Hot bodies no drag

May 27, 2011

( -- A Swinburne University professor was part of a team that showed that drag on hot bodies moving through liquid can be radically reduced by up to 85 per cent, potentially doubling their speed.

In an experiment highlighted by the world's top physics journal, , researchers Ivan Vakarelski and Derek Chan observed that a heated ball can fall through liquid more than twice as fast as a colder, ‘control' ball.

The discovery exploits the drag-reducing properties of a vapour layer formed between a hot body and surrounding liquid, known as the Leidenfrost effect.

"A very hot body - hot enough to vaporise the thin layer of liquid in contact with it - can drastically reduce energy-sapping drag forces when such bodies travel at high speed through the ", said Swinburne physicist Professor Derek Chan.

This is a novel application of the familiar phenomenon where water drops are observed to dance or ‘levitate' around when splashed onto a very hot plate; known for over 200 years as the Leidenfrost effect.

Partly funded by the Australian Research Council, the research was purely fundamental in nature, but may have potential military applications.

Chan - an already distinguished ARC principal investigator working in the area of surface science at the nano-scale - stressed the genesis of the discovery was motivated by novel science.

"This is a novel use of an idea that has been around for over 200 years. We did not set out to do the research with any particular application in mind. We were just curious about a new possibility. But we welcome technologists taking it on and developing it further."

However he conceded it could have military applications, such as helping to make submarines, torpedoes and even sea-launched missiles drastically swifter for short periods.

"But this is really very fundamental research and I see the possibility of broader applications in efficient energy usage. For example allowing marine vehicles to travel faster and further for the same amount of energy or power, and ultimately contribute to reducing greenhouse gas emissions," he said.

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More information: Drag Reduction by Leidenfrost Vapor Layers, Phys. Rev. Lett. 106, 214501 (2011) DOI:10.1103/PhysRevLett.106.214501

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.

Provided by Swinburne University of Technology

5 /5 (1 vote)

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not rated yet May 27, 2011
This is essentially the WHY of a ultrasonically tipped torpedo that travels far faster than it's traditional counterpart.

Also, there is a hydrogen production method that recently evolved in Japan, based on 'brown's gas' production techniques. Like Stan Mayer's Brown's gas devices, it essentially uses ultrasonic excitation to double and even triple system output for the given watt input.

Maxwell's original math said (before Morgan paid to have it edited):Asymmetrical, and ELASTIC.

Find Maxwell's original math and treatsie, and -----it will be right there.
not rated yet May 27, 2011
Find Maxwell's original math and treatsie, and -----it will be right there.

Interesting stuff. So can this be found in any one of James Clerk Maxwells books on Amazon or is there one you recommend over others?
1 / 5 (1) May 27, 2011
So how much does the energy usage of making the projectile hot, offset the energy usage of overcoming the drag and getting to that speed by using pure motive power?
1 / 5 (1) May 27, 2011
They're right that the idea has been around a long time (although I didn't know it was 200 years). Nearly 30 years ago I learned in college that the Soviets had developed (or were "actively developing" - I don't remember which) torpedoes powered by vented rockets - where most of the thrust went out the back as one would expect, but where a small portion was redirected to vent forward off the nose. The small counter-thrust was fantastically more than offset by the drag reduction of the torpedo moving through vapor rather than water. I wonder what became of those things...
not rated yet May 28, 2011
Find Maxwell's original math and treatsie, and -----it will be right there.

Interesting stuff. So can this be found in any one of James Clerk Maxwells books on Amazon or is there one you recommend over others?


You will not find the original works in any modern book. They were collected and destroyed by the publishing firm that was owned by J.P. Morgan, when he hired Lorentz (lorenz?-there are two involved--with slightly different spelling) to go on a book tour..and he paid to have them all removed and replaced in any place where they were found. collections, libraries, schools, the whole lot.
1 / 5 (1) May 31, 2011
Thks. What is the nature of this asymmetry? Is it clausal in nature?