Freezing Behavior Of Impacting Droplet On Cold Surfaces

The freezing process of impacting droplets on cold surface has been investigated using both experimental and numerical methods.The main results and innovation are as follows:(1)The freezing process of impacting droplets on smooth and hydrophilic surface has been analyzed experimentally using a high-speed camera.The effect of the impacting speed,surface temperature and thermal conductivity of materials on the droplet spreading diameter,oscillation and freezing behavior were also investigated.A function to predict the freezing time was derived from thermodynamics condition.The calculated values were in good agreement with the experimental data,with the maximum relative error of less than 4.7%.(2)The freezing process of impacting droplets on hydrophilic grooved surface has been analyzed.Using LIGA method preparation of the micron-scaled grooved copper and decimillimeter-scaled grooved silicon plate.The effect of the groove dimension on the droplet spreading diameter of the parallel and vertical groove,and freezing time were investigated.Improved the theoretical prediction formula of water droplets freezing time,with the maximum relative error of about 10.8%.(3)The preparation of hydrophobic surface using acid etching and Ultra-Ever Dry method.Experiment of droplets impacting on different hydrophobic surface,four behaviors were observed: finger,rebounding,ejecting and breakup during rebounding.Proved that the hydrophobic surface freezes could delay the freezing of droplets.The rebounding and breakup dynamics,diameter’s spreading regularity were also analyzed.Meanwhile,preparing the hydrophobic/hydrophilic hybrid surface,foundingthe "guidance" and "cutting" and "convergence" phenomenon during the process of water droplets freezing,which has reference significance for anti-icing.(4)Large-scale Molecular Dynamics simulations are applied to study the dynamic processes of a nano-droplet freezing at the microscopic level.The effect of the surface temperature,potential energy ratio and microstructureon the droplet freezing behavior were also investigated,and the temperature gradient phenomenaare recorded and analysed.Verified the MD numerical simulation method was reasonable and effective.