The Morphology Characteristics Of Single Droplet Beam Impact On Liquid Film/Metal Surfaces

Spray cooling is an effective cooling technique with high heat release rate and good heat dissipation and uniformity,which has important contribution to heat and mass transfer.Therefore,it is widely used in the cooling of iron and steel industry,the impact of oil droplets on the oil film surface of the cylinder in the engine,the impact of lubricating oil droplets on the bearing wall in the aerospace field,and other fields.All of the above applications are cooled by impinging droplets on a metal/liquid film.However,it is difficult to study the phenomenon because of the small droplet size,incoherent impact and secondary droplet breakup.In order to improve the heat transfer,achieve the best cooling effect and avoid the surface crack,it is necessary to pay attention to the heat transfer of the interface.The research based on the visualization method of high-speed camera,an experimental platform was established for single droplet beam impinging on metal/liquid film,revealing the change law of the interface morphology of the metal/liquid film after the single droplet beam impinges on it,by quantifying dimensionless parameters,the influence degree of different influence factors on the shape change was determined,and the problems of complicated influence factors and strong randomicity in spray cooling were solved,better feedback on the spray cooling theory to reveal the above phenomenon,reveal the reasons for the morphology change,and provide a theoretical basis for the subsequent exploration of the state of the heat transfer interface,it is of positive significance to further master the heat transfer of high temperature interface.The experimental results show that the maximum spreading factor of the impact surface increases with the increase of the particle size and velocity of the single droplet beam,and the "pie" spreading edge perturbation has a "predictive effect" on the "liquid crown";With the increase of the wall roughness,the edge of the impact interface spreading process becomes more unstable and more prone to spatter,and the critical Weber number of splash will decrease.With the increase of the temperature of the liquid film,the splashing tendency is more likely to occur when the single droplet beam impinges on the interface of the liquid film,the second droplet is more likely to detach from the liquid film;When the viscosity of the liquid film increases,the single droplet beam impinges on the interface of the liquid film to produce "liquid crown" and the splashing tendency becomes less and less,and gradually evolves into the fusion first and then the formation of capillary wave diffuses to both sides,and gradually evolves into the fusion first and then the formation of capillary wave diffuses to both sides.Finally,the time variables in the single droplet“beam”of the study objects are highlighted.The dimensionless parameters of a single droplet beam impinging on a liquid film with different properties can be predicted when the Ohnesorge number of the liquid film is known.