Researchers have developed a nanofur structure that significantly reduces fluid drag. For instance, consider the big amount of fuel used by the 90,000 ocean-going cargo ships that roam the seas (international shipping uses about 300 million metric tons of fuel and it is estimated it is responsible for 3.5% to 4% of all climate change emissions). Most of the energy in shipping is used to overcome surface friction.
Therefore an effective way to reduce frictional drag underwater could significantly reduce marine fuel consumption, thus making the shipping industry more efficient and environmental friendly. Additionally, in most applications which involve moving liquids through pipes and tubes of different sizes, a lot of the energy is used to overcome the drag the fluid experiences moving over the sidewalls.
Here as well, a drag reducing coating could compensate this effect and increase efficiency in these areas.Both the fern and the insect have surfaces covered by high density hairs which allow them to keep an air layer under water. This enables the Notonecta glauca bug to move nimbly and swiftly through the water by reducing the drag on its surface.
Scientists at the Institute for Microstructure Technology (IMT), Karlsruhe Institute of Technology, have developed a very inexpensive, highly scalable method to produce a superhydrophobic, air retaining biomimetic surface – a ‘nanofur’ – which shows not only a high long-term stability but also a high resistance against additional applied pressure. These properties enable the surface to significantly reduce the frictional drag experienced by fluids over a wide range of flow rates.
In experiments that tested the performance of nanofur coated surfaces, the measured pressure drop across the channels lined with nanofur is approximately 50% lower than in the channels lined with unstructured polymer – lower pressure drop for the nanofur indicates the reduction in fluid drag by the material, resulting from the air layer retained on its nano- and microstructured surface.
The nanofur is produced using a hot pulling technique, which was developed at the IMT. In contrast to other methods used to produce superhydrophobic, air retaining and drag reducing surfaces, the hot pulling method is very low-cost, because it uses sandblasted steel plates as molds, an inexpensive fabrication procedure and material. In addition, the process is highly scalable and uses no additional chemicals which could be toxic or harmful, thus making the nanofur easy to handle.
Read more at Nanowerk website: Bioinspired nanofur could significantly reduce underwater drag of marine vessels
Image Credit: Nanowerk
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