Study On Laser Surface Modification To Reduce The Material Surface Energy And Enhance Condensation Heat Transfer

Studies have shown that in the solid surface achieve water vapor condensed beads arenecessary conditions of the surface has low surface energy, namely the solid surface willnot be or not easy to be the steam condensate fluid moist. So preparation can maintainlong condensed beads of low surface can realize the surface is condensed beads in actualindustry in industrialized application must first solve the problem. Due to the current inthe equipment of heat exchanger, heat transfer tube is still mainly of metal materials, andmetal materials generally has a high surface energy, which has a good wettability.Therefore, in order to obtain, must be on the metal surface of special processing changeits surface properties to reduce the surface energy to achieve water vapor on metalsurface in dropwise condensation. But so far, beads in industrialized applicationcondensation there has not been a breakthrough results. Laser surface treatmenttechnology, can be formed on the surface of the material with a certain thicknessprocessing layer, can make the surface microstructure refinement, fine structure, even inthe metal surface to form amorphous, effectively improve the surface properties ofmaterials. Laser application in the micro nano manufacturing is more and more widely.The research through laser surface modification of carbon steel, has built the condensateheat transfer contrast experiment platform, then contacted steam condensation test on thecontrast experiment under ordinary atmospheric pressure.Through the observation of the modified layer microstructure morphology, processedand analysised of condensation experimental data, and combined with the measuring thecontact angle of tube, studied the influences of microscopic characteristics of lasermodification, surface characteristics on condensation heat transfer characteristics.(1)Through the laser surface treatment tests found that: the grain of laser modificationlayer got more refined, the organization got more uniform, and micro hardness was improved greatly. The coating of modified tube1is thinner, melting district organizationwas close but quality is not good, there are some crack defects, etc. The coating ofmodified tube2was thicker, coating and matrix combined better.(2)Through the condensation heat transfer experiments found that the heat transfercoefficient of modification tube1is greatly raisedthan normal tube, and the heattransfer coefficient of modification tube2increased a little but not obvious. Further testsfound in certain conditions, with the increase of temperature and flow, the condensationcoefficient increases.(3)Through the contact angle measured found that contact angle of modified tube1outer surface was increased than the ordinary pipe, and, to some extent, reduced thematerial surface enegy, because of the appearance of the modified tube2surface is notsmoothness, contact angle is not easy to measure, and the surface roughness affect thesize of the contact angle, even the contact angle could measured,it could not be used asthe evaluation standard of the surface, so we did not measure it. All of these will providecertain basis and the reference with laser surface modification used in the research of heattransfer enhancement.