Font Size: a A A

Study Of Preparation And Drag Reducing Properties Of Nano SiO2/PVDF Hydrophobic Coating

Posted on:2013-01-24Degree:MasterType:Thesis
Country:ChinaCandidate:W J ZhangFull Text:PDF
GTID:2211330371460319Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
Low energy surface method is a effective method to reduce the fluid friction. By reducing the surface energy, the surface of the object could have a very weak wall affinity with fluid, which will decrease the velocity gradient and reduce the surface shear stress. The turbulent boundary layer becomes thicker, and the turning point is postponed, as a result, fluid friction is reducd. Low energy surface coating can not only decrease drag reduction, prevent surface pollution of the ships, but also can apply to the inside surface of the pipeline, to reduce the energy consumption during the transportation and prevent pipeline blockage. So the coating has wide application range in defense and industry.In this paper, SiO2 particles prepared by the stober method, one sort of sol-gel method, was added to PVDF, so that the coating structure on the steel disc was similar to the lotus leaf surface. The structure of the SiO2 coating can further reduce the surface energy. Infrared absorption spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) analysis was done to the SiO2 particles; use optical microscopy, scanning electron microscopy to observe and analyze the surface morphology of the coating. Contact angles were measured by using JC2000X contact angle detector; use rotating disc-drag test apparatus to test underwater drag reduction performance; and test the different drag reduction performance of the hydrophobic coating which have different components.The FT-IR analysis showed the SiO2 particles was high purity and without by-products. The XRD analysis showed that the structure of SiO2 microspheres was amorphous. SEM image showed that the SiO2 particles had no significant particle agglomeration, and the particle diameter was small. The SEM image of the coating surface showed it was uniformly distributed, had uniform morphology and bionic micro-rough structure. The contact angle of the hydrophobic coating can reach 133°. And the drag reduction test showed, with the SiO2 coating hydrophobic angle increase, drag reduction effect was gradually increasing; drag reduction effect of the coating was conspicuous not only at low Reynolds numbers but also at high Reynolds number. At low Reynolds number (0.04×106-0.16×106) the drag reduction effect was better, the drag reduction rate was up to 57.6%, at high Reynolds number (0.8×106), same samples can still keep 20% of the drag reduction rate. The drag reduction can be effected by the SiO2 particle size and the amount of the particles. And drag reduction effect was better when the particle size was smaller, the amount of SiO2 was 0.6g. The coating had a certain durability, after long-time water immersion, the drag reduction rate only dropped about 5%.
Keywords/Search Tags:low energy surface, hydrophobic coating, SiO2, PVDF, underwater drag reduction, rotating disc-drag test apparatus
PDF Full Text Request
Related items