The Relation Between the Nature of Pipe Wall and Frictional Drag

Experimental study is conducted on the characteristics of hydrolic frictional drag for lyophobic surface, with the surface consisting of polytetrafluoroethylene and the working media being water and 7^# machine oil. The test results indicate that, depending on the lyophobic performance of the lining material, the pipes lined with polytetrafluoroethylene have a better drag reducing effect than conventional steel pipes. A drag reduction of about 12% or 16% is achieved with the working medium being water and 7^# machine oil respectively, that is to say, polytetrafluoroethylene has a higher lyophobic performance against water than against 7^# machine oil. The theoretical analysis made on the flow mechanism of lyophobic surface shows that surface lyophobic treatment, which can lower the surface energy level to such a degree that the attraction of the solid wall on liquid molecules becomes weaker than the liquid molecular absorption, gives rise to gliding flow adjacent to the pipe wall, thus reducing the drag to a certain extent.