Front Tracking Method Numerical Simulation Of Flow And Heat Transfer In Droplet Impact Onto Liquid Film

The process of a droplet impacting liquid film is widely used in natural phenomena,chemical production,nuclear power equipment,electronic components,etc.Recently,a series of researches have been focused on the evolution of fluid flow after droplet impact and the heat transfer between fluids and liquid-solid interface.The research on the flow and heat transfer characteristics of droplet impinging on liquid film is beneficial to enhance the heat transfer performance of high-power electronic devices and improve the production efficiency of industrial equipment.Therefore,the in-depth study of droplet impinging on liquid film has great engineering application value.The Front Tracking Method(FTM)reconstructs the moving interface by using the physical properties of the mathematical solution of the moving interface,which can accurately capture the gas-liquid interface without nonphysical phenomena.In this paper,the dynamic process of a droplet impacting liquid film under different parameters is simulated by using the interface tracking method.Firstly,the numerical results were compared with the analytical solutions and experiments to verify the correctness of the proposed model,and the evolution process of the interface between the droplet and the high-temperature wall covered with a static thin liquid film was studied.At the same time,the effects of initial impact velocity,dimensionless film thickness,and surface tension coefficient on heat transfer were analyzed.The results showed that according to the characteristics of heat flux distribution after impact,the liquid film surface area affected by the impact could be divided into three zones: the impact zone,the transition zone,and the static zone.Forced convection was the main heat transfer mechanism in the droplet impingement zone due to the droplet impingement.Increasing the initial impact velocity and decreasing the dimensionless thickness of the liquid film will enhance the heat transfer.With the initial impact velocity of the droplet increasing,the disturbance caused by the impact increases.Under the combined action of momentum and energy,the average heat flux increased significantly,and the coronal spray phenomenon in the impact zone became more obvious.With the thickness of the dimensionless liquid film decreasing,the average heat flux increased,and the heat transfer time kept longer.The surface tension coefficient had little effect on the heat transfer in the early stage of droplet impact.In the middle and late stages of impact,with the surface tension coefficient increasing,the average heat flux and temperature on the surface of the liquid film decreased at the same time,and the deformation degree and entrainment effect of coronal spray decreased.The initial height of droplet affected the change trend of heat flux in the initial stage of impact,but had little influence on the overall evolution of average heat flux on the surface of liquid film.In the process of spray cooling,the droplet may strike the solid or liquid surface with different inclined angles.In addition to the impact of the droplet,the liquid film produced a certain flow due to the influence of oblique gravity acceleration.The flow and heat transfer processes were more complex and difficult to predict.Therefore,it is of great practical significance to carry out numerical simulation of the process of droplet impinging on the inclined liquid film by using the interface tracking method,and to explore the influence of the inclination angle of the liquid film,the initial impact velocity of the droplet,the dimensionless thickness of the liquid film and the acceleration of gravity on the flow and heat transfer characteristics.The results showed that: more collision energy was transferred to the downstream liquid film during the droplet impact so that the downstream liquid jet propagated faster,and the heat flux value presented an obvious asymmetric distribution,the heat transfer enhancement effect in the downstream region was greater than that in the upstream region;The smaller inclination angle is more conducive to the overall heat transfer enhancement of the impact process,and a larger inclination angle led to the flat surface of the liquid film at the initial stage The results showed that the decrease of average heat flux lasted longer;the larger impact velocity was more conducive to enhance heat transfer,and the heat transfer enhancement effect was the most obvious in the early and middle stages of the impact process;the smaller dimensionless liquid film thickness was more conducive to heat transfer,and the higher level of average heat flux lasted longer.However,the thicker the liquid film was,the better the fluidity was,so the average temperature on the surface of the liquid film was smaller;With the gravitational acceleration increasing,the average heat flux on the surface of the liquid film increased at the same dimensionless moment,and the greater the gravitational acceleration was,the more obvious the enhancement effect of heat transfer was in the later stage of the droplet impact process.