| The phenomenon of droplet hitting the wall widely exists in material science,aerospace and other fields.At present,the research on the phenomenon of droplet hitting the wall mainly focuses on the droplet movement rule after a single droplet hitting different walls or liquid films.There are few studies on the phenomenon of continuous droplet hitting the wall,which is more complicated in motion law and heat transfer characteristics,but it is more common in industrial applications.Therefore,the study of droplet movement and heat transfer mechanism after continuous droplet impact on hot wall is of great significance in the field of droplet impact.In order to carry out the research work of this experiment,this paper independently designed and built the experimental platform for the motion characteristics and heat transfer characteristics of the droplet hitting the wall,and introduced the experimental system and experimental scheme.Four kinds of copper plates with different microstructure designed by ourselves were used as the base for the experimental study of droplet impact on the hot wall.The dynamic and heat transfer characteristics of deionized water droplet impact on the hot wall were studied on this experimental platform.The dynamic and heat transfer characteristics of deionized water droplets under membrane heat transfer were investigated at 60℃.The results show that the droplet impinges on the surface of four kinds of copper plates and then goes through the process of spreading,retracting and oscillating,and finally stabilizes on the surface of the copper plate.When the impact velocity is low,the surface of the droplet will be stepped after hitting the wall.There is no breaking and splashing phenomenon after the droplet hits the plate and the copper plate with the square column and hemispherical microstructure,but the breaking and splashing phenomenon occurs after the droplet hits the copper plate with the triangular prism microstructure.With the increase of the impact velocity,the ladder-like phenomenon on the surface of the droplet disappears,and there is no breaking and splashing phenomenon after the droplet hits the plate.The breaking and splashing phenomenon occurs after the droplet hits the copper plate with hemispherical microstructure,and the splashing phenomenon is more intense after the droplet hits the copper plate with square columnar and triangular prism microstructure.The analysis of heat flux on the surface of the copper plate shows that the heat flux after the impact of liquid droplets on the copper plate or liquid film can be divided into two stages according to the change of heat flux value: droplet collision stage and solid droplet evaporation stage.The heat flux value of the copper plate changes greatly in the droplet collision stage,while the heat flux value of the copper plate is relatively stable in the solid droplet evaporation stage.The dynamic and heat transfer characteristics of deionized water droplets under nuclear boiling heat transfer were investigated at 110℃.The results show that in the nuclear boiling heat transfer mode,the droplet on the surface of four kinds of copper plates goes through the process of spreading,shrinking and boiling vaporization successively.After the liquid droplets contact the copper plate,a violent boiling heat transfer phenomenon occurs,and a large number of bubbles are generated inside the droplet,which increases the spreading diameter of the droplet.Along with the rupture of the bubbles inside the droplet,the droplet occurs a violent splashing phenomenon.When the impact velocity is low,the droplet impact on the plate and the copper plate with square columnar and hemispherical microstructure does not have the spluttering phenomenon,but the droplet impact on the copper plate with triangular prismatic microstructure does have the spluttering phenomenon.With the increase of the impact velocity,there is no splash phenomenon after the droplet hits the plate,but the splash phenomenon occurs after the droplet hits the copper plate with hemispherical microstructure,and the splash phenomenon is more intense after the droplet hits the copper plate with square columnar and triangular prismatic microstructure.The analysis of heat flux on the surface of the copper plate shows that in the nuclear boiling heat transfer mode,the heat transfer after the impact of liquid droplets on the copper plate or liquid film can be divided into two stages: droplet collision stage and solid droplet boiling stage.The heat flux value of the copper plate changes greatly in the droplet collision stage,while the heat flux value of the copper plate is relatively stable in the solid droplet boiling stage. |
