified.After that,the influence of dimensionless parameters,such as We number,dimensionless liquid film thickness and Bo number,on the impact process and results is analyzed.The results show:(1)The pressure distribution at the initial stage of droplet impinging on the liquid film is:in the impact area,the pressure reaches the maximum at the wall and decreases with increasing height,in areas where the impact is not affected,the pressure does not change,after the droplet impact,the two contacts in the neck area to produce a small jet at first,this jet is the basis for the formation of late spray,after the formation of the spray,it will move to both sides,the width of the spray gradually increased,the height of the spray is first increased and then decreased;the thickness of the liquid film decreases with time.(2)At the initial stage of droplet impinging on the liquid film,the pressure field is related to the We number,with the increase of We number,the pressure at the wall is larger,We number is also related to the formation of water spray,when the We number is small,the droplet does not produce a jet at the initial stage of the impinging liquid film,and no water spray is formed after the collision,in addition,the increase in the number of We will increase the height of the spray,the decrease of the viscosity ratio of two phases will lead to the later formation time of water spray,which inhibits the formation of water droplets,the jet intensity decreases with the increase of the dimensionless liquid film thickness,the thickness of the liquid film also affects the shape of the spray,the greater the thickness of the liquid film is,the smaller the inclination angle between the water spray and horizontal direction is,but the greater the thickness of water spray.(3)The phenomenon of entrainment is caused by the formation of a crescent gas film in the process of falling liquid droplets to the liquid film,the liquid drop and the liquid film deform to form a concave,during the process of falling drops,when the gas in the middle part of the gas film has not escaped from the two ends and the liquid droplet and the liquid film are integrated,the phenomenon of entrainment is produced,after the gas film is produced,it is gathered under the action of surface tension and fluid shear force,and the air bubble is formed from the middle fracture,the thickness of the liquid film has little effect on the entrainment phenomenon,but it has a certain influence on the time of the formation of the film and the bubble,the bubble motion intensity is smaller,the Bo number has little influence on the formation of the film,but has a great influence on the formation of the bubble.The experimental observation platform is built by using the existing equipment of the research group to observe the droplet impinging on the liquid film,the influence of different impact parameters on the interfacial morphology was studied by two variables,the impact height and the liquid film thickness,the main conclusions are as follows: the main influencing factor of coronal spray is the impact height.In this experiment,when the impact height of 40 mm does not produce water spray,and when the impact height of 135 mm and 230 mm,both have a coronal spray,in the case of coronal spray,the rising time and the maximum height of the spray will increase with the increase of the impact height,the thickness of the liquid film does not affect the formation of coronal spray,but it has an effect on the time of the formation and collapse,with the increase of thickness,the time of spray formation and collapse is pushed back.