Research On Heat And Mass Transfer Performance Of Bionic Hydrophilic-hydrophobic Functional Surface Based On Desert Beetle Elytra Structur

Phase transition in Gas-liquid condensation is a fairly common phenomenon in industrial production and daily life,such as water harvesting in arid regions,heat exchangers for heavy industry and microelectronic components,and energy production in the nuclear industry.Improving the efficiency of condensation is important for promoting environmental protection and improving the efficiency of industrial production.In order to improve the condensation efficiency of liquid droplets and to optimize the performance of liquid-filled devices such as heat sinks and vapor chamber,we can refer to the answers given by plants and animals in nature.It has been shown that the elytra of the Namib desert beetle has excellent fluid collection properties.this paper based on the elytra structure of Namib desert beetles,different wettability surfaces were prepared and their heat and mass transfer properties were investigated by chemical etching and hydrophobic coating spraying.The main research contents and results are as follows:Using flat and hemispherical 6063t5 aluminum alloy as base and the specimen was chemically etched in alkaline ammonium persulfate solution to form a hydrophilic surface,cured by UV photosensitive adhesive and UV photosensitive adhesive to form a temporary protective cover layer in the protruding area,sprayed on the surface of the specimen with nano-silica coating as a hydrophobic coating,and peeled off the UV photosensitive adhesive to obtain a biomimetic hydrophilic-hydrophobic composite wettable surface.A visualized experimental platform was built to perform condensation and heat transfer experiments on specimens with different wettability and surface characteristics.The effect of different chemical etching time and Si O₂:Ethanol coating mass ratio on the surface wettability of 6063t5 aluminum alloy was investigated.As the chemical etching time of6063t5 aluminum alloy specimens in alkaline ammonium persulfate solution increased,the surface contact angle showed a decreasing trend,and the contact angle reached the minimum（about 4.2±1.2°）at the etching time of 30 min,and the surface shows superhydrophilic-state at this time.The contact angle reaches the maximum（about 151.3±1.5°）when the coating mass ratio is 2:1,and the rolling angle、hysteresis angle is less than 5°,which shows superhydrophobic-state.The Si O₂ coating modified on the chemically etched aluminum alloy surface will have a better hydrophobic-wettability effect,which will improve the hydrophobic coating by about 15.33%compared with the non-chemical etched one.The surface wetting state and droplet transport behavior of each specimen under the fog flow were analyzed in the condensation experiments,and the condensation collection capacity of each specimen was compared at the fog flow rates of 1,1.5 and 2 m/s,respectively.The experimental results showed that the condensation state of the hydrophilic surface was liquid film-like condensation,while the hydrophobic surface was liquid droplet-like condensation,and the collection efficiency of the pro-hydrophobic composite surface was better than that of the common 6063t5 aluminum alloy surface,pure hydrophilic surface and pure hydrophobic surface,respectively.The condensation collection rate of the bionic hydrophilic-hydrophobic composite surface reached 1404.32mg/cm²·h at a mist flow rate of v_f=1m/s,which is 2.75 times,1.22 times and 2.36 times higher than that of the superhydrophilic surface,superhydrophobic surface and ordinary 6063t5 aluminum alloy surface,respectively.It has good condensation and liquid collection ability.The heat transfer coefficients of the composite surfaces with protrusion diameters of 2、4、6 mm were 18.23k W/m²·k,27.52k W/m²·k and 22.68k W/m²·k,respectively,which were 278.74%,420.79%and 346.78%higher than the common surfaces when the subcooling degree is 10K(h _OAS=6.54k W/m²·K).It is demonstrated that the biomimetic hydrophilic-hydrophobic composite surface based on the beetle elytra structure has good heat transfer performance.