A hot body could help ships reduce drag

New research into drag reduction has the potential to help industries such shipping to reduce energy use and carbon emissions.

Professor Derek Chan from the University of Melbourne's Department of Mathematics and Statistics said the research demonstrates a new way to minimise drag of fast moving projectiles in water.

A collaboration between the University of Melbourne and the King Abdulla University of Science and Technology in Saudi Arabia, the research was based on the 255 year-old Leidenfrost effect.

The Leidenfrost effect describes the phenomenon where a liquid produces an insulating vapour layer when it comes in contact with a that is hotter than its boiling point.

The new research used high-speed video footage to assess the drag produced from polished balls dropped into liquid. The results found that the drag on the ball is reduced to almost the minimum possible through the creating of an insulating vapour as it falls through the liquid.

Professor Chan said that the new drag reduction method has the potential to reduce energy costs for a broad range of applications, such as ocean transport and high-pressure pumping of liquid through pipelines.

"An obvious area of application is shipping," he said.

"Australia transports a large amount of products such as and grain around the world. The ship's hot body could substantially minimise the amount of drag as it passes through water, therefore potentially reducing transportation costs and ."

"There are still a number of issues that need to be addressed before this drag reduction method can be applied commercially, such as the effect of increased heat on issues such as corrosion," he said.

The paper was published as a research highlight in today, and in full by the , a peer-reviewed scientific journal published by the American Physical Society.

The University of Melbourne and the King Abdulla University are now writing a follow-up theory paper. While the first paper demonstrated that the drag reduction method is real and achievable, the follow-up paper will provide detailed theoretical analysis of the research.

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Citation: A hot body could help ships reduce drag (2011, June 2) retrieved 23 August 2019 from https://phys.org/news/2011-06-hot-body-ships.html
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Jun 02, 2011
"There are still a number of issues that need to be addressed before this drag reduction method can be applied commercially, such as the effect of increased heat on issues such as corrosion," he said.

Ya think? Maybe one should also calculate exactly how much heating a shipping vessel up is going to cost before we start talking "savings"?

Jun 02, 2011

Do you have any idea how much energy it is going to take to heat the entire hull or a cargo carrier to the boil point! WAY WAY WAY More energy than any drag reduction measure can make up; you would be continuously boiling off the heat, so continuous heating would be required. Not to mention the ship would probably be uninhabitable and the heat will probably affect the cargo, possibly causing high pressure tanks or oil to explode, possibly causing food to rot faster.

This isn't research, it's plagarism (this has been studied in full before and found to be uneconomical, obviously)

Jun 03, 2011
It's too bad you use the T word so often, Vendicar, because it forces me to rank you with a 1. In the future, I'll probably just report them as abuse.

Jun 03, 2011
Gunslingor1, have you ever heard of insulation? Claims that the whole ship would have to be heated are patently absurd. If you think about, not even the hull would need to be heated evenly. Most of the heat would need to be released from the bow and keel. Because the fluid flow sweeps from front to back and because the water vapor bubbles would rise, the steam bubbles and hot water would be swept back and up along the hull. Thus the rest of the hull would need less heating to keep this water at the boiling point. As the bow is where much of the friction occurs, it may be that the rest of the hull doesn't even need a "steam jacket," limiting the need for heating to a small area. And let's not forget the engine is producing waste heat anyway, and what better way to get rid of it than water cooling...

Jun 03, 2011
Wouldn't this seriously affect the buoyancy of the ship as well? The ship would sink like a rock if it was boiling the water touching its hull.

Jun 03, 2011
I wouldnt think so Jav. Your replacing water as fast as you can boil it.

However, I'd also guess this is based on the initial drag from the ball, not the final as it's going to cool rapidly in the liquid.

Frankly, even with barakn mentioning recycling exhaust heat, the amount of energy required to heat it up to be effective, even over a small area with great surface area, doesnt seem to be economically feasible. Now if there's a medium between boiling and just being warm that may be a different story, but they didn't offer any scale or suggestion of such in their test, much less what liquid it was in.

Salt water isn't great on steel in the first place, heating up the steel, may definitely add some physical problems.

Jun 04, 2011
This is just a ridiculous idea ... Heating even a thin, insulated panel on the hull of a ship would require a retarded amount of energy.

Jun 05, 2011
While it reduces drag, it also negates lift - i.e. your boat will just sink immediately if you apply this all over the hull.

Jun 05, 2011
A. The ship will not sink. The vapor layer will actually increase the volume in the water slightly and increase buoyancy.
B. The entire hull does not need to be heated, only strips. The vapor layer will spread along the hull.
C. This is similar to tests done years ago with compressed air to form the layer.

And yes, I am an engineer and former Naval Officer.

Jun 05, 2011
Then why heat it and not use cavitation bubbles form ultrasonic speakers (just like in fog machines)? A lot less energy needed for that.

But seeing as ships that encounter bubbles (e.g. methane bubbles or drill-ships directly above a blowout) sink I don't see how this will work unless we radically change ship design (flat bottoms and vertical sides with the aereation from Leydenfrost/ultrasonics only on the sides)

If you areate water you reduce buoyancy. That's pretty much the problem.

Jun 05, 2011
I think you need some kind of skin effect. Have you ever seen water droplets not evaporate quickly on a wood stove or hot plate surface and remain suspended on a thin vapor of steam for a period of time. ( similar inverse properties ), I'm not sure of the energy calculations involved with this observation, perhaps others can extrapolate further. And, review the successful Russian shkval torpedo technology which offers submersible possibilities. Perhaps, nuclear power or future fusion reactor could provide the energy required.

Jun 06, 2011

How would that affect hull integrity though, when heating strips of the hull? Would it weaken the materials?

Jun 08, 2011
I wouldnt think so Jav. Your replacing water as fast as you can boil it.

Maybe I'm misunderstanding, but isn't buoyancy dependent on the density of the water relative to the overall density of the ship (I'm referring to if the whole hull were heated)?

Since you're boiling the water away, the density local to the ship's hull would decrease, causing the ship to sink a very small amount until it contacted more water (with enough density to allow the ship to float again), which would then be boiled off, etc... Eventually the ship would sink, no?

Jun 08, 2011
A. The ship will not sink. The vapor layer will actually increase the volume in the water slightly and increase buoyancy.

So the volume would increase since steam is significantly less dense than water, but wouldn't the steam quickly diffuse through the water rather than exerting a force on the hull? The fluid would flow from high pressure (point of boiling) to low pressure (away from the hull). A ship is buoyant when it takes more force to push all of the water out from under the ship than it does to hold it up. When you boil the water, you make it easier to push the water (now steam) away, lowering the buoyancy.

I could see this potentially working with strips on the hull, but the more hull that is boiling water away the lower the buoyancy would be. Now you're building bigger ships that have to weigh less or have to carry less cargo.

I'm still not sold on this being a good idea.

Jun 08, 2011
Basically, buoyancy is just drag in the "up" direction. If you reduce drag, you reduce buoyancy.

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