A Study On Fluid And Thermal Dynamics Of Droplet Impact On Heated Hydrophobic Surface

The impact of droplets on high-temperature hydrophobic surfaces is a research on droplet impact that has emerged in recent years,and its results can be widely used in energy and power,aerospace,engineering applications and other fields.Since the droplet impact process involves theories of gas-liquid two-phase flow and heat transfer,the study of this process can not only improve the related theories,but also has important guiding significance for improving the corresponding engineering design experience.In this paper,deionized water is used as the research object,and the flow and heat transfer characteristics of droplets hitting a horizontal hydrophobic surface under different initial conditions are studied by simulation methods.In this paper,firstly,a two-dimensional numerical model of droplet impact is constructed by the compressible Inter Foam solver in the open source simulation software Open FOAM,and compared with the experimental results to verify the accuracy of the model.A dynamic contact angle model is added to the model to solve the hysteresis effect of contact angle.At the same time,this paper uses the VOF method to capture the gas-liquid interface of the droplet,and the CSF method is used to calculate the surface tension on the gas-liquid interface,which eliminates the discontinuous jump on the free interface of the fluid.Subsequently,the impact speed(0.107m/s-1.77m/s)and droplet diameter(0.07mm-11.5mm)on the impact of droplet flow characteristics were studied,and the changes in the flow process of droplets impacting on hydrophobic surfaces were explored,revealing the maximum spreading coefficient,The contact time changes with the We number,and its theoretical mechanism is analyzed.The results show that:at different impact speeds,the maximum droplet spread coefficient?and(2(20)0)^0.25(We>10)are linear;and at different initial diameters,the maximum droplet spread coefficient?and(2(20)0)^0.35(We>10)A linear relationship.The droplet contact time varies little under different impact speeds,and under different initial diameters,the contact time has a linear relationship with(2(20)0)^1.5Finally,the impact of droplets on high-temperature hydrophobic surfaces is simulated,and the effects of impact velocity,droplet diameter and initial droplet temperature on droplet heat transfer characteristics are studied,with emphasis on the analysis of droplet temperature,heat flux and cooling effectiveness changes.The results show that the heat flux is less affected by the initial droplet velocity,but increases with the decrease of the initial diameter and initial temperature of the droplet;the cooling effectiveness increases with the increase of the impact velocity and initial droplet temperature.With different initial diameters,the cooling effectiveness of droplets generally shows an increasing trend.Based on the numerical simulation method,this paper conducts a comprehensive study on the flow and heat transfer characteristics of the droplet hitting a high-temperature hydrophobic surface,and also conducts a more comprehensive discussion on the influence of different parameters.The research results of this paper provide some ideas and simulation experience for the research of micro-droplet impact on high-temperature hydrophobic surfaces,and also provide theoretical foundation and support for engineering applications such as inkjet printing and spray cooling.