Study On The Characteristics Of Condensation And Frost On The Surface Of Bamboo Leaves And Its Biomimetic Preparation

Condensation and frosting are gas-liquid / gas-solid phase transitions that occur at the gas / solid interface,which often result in reduced engineering equipment efficiency and increased energy consumption.Therefore,it is of great significance to prevent or delay the occurrence of dew and frost.The front and reverse of bamboo leaves show different dew / frost behavior under the same environmental conditions.In order to investigate the reasons,this paper observes the micro-morphology,wettability and dew and frost behavior of bamboo leaves.The results show that the difference in waxy layer,nano-needle structure and surface wettability are the reasons for the different condensation and frost performance on both sides of bamboo leaves.For the reverse side of the bamboo leaves,a high contact angle increases the thermodynamic barrier when the vapor phase becomes nucleus;the wax layer and smaller contact area reduce droplet blocking work,the nano-needle structures provide greater Laplace pressure to drive droplets upward,so the surface energy released when droplets are combined drives the droplets to bounce,which delays the condensation process.The actual contact area of droplets on the surface of bamboo leaves will affect the droplet freezing and frost crystal growth during frosting.Compared with the front side of bamboo leaves,the reverse side of bamboo leaves with smaller contact area has better anti-frosting performance.In order to further explore the relationship between the condensation and frost characteristics of bamboo leaf surface and its microstructure,low surface energy and wettability,the bionic structures were designed based on the micro-morphology of bamboo leaf surface.Bionic structure I was constructed by wire-cut electrical discharge machine and bionic structure II was constructed by laser processing and sol-gel-hydrothermal method.The wettability was used as the evaluation standard to optimize the processing parameters and realize the preparation of bionic structure surface.The condensation and frost performance of the bionic surface were tested using the condensation and frosting test bench.The results show that increasing the hydrophobic properties of the material surface can increase the thermodynamic barrier during water vapor nucleation,thereby delaying water vapor nucleation;the low surface energy and nano-needle structure reduced the blocking work of the droplets,so the surface energy released when the droplets merge can drive the droplets to bounce off the sample surface.During the frosting process,the actual contact area of the micro-droplets on the sample surface will affect the freezing rate of the micro-droplets.The smaller the contact area,the slower the freezing rate.the contact state of the frozen droplets will affect the heat transfer process of water vapor,thereby affecting the growth of frost crystals.