High-Tech Electro-Defroster

DahBaker writes to mention a News.com story about an ingenious way to de-ice a surface. From the article: "Dartmouth College engineering professor Victor Petrenko, not to be confused with one of the Champions on Ice, has devised a way to use a burst of electricity to remove ice caked on walls or windows. For surfaces coated with a special film, the jolt gets rid of ice in less than a second, far less time than it takes to hack at it with an ice scraper. While drivers might find easy-cleaning windshields convenient, the technology--called thin-film pulse electrothermal de-icing, or PETD--could have significant economic impact if widely deployed. It could, for example, cut the costs of repairing power lines downed by ice storms and keep plane windshields frost-free, decreasing fuel consumption."

Re:Not just plane windshields

[aibrahim]

Maybe instead of "thinking" about the issue you should have checked out the company site where they have a video of ice being removed from an airfoil in a wind tunnel [iceengineering.com].

That seemed like a fairly conclusive demonstration of the practicality of this process for that purpose.

Now where is that damn pretty floral bonnet of mine...

Re:Not just plane windshields

[darthwader]

(deploying the boots early can result in the ice simply forming around the shape of the inflated boots, rather than their deflated shape, rendering the boots ineffective.)

I really hope that no pilots are getting their flying advice from slashdot (just like no lawyers are getting legal advice here), but just in case: the latest research indicates that ice bridging is a myth, and you should use the boots as soon as you detect any icing, rather than waiting for build-up.

http://www.aopa.org/pilot/features/inflight9910.ht ml [aopa.org], http://www.elliottaviation.com/wavelink/1999q1/wav art21.asp [elliottaviation.com] and http://www.faa.gov/library/manuals/examiners_inspe ctors/8400/fsat/media/fsat9818.doc [faa.gov] are good references.

http://www.pilotfriend.com/safe/safety/icing_condi tions.htm [pilotfriend.com] is a great article about all sorts of aircraft de-icing and anti-icing methods.

Re:Does this quote from TFA sound like BS?

[Manchot]

Well, this New Scientist article [newscientist.com] from 2002 is also about Victor Petrenko, and goes into a little more depth.
 
Apparently, it is is the protons which are the majority charge carrier. If you remember your high school chemistry, there exists a small amount of hydrogen and hydroxl ions even in water with a pH of 7. Presumably, ice, which is a crystalline version of water, also has a small concentration of hydrogen and hydroxyl ions. According to the article, the free hydrogen ions (a.k.a. protons) travel between the crystalline structure of the ice, carrying current. I would guess that the hydroxyl ions don't do the same thing simply because they are much larger than hydrogen ions, and are effectively immobile in the lattice.

Re:Not just plane windshields

[aibrahim]

I can see that being an ass generates a pile of interest. It unfortunately doesn't engender any actual reasoning, just more "thinking." You people are intellectually lazy.

Maybe I should try leading by example instead.

The key is that the GP says power, but he is really talking about energy budgets. This thing needs power over a very short time. Not a huge pile of energy.

How much energy... How about a calculation... oh dear is that sort of thing even possible on /. ? I'll try anyways. One caveat, whenever I trot out numbers: I *insist* you double check before believing them.

Lets pretend we are de-icing the entire surface area of a 747-400D, 541.2m^2. This is a huge overestimate of our work loads, because we really only have to defrost the leading edges and a foot or two back.

The C|Net article linked says he only needs to melt a micron or two for it to work, so we'll aim for three microns, or 3*10^-6 meters.

Ladies and gentlemen the total volume of water we are talking about over that vast area with the assumptions I have made is 1.6 mm^3. That is only about .146 grams of water.

That means we must expend .146 calories people. That's .611 joules.

You think a plane of any sort can spare lets say 611 joules, enough energy to de-ice the wings of a 747 a thousand times a flight ?

If you really think they don't have the energy budget, maybe we can just stick a D-Cell battery on board. Of course that's overkill because a D-Cell stores 10000 joules.

What about efficiency ? According to Petrenko's site at Dartmouth [dartmouth.edu] the system is wastes almost zero heat energy because of the short time over which it operates. Basically there is no time for it to go anywhere else.

You think we can somehow draw such a tiny amount of energy on even the flimsiest Cessna ? If not, I'm not getting into the damn thing.

In any case, it turns out Goodrich Aerospace has had good results flight testing the system on propeller driven aircraft, and is preparing to flight test it on jets. No details I got that from Petrenko's page at Dartmouth too.

Are you all starting to understand how cool this technology is ?

Re:Not just plane windshields

[ipfwadm]

Someone else already pointed out your obvious mistake in converting cubic meters to cubic millimeters, but that's not the only error...

the total volume of water we are talking about over that vast area with the assumptions I have made is 1.6 mm^3. That is only about .146 grams of water.

Isn't one of the supposed beauties of the metric system that you can deal with powers of 10? So how can it possibly be the case that 1.6 cubic millimeters is equivalent to .146 grams? That would be a factor of 10.9589. Of course, even if we were to use a factor of 10 we'd still be wrong since you again screwed up the conversion due to not working in three dimensions: there are 1000 cubic millimeters in a cubic centimeter, not 10. So if the starting number were really 1.6mm^3 (which it's not as the other poster pointed out), that would equate to 0.0016 grams of water, not 0.16, and certainly not 0.146.

So, combining the original screw-up (which made your number low by a factor of a million) with this one (which made you high by a factor of a hundred), as well as your whacked out mm^3 -> gram conversion (which made you low by 10%), the final answer should be... about 6.8 kJ. Or 6.8 MJ if you want to do it a thousand times in a flight.

But wait, there's more! You're assuming that the temperature of the ice needs only be raised by 1 degree C. The article says it needs to be raised TO 1 or 2 degrees C, but who knows what the starting temperature of an iced-up wing is. But let's say we need to raise it 5 degrees. Now we're up to 34 kJ.

But wait, there's STILL more -- and this one's a biggie! You're (conveniently) ignoring heat of fusion. Remember that from chemistry class? So tack on another 334 joules per gram of water. At 1600 grams, that's another 534kJ every time you fire off this thing, for a grand total of 567kJ per use, or so many megajoules if it's used 1000 times in a flight. Not gonna de-ice a 747 with a D cell anymore, are we?

And just as an aside, 541 meters^2 isn't as big an overestimation as it may seem at first glance, because that is not the "total surface area" of the wings, it is the wing area. You'd need to multiply 541 by 2 to get the total wing surface area, as wings have two sides - you know, a top and a bottom. You may even need to multiply it by a little more than 2 since I'm assuming wing area is just the area of the wing's planform, and not actual surface area which would be higher due to the airfoil shape, but I'm not an aeronautical engineer so I don't know.

Don't post innacurate information

How about your hideously wrong math, does that count as inaccurate information? And what about your hideously wrong spelling of inaccurate?