Preparation Of Super-hydrophobic Surface Of Silicon Substrate And Research On Its Heat Transfer Performanc

Steam condensation is widely present in industrial production and daily life due to the large amount of latent heat released during the gas-liquid phase transition process of steam.According to the condensation morphology of droplets on the condensation surface,the condensation forms can be classified as dropwise condensation and filmwise condensation.The current research showed that the condensation heat transfer coefficient of dropwise condensation is much higher than that of filmwise condensation.Therefore,it is of great significance to promote the formation of dropwise condensation on the condensing surface to enhance condensation heat transfer and save energy.Dropwise condensation usually occurs on hydrophobic/superhydrophobic surfaces,where micro-nano structures have poor mechanical stability.In this paper,a superhydrophobic surface is designed,the hydrophobic particles on the surface are protected by a micro-pyramid base structure.And the surface of this structure can achieve dropwise condensation in the process of condensation heat transfer,with good condensation heat transfer performance,and at the same time,the surface has good mechanical stability.The main research contents and results are as follows:（1）Micro-pyramid substrate and micro-column substrate were prepared by chemical etching,photolithography and dry etching on silicon wafer（100）,and the candle soot was used as the template of hydrophobic particles,which was deposited between microstructures to obtain micro-nano composite superhydrophobic surface.（2）The wettability and mechanical stability of the prepared superhydrophobic surface were investigated.The static contact angle of the microcolumn substrate is 156°,but the rolling angle is also as high as 40°,and the surface is superhydrophobic after the deposition of hydrophobic particles,and the rolling angle decreases to about 1°.After the deposition of hydrophobic particles on the substrate surface of the micro-pyramid with different etching time,the surface wettability changes from hydrophilic to superhydrophobic,the contact angle ranges from 152°to 154°,and the rolling angle of the droplets is about 1°,and the contact angle is stable above 134°after 30 times of wear,which indicates that the superhydrophobic surface of the pyramid microstructure substrate has good mechanical stability.（3）The dynamic behavior and heat transfer performance of condensation droplets on the sample surface were analyzed by a visual heat transfer platform.The results show that the surface with etching time of 30 min and 35 min shows the best mechanical stability and heat transfer performance,the condensation droplets on the surface had a minimum departure diameter（2.35 mm to 2.51 mm）and a maximum departure frequency(232±7min^-1).At low subcooling（～3K）,the droplet departure diameter（2.19 mm to 2.37 mm）was smaller than that before wear,which corresponded to a higher droplet departure frequency(52±4 to 79±3 min^-1).Moreover,the droplet circulation efficiency and heat transfer performance of the micro-pyramid substrate surface are superior to those of the micro-column substrate surfaces under the same undercooling,and the heat transfer performance of the micro-pyramid substrate with etching time of 30 min and 35 min is superior to other etching time surfaces.When the subcooling is about 10K,the heat flux and heat transfer coefficient of the surface etched for 30 min and 35 min are 190.2 k W/m²,190.0 k W/m² and21.33 k W/m²K,21.30 k W/m²K respectively,which are about 72%stronger than that of the hydrophilic surface.After wear,the surface of the micro-pyramid still has good heat transfer performance,and the surface heat flux is 86.47%～103.63%higher than that of the ordinary hydrophilic surface at high supercooling（～17K）.