Condensation And Water Catchment Characteristics Of Nanograssed Micro-V-Groove Copper Surfaces

Surface wettability plays an important role in phase change heat transfer.Dropwise condensation superhydrophobic surfaces are widely used in thermal management and water harvesting technology.In recent years,Researchers have fabricated many micro-nano hierarchical superhydrophobic surfaces and investigated the effects of surface microstructures on droplet state and heat transfer.The static contact angle of external droplets on the surface is an important criterion to evaluate the wettability of the surface.The dynamic behavior of condensate droplets such as migration and merging on superhydrophobic surfaces has an important influence on the surface heat transfer characteristics.Based on the existing theoretical models,the heat transfer characteristics of superhydrophobic surfaces are studied,and the influence of surface microstructure on heat transfer effect is described.The main research contents and achievements are as follows:The nanograssed micro-v-groove copper surfaces,nanograssed micropyramidal copper surface and nanograssed micro-semi-pyramidal copper surface were fabricated by mechanical processing and chemical etching.As a contrast,nanostructured hydrophobic copper surfaces,smooth hydrophobic copper surfaces and smooth hydrophilic copper surfaces were fabricated.The dynamic model of contact angle during the growth of condensate droplets and the static contact angle model of external droplets on different microstructures were established.The static contact angle and rolling angle of external droplets on superhydrophobic surfaces were measured.The results show that the contact angle of external static droplets is larger than 150 degrees and the rolling angle is about 0.9 degrees,which indicates that the fabricated samples exhibit really good superhydrophobicity.The heat transfer model of small single condensate droplet and the size distribution model of the droplets on the surface are established.The influence of the nanostructures on small condensate droplets spontaneous migration frequencies and the influence of the surface inclination angle on the size distribution of the condensate droplets are investigated.The dynamic behavior and the size distribution of droplets on nanograssed surfaces with different inclination angles were observed by an optical microscope.The dynamic behavior of dropltes on hydrophilic surface were also observed.The results show that nanostructures can accelerate the spontaneous migration frequency of condensate droplets,and the size of residue droplet on the surface become larger with the decreasing of the surface inclination angles.Establish the heat transfer model and growth model of single reservoir droplet,and consider the influence of microstructures on the weight of collected condensate water.The dynamic behavior of the reservoir droplets was observed by an optical microscope,and the weight of the collected condensate water was measured by an electronic balance at intervals.The results show that the dynamic behavior of reservoir droplets coincides with the model,and the nanograssed micro-v-groove surface collected more water than any other surfaces,which indicates that the micro-v-groove surface has the highest heat exchange efficiency.In this paper,the factors affecting the condensation efficiency of micro-nano hierarchical superhydrophobic copper surface are investigated by experimental methods.The effects of micro/nano structures on the contact angle of droplets,the spontaneous migration of condensate droplets and the weight of collected condensate water are studied,which can be referenced in the design and optimization of micro/nano structures on heat transfer surfaces.