Stainless Steel Surface Condensation Heat Transfer Enhancement By Nanosecond Laser Selective Micro-Texture

As an important energy transfer method,condensation heat transfer is widely used in many industrial fields like energy,chemical industry and electronics.With the continuous improvement of industrial level,efficient condensation heat transfer performance has gradually become a focus of attention.The chemical modification commonly used for special wettability surfaces has the disadvantages of high pollution,large thermal resistance,and long preparation cycles,and it is difficult to improve the condensation heat transfer performance of the existing superhydrophobic stainless steel surface.The texture technology and constant temperature heat treatment process were used to obtain a superhydrophobic-superhydrophilic wedge-shaped selection pattern on the surface of SUS304 stainless steel,and research the enhancement the condensation heat transfer performance.First,the surface morphology,three-dimensional profile and chemical composition of the laser selective micro-textured stainless steel surface were analyzed by scanning electron microscope,three-dimensional optical microscope and X-ray photoelectron spectroscopy respectively.In this paper,we use nanosecond pulsed fiber laser to orthogonally micro-texture the stainless steel surface,and then perform constant temperature heat treatment on the laser micro-texture stainless steel,We continue to use nanosecond laser to micro-textured part of the surface.Finally,obtained the selective micro-texture surface.The analysis of the instrument found that the micro-nano secondary texture was prepared by laser selective micro-texture on the surface.The degree of surface oxidation of the superhydrophobic region was greater than that of the superhydrophilic region.And SEM showed that the micro-nano fluff burr on the groove-convex surface was more abundant than the superhydrophilic area.Condensation heat transfer experiment test analysis shows that among original,superhydrophilic and superhydrophobic surfaces of stainless steel,the superhydrophobic surface has the highest condensation heat transfer coefficient(CHTC).While the CHTC of laser selective(4:1)micro-textured stainless steel surface can reach159.7±1.8W/(m~2·K),which is about 2.0 times of superhydrophobic surface.The average drop diameter of the condensation droplets is as low as 1.2mm,and it drops55%of the superhydrophobic surface.The superhydrophilic wedge-shaped channel on the micro-textured surface of the laser selective area has a self-driving effect on the liquid flow,so that the dropwise condensation area can be separated from the condensing surface in time,and the condensate on the stainless steel surface can be quickly gathered and dropped off,which significantly shortens the time of droplet stay on dropwise condensation area.The cycle of nucleation-growth-merger-shedding of condensed droplets in a new round and repeated,the average falling diameter of condensed droplets on the surface of the selected stainless steel is significantly smaller than that of the fully superhydrophobic surface.The residence time of the condenseddroplets are reduced in the dropwise condensation zone,which has a higher CHTC.