British teenage students have re-discovered a classical physical phenomenon, the Leidenfrost effect that could someday help ships glide through oceans more efficiently.
I'll let these 16 year old students explain it:
One day in Physics class we accidentally discovered you could get beautiful standing wave patterns on a drop of water on a very hot plate. This film gives an introduction to the wonderful Leidenfrost Effect.
The film was made by 16 students (aged around 16) - only three appear in the film, but everyone helped, as did their physics teacher. You can watch the video here.
Below I show a snapshot of the "beautiful standing waves."
The joy of discovery by these young students is clearly apparent; just beautiful. I highly recommend that you see the other short films produced by the Planet SciCast project.
From the students:
Right at the start of SciCast, we were looking for a slogan. Something that encapsulated what we hoped to achieve with the project, but also that explained it. I found myself typing 'Short films, real science', and we liked the shape of that so much it ended up in the rather dashing project logo. Hence, you see it everywhere, on posters and postcards, on the reports we send to our funders, on the pin-badges and T-shirts we have, and so on. It's up in the top corner of this page, I'll wager.
Thing is, it's never been quite true. 'Short films,' sure, but what's real about the science? Is a demonstration with a known outcome 'real science'? Surely 'real science' means experiment, observation, constructing theories, finding something new?
So I've always been a little nervous of our own slogan. It works in an arm-waving sense, but we've never had a whiff of 'real science' in the project.
This is an outstanding observation, thoroughly unexpected, and the reveal in the film is lovely. As it played in the awards ceremony I could hear mutterings of 'It's good, but why did it win?' -- replaced immediately by 'OK, that's why it won. Coooooooool!'
So what about those hot ships? Based on their observations, a warmer ship could pick up speed if the temperature of the hull is raised to use the Leidenfrost effect at strategic locations from bow to stern. Can this be exploited to save energy? Any Naval engineers out there wish to comment?
A recently published study in Physical Review Letters reveals that the Leidenfrost effect can be used to reduce drag in water by more than 85%!
According to the Abstract:
We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.
The effect is demonstrated below:
The Leidenfrost effect is a phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly.
Recommended reading from Philosophically Disturbed.
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Yes, but what the maritime world really needs is a lasting, non-toxic, anti-foul. ;-)
Heating the hull to 300c would be a pretty ultimate antifouling, no? And if you just heated sections as vapor generators, you could heat segments at different times, burning the crud off the bare metal. Yes, I know that would be crazy to implement. It might be interesting to see in a testing tank at small scale with induction heating though.
It would reduce drag, but how much power(heat) is needed to do this? At a minimum, I'd start with IR radiation, Stefan Boltmann tells you how much IR it will emit (transferring heat to the water), then what about the latent heat loses (vaporizing the water), and the conductive/convective loses. Not sure what the numbers are, but I'd be willing to bet several kilowatts per square meter of hot surface at a minumum. Then we have the fact that most ship drag is wave drag (the formation of waves which radiate the energy away). Incidentally the cure for wave drag is to submerge the vessel deep enough underwater that the amplitude of generated waves drops.
Thank you for your thoughtful comment.
if the point is to reduce drag by separating the hull and the sea from one another with a gaseous layer --- then the Soviet (now Russian) torpedo known as "shkval" comes to mind.
granted, it doesn't achieve this by means of boiling the ocean, nor does it travel along the surface of the sea. but the end result seems equivalent nevertheless.
Cool! It makes me wonder though, like #3 above, how much energy will be used in heating the hull. And what's the effect on marine life?