| The physical phenomenon of droplet impingement on a high temperature hydrophobic surface exists in a variety of fields,such as spray cooling of electronic components,fuel injection combustion in engines,and thermal spray coating.Rebound is the most significant motion state of droplets on hydrophobic surfaces,and when droplets are simultaneously subjected to high-temperature walls,the presence of a bottom vapor layer affects the kinetic and thermodynamic behavior of droplets on hydrophobic surfaces,which is different from that of droplets on ambient surfaces.Therefore,an in-depth study of the motion and heat transfer behavior of droplets on high-temperature hydrophobic walls can not only reveal the influence law of different factors on the dynamic characteristics of droplets on high-temperature hydrophobic surfaces and find an effective method to manipulate the bounce behavior,but also provide theoretical guidance for the innovative development of related engineering applications.In this paper,the droplet bounce behavior of droplets on different temperature homogeneous hydrophobic surfaces is experimentally studied with high temperature hydrophobic walls as the research object,and the manipulation suppression effect on droplet bounce behavior and the influence on the overall heat transfer capacity is further investigated by numerical simulation methods of droplet impacting different twodimensional non-homogeneous hydrophobic surfaces and three-dimensional nonhomogeneous pattern surfaces.The main research contents and conclusions are as follows.(1)A visualization experimental setup for droplet impact on a high-temperature wall was built to observe the motion state of droplets on a high-temperature homogeneous hydrophobic surface,especially the bounce behavior.We-T phase diagrams were produced using different forms of droplet bounce processes after droplet impact at different initial Weber numbers and wall temperatures,and it was found that the droplet motion bounce state was mainly affected by the initial Weber number and less by the wall temperature;the analysis results showed that the vapor layer formed on the hightemperature wall surface could maintain the integrity of the droplet to a certain extent and improve the initial kinetic energy of the bounce,and the maximum bounce height also increased with the temperature rises.(2)A two-dimensional non-homogeneous hydrophobic wall simulation model is established to discuss the biased bounce motion process of droplets hitting different nonhomogeneous hydrophobic surfaces,and the increase of wettability difference will intensify the biased bounce of droplets and reduce the maximum bounce height;considering the heat transfer process of secondary impact,it is found that the heat transfer of primary bounce is always higher than that of secondary bounce,and due to the reason that the biased jump produces secondary tilted impact,the non-homogeneous wall can increase the average heat flow density of the wall and improve the heat transfer effect on the basis of maintaining the hydrophobic performance.(3)A three-dimensional non-homogeneous patterned surface simulation model was established to explore the spreading,shrinking and bouncing processes of droplets under different pattern wettability differences,droplet initial velocities,and the positions and sizes of patterns.The results show that the distribution of velocity field inside the droplet indicates that the droplet is influenced by the difference of pattern wettability during the motion process;the spreading area ratio of the droplet at different moments is influenced by the initial velocity of the droplet,and the position and size of the pattern will affect the spreading area ratio at different moments to some extent;the change of these factors will cause the opposite trend of droplet residence time and maximum bounce height,and the most important reason is the high viscous force on the pattern high viscous force,which is promoted during spreading and inhibited during shrinkage. |
PDF Full Text Request