h a l f b a k e r yQuis custodiet the custard?
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Recent developments have made it fairly easy to apply a microscopic layer of diamond-structured carbon to a wide variety of materials. The process is done in a vacuum, with a carbon-rich gas, and the layer is "grown".
Because diamond is the hardest so-far-known ordinary material, drill bits and
other cutting tools have been the first things to receive the diamond-coating treatment. Not so long ago I bought a coated circular-saw blade for about $9, so not only is the coating process workable, it's also affordable.
Well, did you know that ALSO because diamond is the hardest substance, it is best solid heat conducting substance? The reason why is because heat-vibrations are "seen" by diamond just the same as sound-wave vibrations. So heat at Point A literally gets conducted to Point B at the speed of sound inside diamond (thousands of meters per second).
Therefore, I suggest that a particular suitable other use for diamond coatings is in heat-exchangers in harsh environments. For example, in seawater desalination plants, salt-water corrosion is a major problem with common aluminum heat exchangers. Sure, I know that they can use special ion traps as part of pre-filtering the water being desalted, but those filters have to be refreshed (regular extra expenses in running the plant). So, coat the aluminum with diamond (rather inert, chemically, not to mention being "non-stick" as well!), and not only do we protect the metal, we also greatly increase the surface area of heat-exchange (that microscopic coating is not hardly smooth!).
Machine to apply diamond coatings to stuff
http://www.sp3inc.com/600reac3.pdf
I'm sure they'll be happy to sell you one, but this model is a bit small for the Idea proposed here. [Vernon, Oct 04 2004]
Quite of variety of things can be coated.
http://www.advanced...02/exploringamt.htm
I see they use carbon dioxide as the carbon source here. Cool! (a minor way to reduce CO2 buildup in the atmosphere :) [Vernon, Oct 04 2004]
Many uses for diamond coatings
http://www.ddk.com/...in%20Freiburg-1.pdf
Smooth finish [Ling, Oct 04 2004]
U.S. Pat. 6,205,291
http://164.195.100....48&RS=REF/5,461,648
Scale-inhibiting heating element and method of making same [ldischler, Oct 04 2004]
[link]
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OK, so will this diamond coating
stick to everything you throw at
it? I know you can sublimate
diamond on a suitable
diamond-like lattice, but will it
bond to any metal lattice, or will
it just form graphite in those
cases? And will the thermal
expansion of the metal not peel of
the diamond layer after repeated
heating and cooling? |
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Steam engines usually de-gas
their water flowing into he boiler
by bulling steam through it, so
the oxygen(gas) will not eat away
the boiler. That sounds like a
better solution to me than a
deBeers induced coating ;-)
(the other solution is reverse
osmosis as used in ocean going
yachts) |
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all in all, sorry, I hope you like
fish. |
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nietch, I didn't say that this Idea was suited for all occasions. High-temperature environments may even cause breakdown of the diamond to graphite. The desalination I mentioned isn't done at the kind of temperatures used in steam engines. |
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Another moderate use would be in air conditioning systems near seawater. The "salt air" does a horrible amount of damage to aluminum, including the heat-exchange-fins on air conditioners. But give them a diamond coating.... |
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//will the thermal expansion of the metal // That's an interesting point. How do they keep that from happening with tools? Seems like it would be a big problem, but if they can fix it for tools they can fix it for other technologies. Actually, in low pressure difference situations you may not need the metal at all. |
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P.Diddy would love this one. |
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Had a quick rummage through Google, and found some interesting things:
Diamond has a speed of sound of approx 17,500m/s.
It attracts grease, but repels water.
It's hardness cannot be accurately measured, since it is measured by impaction with another diamond.
It has approx 5 times the thermal conductivity of copper (but varies according to purity and temperature, peaking at 77K).
So there. |
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Worldgineer, I'm thinking that the diamond doesn't get any hotter than the drill bit core (conducts heat so well). I might be mistaken about actual temperature needed for diamond to degrade to graphite; it may be higher than I first thought. |
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Regarding heat expansion, it may be that simply because it is a thin layer, it can expand in the 3rd dimension without stressing the other two. |
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That's going to be a very big vacuum chamber |
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I use sintered hard metal diamond coated custom drills
on my drilling machines and man,do they work. Diamond "grane" I use is very small, about 1 micron. It's incredibly smooth and slippery. It solved all my problems of heat transfer and material buildup on the cutting edges. I'm drilling carbon fiber/titanium/carbon fiber/aluminium, all stacked
toghether, on a single operation, at a rate of ten
holes/minute (a 5 mm dia.).Diameter tolerance is some twenty microns. No problems at all, drill bit lasts
some 1200 holes. With HSS drill I manage 1 (one) hole. A long way... |
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That's some composite sandwich there, what are you making? |
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[Vernon]://The desalination I
mentioned
isn't done at the kind of
temperatures used in steam
engines//
Then cathodic protection should
much easier to do. Just attach
some magnesium sacrificial
annodes to it and you are done.
No need to add another layer to
your heat exchanger.
As for airco unit in salty
environments: the heat
conducting properties of a
diamond layer a couple of
nanometers thick will not
influence the heat conducting
properties of a piece of
aluminium a million times
thicker.
And that goes for all other uses
where you want to use a
nanoscale thin layer to improve
heat conductivity. And as a
paint, it is really expensive. I
guess you really can only use it
for its hard durable surface... |
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Non-stick eh... time for the diamond-coated wok to make its infomercial debut. Also the diamond-coated ginsu knives |
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nietsch, you might notice that in the main text of the Idea I did mention the use of special ion traps (otherwise known as sacrificial anodes), and you are NOT "done" by using them. Because they have to be replaced, again and again and again.... I see adding that microthin (not nanothin) layer as being a better deal in the long run. |
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With regard to the aluminum being a million times thicker than the corrosion-protective coating, well, that's probably an exaggeration. Still, I see what you are saying, but have a couple of doubts. |
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For starters, while I see a couple of posts and links indicating that diamond coatings can be extremely smooth, it is my understanding that when these coatings were first developed, they were far from smooth. THAT kind of coating would indeed increase the exposed surface area of the aluminum. While this cannot improve the rate at which heat can travel THROUGH the aluminum, it can allow the heat that does go through to enter the surrounding medium more easily. The better efficiency that I originally envisioned may not be as much as I expected, but I think it will be a little greater than zero. |
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Next, keep in mind that as aluminum tubing enters a heat exchanger, the hottest fluid in the tubing is at that place. Well, a diamond coating can transport heat down the length of the outside of the tubing faster than the fluid inside can flow through it. This also should mean some efficiency increase, in exchanging heat with the surrounding medium. I do acknowledge that this effect will depend a great deal on the thickness of the coating. But, if a thicker coating is better, why SHOULDN'T such be applied? ($$$ of course; some will not care.) |
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(scubadooper) 737 rudder. Or rather, the machine that drills it. |
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[Vernon]://special ion traps as
part of pre-filtering the water// |
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sounds as ion exchange to me,
not sacrificial annode. Yes you
have to change them regularly.
you can minimise oxidation with
paint. A few microns of paint will
(again, but to a lesser extend) not
change the heat conducting
properties much. But if you want
a really good cunducting heat
exchanger, i suggest to use pure
diamond. Otherwise this peg is
for square holes... |
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Cool, are you in Seattle then? I visited Seattle once, amazing to see so many aircraft under one roof. |
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nietsch, regarding "ion traps", I chose that phrase to attempt to cover more than one possible way of inhibiting corrosion. A sacrificial anode DOES directly attract/trap certain ions, after all. And paint doesn't last as long as diamond, as you know. |
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Regarding all-diamond, well, I originally thought about specifying making the radiators out of material so thin (easier to make than something from diamond, see?) that after being heavily coated, inside and out, then the thing would qualify as being mostly diamond. BUT, for all its hardness, diamond likely lacks sufficient physical strength to be the main load-bearing material for the pressures inside heat exchangers. Too brittle, unless the coatings are prohibitively ($$) thick. |
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(scubadooper) No, I'm a Spaniard and I live in Guillena, at the Sevilla Northern Mountains, the most remote and isolated mountain village you can imagine
(the hungry wolves eat all the telephone wires). |
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Congratulations [Vernon] for producing a short idea! |
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As for the idea itself, you will get a negligible increase in heat transfer rates by coating your heat exchanger with diamond. Most of the resistance to heat transfer will be in the fluid boundary layers on either side of the tube, and since the increase in surface roughness will be on a micron scale the coating will not alter the boundary layer significantly. In fact I would worry that the rough surface might allow fouling materials to attach to the tubes, increasing maintenance requirements. However the idea of a hard, durable, heat and chemical resistant coating is a good one, particularly for harsh applications (e.g. sulphuric acid production?) where exotic metals such as titanium have to be used at the moment. |
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diamond coating for the heat exchanger would only increase speed of the heat exchange, not the gross heat exchange, which is usually accomplished by large surface area anyway. custom diamond shapes are also relatively expensive to produce, coating and flat pieces are easy, but try to get direct fluid to diamond to fluid contact and you'll need a minimum 30micron thick 30cm diameter diamond plate, and those cost about $8, on top of that, you'll have to incorporate it into the heat exchanger - not very cost effective |
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[Finflazo] In my work as a glazier we did some work at the airport and were give some long 1/2 inch chuck 3/8th inch "Boeing Bits" they were called. |
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They drilled through akuminum like it was wood. |
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It was the first and last time I fell in love with a bit. |
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The "speed-of-sound" reference is a little misleading. Certainly the time lag between application of heat to one side of the material, and the first increase in temperature on the other side, is determined by the speed of sound in the material, but the temperature rise at that time is infinitesimally small. |
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Consider, for instance, that the speed of sound in steel is 6km/s. Put the end of a 20cm spoon in a gas flame at 500C; the first vibrations will reach you after 3E-05 seconds, yet you can still hold the spoon 5 seconds later. |
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Not important to the idea; I'm just clarifying/being pedantic. |
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[david scothern] in steel heat is NOT transferred at the speed of sound in the material. This phenomenon is only true of very hard materials like diamond. |
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So if a thick diamond conductive layer was installed all around an orbital device, then perhaps the heat on re-entry could be conducted to the rear almost as fast as it arrives at the front. |
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[Ling], yes, but there are two problems with that particular use. First is, after you have conducted the heat to the back of the vehical, then what? The heat still has to be transferred elsewhere to cool the craft, and the craft is SURROUNDED by a hot sheath of plasma. |
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Second, diamond BURNS in oxygen, when heated enough, just like coal. |
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I was thinking that the rear would be in a partial vacuum, and so it would be cooler, and if the diamonds could conduct the heat away, they wouldn't heat up enough to burn. |
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You don't conduct heat into a vacuum. Heat has to be radiated into a vacuum. I know you said "partial vacuum" but the more closely it resembles a vacuum, the more you have to radiate instead of conduct. Personally, I think existing heat shield technology for re-entry is adequate. Those tiles on the Shuttle simply RESIST being affected by the heat they acquire, and cool very quickly when encountering cool air. |
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I think you've overlooked something. The time it takes to transfer heat the ZERO distance between the heat source and the exchanger is ZERO (well zeroish). Anything between the heat source and the exchanger will be in the way and increase transfer time. |
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However, this is probably still a good coating to reduce corrosion without significantly reducing heat transfer. |
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//It attracts grease, but repels water.// If this is true at the atomic level, it might reduce heat transfer from water. |
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I read where a hot carbon monoxide gas was used to make diamond disc in a chemical reaction chamber. So it may be possible. |
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