Study On The Preparation Of Micro Nano Structure On Copper Surface And Its Heat Transfer Performance

Since modern times,the rapid development of industry and high technology has accelerated the consumption of energy.Therefore,more and more people pay attention to the utilization and efficiency of energy.With the continuous development of high-tech,the requirements of heat engine,nuclear reactor,metallurgy industry air and other fields for the system heat dissipation capacity are constantly improved.Boiling heat transfer,as an efficient phase change heat transfer method,can obtain higher heat flow density and larger heat transfer coefficient under lower superheat.The principle of boiling heat transfer is applied to many heat dissipation systems,such as high-power microelectronic equipment,heat exchanger,large nuclear reactor,etc.At present,the methods of enhanced boiling heat transfer mainly focus on the change of the surface structure of the material,through the change of the physical and chemical properties of the material surface,so as to enhance heat transfer.In this paper,micro nanostructures and micro nanostructures were prepared on the surface of pure copper by laser processing.The hydrophobicity of different surface structures was obtained by contact angle measuring instrument,including droplet soaking time,contact angle,bubble contact angle and rolling angle.Based on the self-designed boiling heat transfer test platform,the boiling heat transfer performance of different structures was measured,and the movement of bubbles was recorded with a CCD camera.Including the analysis of SEM and EDS,the influence of laser processing oxide layer on the heat transfer performance was summarized by comparing the heat transfer experimental data.The main research work of this paper is as follows:(1)The removal mechanism of femtosecond and nanosecond laser processing pure copper substrate was studied in the experiment,and the influence of different laser processing parameters on the microstructure morphology was explored,such as scanning interval,scaning speed,energy density.By controlling the processing parameters,the morphology of microstructure can be accurately controlled.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and confocal observation were used to analyze the morphology,including size and composition of nanostructures.(2)The porosity,wettability and porosity of the prepared microstructures were measured.The contact angle meter is used to measure the static contact angle and immersion time of each sample.The static contact angle and rolling angle of the underwater bubble are measured when the sample is immersed in the water.Through porosity,wettability and air permeability,the rewetting ability of each structure can be determined.(3)The experimental platform of boiling heat transfer was designed and built independently.The platform was calibrated and modified to make the experiment data accurate and reliable.The samples were heated by voltage power supply and electric heating rod.The thermal data of micro-nano structure boiling experiment were obtained by K-type thermocouple and temperature data acquisition instrument.The bubble growth and movement in the whole boiling process were recorded by CCD camera,and the critical heat flux and heat transfer coefficient were calculated.The thickness of oxide layer formed by the process of nanosecond laser processing is large,which hinders the heat transfer.Compared with the smooth surface,the CHF decreases by 48% and the HTC decreases by 27%.For the change of superheat,when the nanoporous structure reaches CHF,the superheat is 7.9K earlier than the smooth surface.Femtosecond laser processing is cold processing with less oxide layer,Compared with smooth surface,CHF decreased by 16% and HTC increased by 58%.In addition,it can be noted that for the change of superheat,compared with the columnar structure before and after pickling,it is found that after pickling,the superheat of CHF is 4.5K ahead of time,the 12.5K ahead of time compared with smooth surface.