A Numerical Simulation Of Droplet Impacting On A Hot Wall

As a representative of heat dissipation with phase change,spray cooling technology sprays atomized droplets onto the surface of electronic components and takes away heat by evaporation.The equivalent heat transfer coefficient of spray cooling is much higher than heat dissipation methods by using gas or liquid convection.It makes spray cooling a better choice for the cooling of marine electronic equipments.Droplets impacting on a hot wall is an important procedure of spray cooling.In this paper,gas-liquid interface of droplet was tracked by diffuse-interface method which was implemented in the open source library for computational continuum mechanics Open FOAM~@.And the boundary conditions of equilibrium contact angle and dynamic contact angle for the diffusion interface method were successfully applied.According to Dalton’s law of partial pressure,the mass fraction of saturated vapour on the interface was obtained,and the evaporation rate is further obtained.The governing equations,which were solved in Open FOAM~@,were modified in accordance with the heat and mass transfer across two-phase interface.The accuracy of the numerical method was verified in the three cases(the steady-state distribution of phase field variables,the spreading of droplets on a flat plate and the evaporation rate of droplets on a flat plate)related to spray droplet impacting on hot wall.The influence of Marangoni effect on the process of spray droplets hitting the hot wall was analyzed.It was found that the Marangoni flow caused by the temperature gradient would inhibit the spread of the droplets on the wall and promote retraction of the spray droplets on the wall.Eventually Marangoni flow causes the internal flow of the droplet after reaching a quasi-steady state.Considering the droplets with different surface tension temperature coefficients,the influece of Marangoni effect on the dynamic process of spray droplets hitting the hot wall was further studied.A linear relationship between the temperature coefficient of surface tension and the maximum wetting radius of the droplet and the minimum droplet height was found.In other words,there is a linear relationship between the a priori Marangoni number and the maximum spread of the droplet.