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Deeper understanding of nanobubbles could improve the design of ships’ propellers and cancer treatment

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Posted August 1, 2019

Ship propellers are like wheels on a car. They do experience a lot of stress and wear rather quickly. Imagine a part that is moving a 300 metre ship across the ocean – it is simply going to wear out eventually. Part of it are tiny little bubbles that form around the blades of the propeller. Now scientists from the University of Edinburgh found out more about how these tiny little bubbles form.

Tiny nanobubbles would look small next to a ship’s propeller, but they are powerful enough to take molecules of the metal away. Image credit: Hervé Cozanet via Wikimedia (CC BY-SA 3.0)

Ok, so ship’s propellers are actually losing metal as they are being used. Part of the problem is cavitation – tiny areas of vacuum appear as the propeller is pushing away the water. As bubbles form, they take away some particles of the metal of the propellers. This means that propellers are getting thinner and weaker as they spin pushing the ship forward. And that is a big issue, affecting both commercial and navy vessels. Tiny yet powerful nanobubbles are tens of thousands of times smaller than a pin head, but they are causing a lot of headache to engineers around the world.

Although cavitation is a well-known phenomenon, it is actually not very well understood. Especially in terms of the formation of the nanobubbles. Engineers now used the UK’s national supercomputer to launch some complex simulations of air bubbles in water to reveal the details of the growth of the nanobubbles. Supercomputer was needed, because scientists went as far as modelling the motion of atoms in the bubbles and observed how they grew in response to small drops in water pressure. These efforts were not fruitless – calculations revealed the critical pressure needed for bubble growth to become unstable. Interestingly, it is much lower than theory suggests.

The newly acquired information can be used to improve all kinds of engineering structures, including ships’ propellers. More interestingly nanotechnologies could be developed to harness the power of thousands of jets from collapsing nanobubbles. This could be useful in novel cancer therapies, or for cleaning high-precision technical equipment. Duncan Dockar, one of the authors of the study, said: “Bubbles routinely form and burst on surfaces that move through fluids and the resulting wear can cause drag and critical damage. We hope our insights, made possible with complex computing, can help limit the impact on machine performance and enable future technologies”.

Slow motion cameras and supercomputers will accelerate the research into such minute phenomena as nanobubbles of cavitation. Hopefully, this will allow creating new shapes of ship propellers. But it is interesting that scientists are seeing those nanobubbles as opportunity as well – someday they may help destroying cancer cells.

 

Source: University of Edinburgh

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