The Freezing Process Of Water Droplets On The Surface Of Insulator With Superhydrophobic Coating And Its Influencing Factors

Because of its special ability of low adhesion strength, delayed ice crystallizationand bouncing, which might deice and delay the ice on transmission lines and insulators,the superhydrophobic coating become the focus of current research. While, there are tillsome controversy on whether the superhydrophobic surface have the actual anti-icingcapabilities. Especially on the basic problem of icing characteristics ofsuperhydrophobic surface about the influence of water droplets motion characteristicsand water droplets freezing process,there aren’t, in-depth research. In order to revealthe microscopic freezing process of water droplets on the surface of coating, andprovide a reference for the study of application of anti-icing superhydrophobic coatingon insulator, this study finished the rolling test, icing test of water droplets and icing testof insulators covered with superhydrophobic or hydrophobic surface coatings in theartificial climate chamber.The main achievement shown as follow:The dynamitic motive process of water droplets on the superhydrophobic orhydrophobic surface with continuous spraying supercooled water was gained in the lowtemperature and low pressure chamber, and the motion characteristic of the waterdroplets was studied, too. And the influences of static contact angle, contact anglehysteresis, roughness, and environment temperature to the motion characteristic wereanalyzed. Results indicate that, on the samples’ surfaces, the water droplets will not rolloff from the surface until it’s diameter increased to a certain size D。 And the larger thecontact angle is, the smaller the contact angle hysteresis is, the larger the roughness is,the larger the tilt angle of the surface is, the smaller the average diameter D of thedroplets is, the smaller volume of water droplets that can accumulate on the surface is,the shorter residence time is, the less possibility freezing of the droplets is.Through the utilization of the microscope, the dynamic processes of thecrystallization and nucleation for the static water droplets on the superhydrophobic orhydropbic surface and water droplets under the condition of continuous spray withsupercooled water droplets were both gained, the freezing nucleation mechanism and itsinfluence factors were analyzed, and the time for the appearance of the frozen waterdroplets under two different situations were counted, too. The contrast experiments forthe hydrophobic surfaces with the different contact angle or contact angle hysteresiswere carried out, and the influences of the contact angle, contact angle hysteresis and other factors to the freezing time were studied, too. Since static water droplets do notreflect the motion characteristics of water droplets on superhydrophobic or hydrophobicsurfaces, its freezing time is also not suitable enough to reflect the delay time of theicing formation for the different surfaces under the continuous spray situation. Wesuggest using the test method with continuous spray when studing the application ofsuperhydrophobic coating, and using the time of the durations of locally frozen droplets’collapse, absolutely frozen droplets, or time of the surface entirely covered by ice layerson the sample are proposed in this paper to evaluate the super-hydrophobic surface’sability of postponing icing.Experiments of icing growth of insulators with different coatings were carried outin the artificial climate chamber. And the effects of the superhydrophobic orhydrophobic coating on the icing growth were studied. The result shows that,superhydrophobic or hydrophobic coating can delay icing on the insulator in a certainextent, the larger the contact angle is, the smaller contact angle hysteresis is, the betterthe droplets rolling characteristics and longer icing delaying time will be. And,superhydrophobic or hydrophobic coating affects the morphology of the ice of thesurface rather the ice density and morphology of icicles.the coatings affects the weightof icing on the insulator surface and the growth of insulator surface icicles only in theearly icing period.