Drag reduction properties of superhydrophobic mesh pipes

Even with the recent extensive study into superhydrophobic surfaces, the fabrication of such surfaces on the inside walls of a pipe remains challenging. In this work we report a convenient bi-layered pipe design using a thin superhydrophobic metallic mesh formed into a tube, supported inside another pipe. A flow system was constructed to test the fabricated bi-layer pipeline, which allowed for different constant flow rates of water to be passed through the pipe, whilst the differential pressure was measured, from which the drag coefficient (f) and Reynolds numbers (Re) were calculated. Expected values of f were found for smooth glass pipes for the Reynolds number (Re) range 75010 000, in both the laminar and part of the turbulent regimes. Flow through plain meshes without the superhydrophobic coating were also measured over a similar range (750 < Re < 14 000). After applying the superhydrophobic coating, f was found for 4000 < Re < 14 000 and was found to be less than that of an uncoated mesh, but greater than that of a smooth glass pipe of the same diameter. This demonstrates that a superhydrophobic mesh can support a plastron and provide a drag reduction compared to a plain mesh, however, the plastron is progressively destroyed with use and in particular at higher flow rates.