Study On Surface Heat Exchange Characteristics Of Micro/Nano Structures Fabricated By Femtosecond Laser

Due to the rapid development of technology,the ultra-large-scale integrated circuits have made the high power density characteristics of electronic devices more and more obvious.The large amount of heat generated on the surface of high heat flux density components directly affects the stability and service life of electronic equipment.The same problems also appear in the nuclear power industry,military industry,agriculture and other fields.At present,the cooling effect that conventional cooling systems has been greatly challenged,and boiling heat transfer is one of the most effective ways to solve this problem.The two most important parameters in the boiling process are the critical heat flux(CHF)and the heat transfer coefficient(HTC).CHF determines the maximum heat dissipation power and safety limit of the system,and HTC determines the heat transfer efficiency of the system.Therefore,CHF and HTC need to be improved in practical application to ensure the efficient and safe operation of the equipment.Current research shows that micro/nano structures have a significant effect on enhancing surface heat transfer performance.Based on the femtosecond laser micro/nano structure surface preparation technology,an experimental study on enhancing boiling heat transfer performance of solid surface micro/nano structure was carried out.According to the application background,experiments were performed on silicon wafers and nickel and zirconium metals as samples.An experimental measurement platform for visual boiling heat transfer performance parameters(CHF and HTC)was designed and built.The specific research contents are as follows:In terms of semiconductor silicon wafers,four typical micro/nano structures,such as pillars,corrugations,holes,and grooves,were prepared on the surface of the silicon wafer using femtosecond lasers for the study of boiling heat transfer performance.Scanning electron microscope(SEM)and contact angle measuring instrument were used to characterize the micro-morphology and solid-liquid static contact angle of the surface,respectively.The experimental results of pool boiling heat transfer under normal pressure show that the CHF and HTC on the surface of the micro-nano structure are significantly higher than those on the smooth surface,showing good heat transfer characteristics.The improvement of the boiling heat transfer performance of the channel structure is considerable,and the simultaneous improvement of CHF and HTC is realized.The maximum CHF reaches 1.5×10~6W/m~2,which is a 96%increase compared to a smooth surface;the maximum HTC reaches 4.9×10~4W/m~2·K,a 256%improvement over a smooth surface.After analysis,we believe that the channel structure has a strong capillary effect and good wetting,so that the boiling working fluid can quickly flow in the channel,the supply liquid can reach the evaporation surface in time to form a micro-liquid layer and generate bubbles.This will not cause a lot of local overheating area and avoid burning the surface.The flow of boiling working fluid in the channel increases the heat exchange coefficient and greatly improves the heat exchange performance.This heat exchange mechanism helps to delay the arrival of CHF.These experimental results and mechanism analysis are of great significance to the field of electronic device heat dissipation.For metallic surfaces,we used femtosecond lasers with different pulse energies to produce periodic corrugated structures on nickel surfaces.The results of boiling experiments show that the surface heat transfer performance is affected by the structure size.Among them,the surface CHF and HTC prepared with an energy of 0.02m J were simultaneously increased.CHF reached 2.2×10~6W/m~2,which was 108%higher than that of a smooth surface,and HTC reached 3.06×10~5W/m~2·K,which was a 574%improvement over a smooth surface.For metal zirconium,respectively in different laser energy was prepared by three sets of samples,from the analysis of experimental results,the metal zirconium 2 samples at 69?to CHF 2.8×10~6W/m~2,increased by 254%compared with the original surface,HTC up to 4.1×10 ~4W/m~2·K,173%of the original surface.It is found that the capillary effect on the surface of superhydrophilic structures is the main factor affecting boiling heat transfer.These research results have important application significance in the nuclear power industry and other fields.