Effects Of Hydrophobic/Hydrophilic Surfaces On Characteristics Of Wetting And Freezing Of Water,and Frosting Under Natural Convection Conditions

The present study experimentally investigates the effects of hydrophobic/hydrophilic surface structures on the characteristics of wetting and freezing of a single water droplet,and the frost accumulation under natural convection conditions.Semiconductor cooler and contact angel measurement systems are fabricated to conduct the experiment.By high-speed photography,contact angle measurement and other equipments,the wetting,freezing and frosting processes on different morphologies hydrophobic/hydrophilic surfaces are acquired.The wettability of water on different morphologies surfaces is studied firstly.The effects of chemical etching time,micro-and nanostructure(including the shape,size and arrangement mode),droplet volume,surface temperature,environmental humidity and other factors on the wetting of hydrophobic/hydrophobic surfaces are investigated.Comparing the hydrophobic property of different surface topographies,the most proper surface structure and clinder morphology with high contact angle is obtained.The influences of droplet volume,surface topography and testing conditions(including temperature and humidty)on the surface hydrophobicity arequantitatively analyzed.Secondly,single water droplet freezing processes on different morphologies hydrophobic/hydrophilic surfaces under constant or varying surface temperatures are studied.Droplet thickness and diameter are measured.The influences of surface temperature,environmental humidity and surface topography are investigated.Besides,the differences between the first and second freezing periods of water droplet are compared.The deformation characteristicsare quantitatively analyzed.It is found that surfaces produced with micro-pillar silicon,black silicon and two-stage black silicon can largely reduce the freezing thickness deformation and delay the freezing time.In addition,temperature and humidity have significant effects on freezing process.Two-stage black silicon is found to have the best durability.Finally,the frost accumulation processes on hydrophobic/hydrophilic surfaces under natural convection conditions are investigated.Visualization results of frost layer growth with time and temperature are obtained via a CCD carema.It has been verified that periodic structures play an important role in respect of anti-frosting.Besides,it is shown that there is no obvious correlation between contact angle and frost layer thickness.In addition,the frost layer structure of micro-pillar silicon shows the best anti-frosting performance.