Fabrication Of Superhydrophobic Film And Study Of Gas Liquid Two Phase Flow

Superhydrophobic film has been successfully prepared on glass substrate by sol-gel method.Specially,the stable and transparent alumina sol was used for film coating.The gel film was immersed in boiling water,and then the network-like rough structure was formed. Subsequently,the rough surface was modified with fluoroalkylsilane.With the measurement of video-optics contact angle tester,the largest water contact angle on the film is 168.3°,and the contact angle hysteresis is about 5°.The prepared films are characterized by means of scanning electron microscopy.It is found that the surface of the film before immersion in boiling water obviously presents a smooth blocky structure.After immersion in boiling water for 10 min,the film presents a network-like rough structure which is of micro-nano grade.The experimental results demonstrate that the surface micro-structure is the key to the preparation of superhydrophobic surface.Effects of different parameters on sol state are also investigated.And base on the analysis of chemical composition of the superhydrophobic film,we propose the mechanism of the formation of the microstructure.In addition,the visible transparency and self-cleaning properties of the films are discussed.Experiments of air-water two phase flow are performed in 1～5mm I.D hydrophilic and hydrophobic micro/mini tubes,respectively.The experimental results together with large amounts of observation judgment are used to ascertain the flow patterns in hydrophilic and hydrophobic tubes.Flow pattern transition was described in detail and flow maps were drawn, respectively.The effects of diameter and wettability on the flow pattern transition are discussed. Compared with reported results,the flow pattern maps drawn in present study coincide basically with the published flow pattern map in micro/mini tubes.However there exists a significant difference between our flow pattern map and previous results in common big tube. Furthermore,distinguishing flow patterns by pressure drop fluctuation was attempted.The result shows that the flow patterns distinguished by the pressure drop fluctuation are consistent with observation method.