The Fanless Spinning Heatsink 380
An anonymous reader writes "There's a fundamental flaw with fan-and-heatsink cooling systems: no matter how hard the fan blows, a boundary layer of motionless, highly-insulating air remains on the heatsink. You can increase the size of the heatsink and you can blow more air, but ultimately the boundary layer prevents the system from being efficient. But what if you did away with the fan? What if the heatsink itself rotated? Well, believe it or not, rotating the heat exchanger obliterates the boundary layer, removes the need for a fan, and it's so efficient that it can operate at low and very quiet speeds. That's exactly what the Air Bearing Heat Exchanger, developed by Jeff Koplow of the Sandia National Laboratories, has developed. It's even intrinsically immune to the build up of dust and detritus!"
Fanless doesn't seem to be an accurate description (Score:4, Insightful)
Fanless or Not, .. (Score:2)
.. it seems like a great invention, trully ground-breaking if it works. All we have to do now is wait for the patent wars to be over (suddenly $BigCorp and $PatentTroll "discover that this infringes on their innovations somehow and some such"), and by 2054 this will be a commonplace in cooling.
Now I wander if the guy was under contract- if he was, he will probably get nothing but his salary out of it. One of my friends is family with the guy that invented the dictionary in cellphones; but since he was under
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From TFA, highlighted for your convenience...
The cooler consists of a static metal baseplate, which is connected to the CPU, GPU, or other hot object , and a finned, rotating heat exchanger that are cushioned by a thin (0.001-inch) layer of air. As the metal blades spin, centrifugal force kicks up the air and throws it up and outwards, much like an impeller, creating a cooling effect.
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Seems like this concept would already have been dealt with via spinning hard disk platters, but those don't weigh nearly as much as a heat sink and are segmented out specially with shock absorbers in the HD enclosure.
Re:Fanless doesn't seem to be an accurate descript (Score:4, Informative)
The bearing between the fan and the plate is a very small air gap. Because it's small, and because it's constantly being churned around, it's thermal resistance is low.
Because the movement fan part destroys the normal zone of still air around radiator fins it dissipates heat more quickly and efficiently.
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you thought wrong, they use standard box fans or squirrel cages
Re:Fanless doesn't seem to be an accurate descript (Score:5, Funny)
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LOL yes I forgot about that part
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yea filters get clogged, and I really dont by the immunity thing, yes it may not get compacted tween a fan and the top of a heat sink but it seems like the fins of this thing would be just as easy to clog since your passing dirty fluid tween small spaces
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That "boundary layer" theory is well justified by models and experiments. The lack of a fan does not make it disapear, but rotating the heat sink does make it smaller.
About dust, it only accumulates over a hight speed rotating surface (where the air speed is increasing) up to a certain amount. That amount is certainly way lower than the dust that accumulates at a static place where the air speed drops. Immune do dust is a justfied simplification, altough a bit over confident.
Also, I completely agree with yo
I'm curious... (Score:2)
Doesn't there still need to be a stationary connection to the rotating heatsink since the CPU is stationary? And if that's the case, how does this help prevent the boundary layer? Seems like one would still be able to form between the CPU surface the the rotating heatsink.
I'm no scientist, however, so I'm probably making a false assumption. But I am curious how this alleviates that boundary layer...
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The article and the PDF will answer all your questions.
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LoB
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Essentially, they claim the really thin (~0.03mm) layer of air between the stationary plate and the rotating heatsink is thermally conductive and agitated by the rotation, so no static boundary layer.
Re:I'm curious... (Score:5, Informative)
I had the same question but it is very well addressed in the PDF:
During operation, these two flat surfaces are a separated by a thin (~0.03 mm) air gap, much like the bottom surface of an air hockey puck and the top surface of an air hockey table. This air gap is a hydrodynamic gas bearing, analogous to those used to support the read/write head of computer disk drive (but with many orders of magnitude looser mechanical tolerances).
Heat flows from the stationary aluminum base plate to the rotating heat-sink-impeller through this 0.03-mm-thick circular disk of air. As shown later in Figure 18, this air-filled thermal interface has very low thermal resistance and is in no way a limiting factor to device performance; its cross sectional area is large relative to its thickness, and because the air that occupies the gap region is violently sheared between the lower surface (stationary) and the upper surface (rotating at several thousand rpm). The convective mixing provided by this shearing effect provides a several-fold increase in thermal conductivity of the air in the gap region.
The PDF also goes into how this tech could have serious applications in things like home AC and refrigerator heat exchangers as well.
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There is 0.3mm of air between the base plate and the spinning impeller. Because this air gap is thin, wide and sheared (i.e, the top part is spinning and the bottom part isn't - so you get lots of convection), the thermal resistance of the air gap is actually very low.
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your work blocks PDFs from sandia.gov? but you can browse slashdot? or do they just restrict all PDFs?
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But I am curious how this alleviates that boundary layer...
Maybe it's a side-effect of using an air bearing? Little rotating concentrated jets of air blowing down on the hot metal plate....
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The heat transfers through the air bearing, which is very thin and in the paper is dry nitrogen gas, IIRC.
Re:I'm curious... (Score:4, Insightful)
Nope, the "connection" is a thin (1E-5m) air gap experiencing high shearing and thus providing very low thermal resistance. The gap's thermal resistance contributes very little (on the order of 10%) to the overall thermal resistance of the cooler. It is a truly revolutionary design, no shit here.
Re:I'm curious... (Score:5, Informative)
Yes, a layer of air does form between the heat spreader base, and the base of the rotating heatsink. This is called an air bearing. It's extremely thin, and for that reason an excellent thermal conductor even though it's conducting heat poorly. You see, it has a surface area of 100 cm squared, but it is less than 0.03 mm thick. So, heat transfer is inefficient, but its so thin as to be negligible.
And no boundary layer forms (well, it does but it is reduced by a factor of 10) on the fins because they are rotating. The equations for fluid dynamics are quite different between an inertial reference frame and a rotating one. Basically, the fluid cannot settle into little pockets because the (fictional) centripetal force is pushing it outwards along the fin channels.
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Basically, the fluid cannot settle into little pockets because the (fictional) centripetal force is pushing it outwards along the fin channels.
Oblig XKCD [xkcd.com]
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No, there doesn't need to be a stationary connection.
Here's the problem the boundary layer presents: The air in the boundary layer, by definition, has zero velocity relative to the solid surface, so the only way for heat to leave the surface is by conduction across the boundary layer. (Well, I'm ignoring radiation here, but I don't think that's very much.) The thermal conductivity of air is low, so it presents a substantial thermal resistance.
The effect of the Sandia device is not to eliminate the bounda
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Doesn't that mean that the impeller is actually a fan and not a heatsink? I mean, if it just sucks air over the aluminium plate on top of the CPU, doesn't that mean it's that layer of hot air that's blow away, rather than the heatsink actually getting hot and then blowing the air away?
I have some trouble grasping how even a really thin layer of air can conduct heat so efficiently from one solid object to another.
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No, the heat is conducted from the CPU to the baseplate, across the 0.03mm airgap, into the baseplate of the "fan", and up into the spiral fan "blades". The heat is actually transferred to the air from the sides of the "blades", ant the warmed air is flung out into the environment.
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A 1 micron air gap... Now not only can the heads on our harddrives crash, our heatsinks can crash, too.
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Oops, that's not a micron, it's only one one-thousandth. Still it's a whole lot more area in near-contact than a hard drive, and I might still worry about a heatsink crash. It might be safer to at least put a wire cage around this whole thing, so that at the very least some cable or wire doesn't come loose and brush against it.
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A head crash is significant because the magnetized substrate is damaged, frequently destroying the data which was stored on it. Here a minor scratch might occur resulting in a who gives a shit. Its two completely different events.
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also in the pdf they say that the air bearing effect on this is self regulating and allows for precision without the tight mechanical tolerances a hdd requires.
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The obvious solution would be to cause the spin to force air into the gap, so that the device is self lifting when operating. Use magnetic induction to do the spin and it pretty much can't fail. (Or at least, would be less prone to failure than existing designs, which should be all anyone cares about).
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in addition, page 10:
"As shown later in Figure 18, this air-filled thermal interface has very low thermal resistance and is in no way a limiting factor to device performance; its cross sectional area is large relative to its thickness, and because the air that occupies the gap region is violently sheared between the lower surface (stationary) and the upper surface (rotating at several thousand rpm). The convective mixing provided by this shearing effect provides a several-fold increase in thermal conductivi
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Apparently, someone forgot to tell chip makers about this "Brick Wall". Seriously, sounds like the author is making stuff up with absolutely no idea what he is talking about.
Contrary to your complete stupidity, the "chip makers", subscribe to his news letter. There are several significant issues with modern CPUs. One of the most prevalent issues is heat dissipation. Thus, accurately described as a "brick wall", as it is effectively preventing the creation of faster, general purpose CPUs.
Why does slashdot seem to attract so many completely fucking stupid morons who like to pretend they know something when in fact is obvious they known absolutely nothing anything anything. Holy shit you are really fucking stupid.
It's only to delay the inevitable: the move to liquid cooling. Chip manufacturers have made great strides in technologies to keep waste heat down and still get good performance, but one of these days R&D is going to turn out their pockets and admit they have no tricks left to get better performance on air alone.
It's a pretty scary thought, though, because liquid cooling brings all sorts of new issues that have never been before: coolant levels, biocides, toxicity, leaking, conductivity, contamination, m
Homeless (Score:4, Funny)
But think of all the homeless Dust puppies!!!
have you no shame?
Artificial intelligent heat exchanger? (Score:2)
That's exactly what the Air Bearing Heat Exchanger, developed by Jeff Koplow of the Sandia National Laboratories, has developed.
So I get it was not Jeff Koplow who developed it, but the Air Bearing Heat Exchanger did develop it. The Air Bearing Heat Exchanger in turn was developed by Jeff Koplow.
Oh, and BTW the link was missing a PDF warning.
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Historical prototype, prior art (Score:2)
Well this idea isn't new at all. Back in the 1910's aircraft engineers were trying to produce engines that could be cooled without heavy water jackets and radiator cooling systems. Putting cooling fins around the engine cylinders and block to let the passing air cool the engine worked, but not well enough given the state of metallurgy at the time. One solution was a rotating radial engine. In this configuration the crankshaft of the engine was bolted to the firewall and the block spun around with the cr
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A vegetable based oil was used (which had a laxative effect on the pilot!).
Or was it just coming up against the Red Barron?
One significant difference (Score:2)
In these "old" engines, the cooling block itself did not move, rather the engine it was attached to moved. The equivalent would be for an entire PC to spin in for radiators attacked to it to be cooled. This would be highly inconvenient for any cat owners as well as make it even harder to plugin that USB cable.
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The equivalent would be for an entire PC to spin in for radiators attacked to it to be cooled. This would be highly inconvenient for any cat owners as well as make it even harder to plugin that USB cable.
Standard socket and packaging technology is going to have issues with the centrifugal force and vibrations. Spinning the whole gadget and doing all the connections with sliprings for power (or solar cells and searchlights?) and bluetooth for I/O MIGHT actually work... Need to research bluetooth doppler sensitivity first...
Rotary engines (Score:2)
In th
Ferrofluidic seal (Score:2)
Check out Fig. 10 (Score:3)
I didnt RTFA but.... (Score:4, Insightful)
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Kinda depends on which PC manufacturers. Really, there are two diametrically opposed problems being solved: either you're going for the silent, no-moving-parts, low-cost, low-maintenance approach (commodity PCs, home-entertainment appliances, etc.)... or you're going for the balls-to-the-walls, maximum FPS, humongo display resolution enthusiast machines.
I definitely wouldn't group that first category all together. Silent/no-moving-parts really shouldn't be together with low-cost, and I'm not sure where low-
Is it such a new idea? (Score:2)
Don't some lawn mowers have heat sinks like this that spin atop the engine?
Anyway, I'm much more interested in the air conditioner applications of this than electronics use. I like the idea of a quieter, 30% more efficient air conditioner/heat pump. Great article.
No, it's the fan (Score:2)
does the opposite work as well? (Score:2)
wonder if the barrier is caused by the constant, unidirectional flow of air from a fan?
while it's hardly an efficient/practical design, would you achieve the same efficiency if you moved a fan around the heat sink?
A researcher at a US government’s lab (Score:2)
Tesla! (Score:2)
This is awesome. It appears to be using similar principles and design to Tesla's turbine! (From wikipedia, which doesn't have a good picture of the innards) "The Tesla turbine is a bladeless centripetal flow turbine patented by Nikola Tesla in 1913. It is referred to as a bladeless turbine because it uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine"
Re:Tesla! Not. (Score:2)
It appears to be using similar principles and design to Tesla's turbine!
No, that's quite different. This thing has blades. It's a centrifugal pump [britannica.com] for air.
RTFA (Score:5, Insightful)
I know its said a lot and should be common knowledge but I think it pays to stress it more strongly on occasion. This seems like an ideal time, READ THE FUCKING ARTICLE.
Several posts now, numerous mod points and dozens of follow ups all frankly making complete asses of themselves ironically complaining about how the IQ of /. has dropped while they make angry complaints and rants about the story that are fully addressed in the documentation.
and if you think that the fact that the summary screwed up is still a good sign of /. intelligence drop then you really need to look right back in the archives because bad summaries have been around on /. and virtually everywhere else pretty much from the beginning. Unsurprisingly the people posting the stories dont have total knowledge of the often fairly complex material posted and they screw it up good and proper on occasion. Which is probably why you should be judging the posts on the documents they link to and not the quickly thrown together summary by an admitted layman. Anything else is ironically a really stupid thing to do.
READ THE FUCKING ARTICLE.
(and no this doesnt mean the documentation is flawless but make commentary on that, not the summary, it will raise that intelligence level a lot of you are so eager to whine about.)
There is an exception for laptops (Score:3)
The exception to this rule is lap top computers, where available electrical power is extremely limited. In this special case, CPU clock speeds and fan rotor speeds are reduced to conserve power, albeit at the expense of CPU performance. At these low fan speeds the residence time of air in the heat exchanger is greatly extended, resulting in much higher exhaust air temperatures.
January 2010? (Score:3)
My first thought looking at the linked paper was, "January 2010? Why hasn't this been all over the place if the results are so promising?"
But there could be lots of reasons for that. Just sort of popped out.
Another question that comes up is overall system efficiency. One advantage of the current fan + heat sink paradigm is that in addition to moving air across the heat sink, which is not terribly efficient, the fan also serves to mix the heated air around the heat sink with the larger reservoir of surrounding air. They don't really directly discuss it, but my impression is that their design would result in very little large-scale mixing; one of the efficiency advantages is that they aren't moving large amounts of air around. It seems that in a setting like a CPU cooler this might be a non-issue, as you would still presumably be using case fans to move air through the case (exchanging the reservoir); but in something like an air conditioning unit, it seems like it would become limited by convection for larger scale heat transfer - or require an external fan for air exchange.
Basically, my concern is that while this method might be very efficient in moving heat from the base plate to the air in the immediate vicinity, you would then have the problem of heat building up around it. Perhaps not an issue where you have a small-scale device open to a large, room-temperature environment (or where you already have something in place to move air around, like a computer case), but it seems like it could be an issue moving to something like a residential air conditioner.
Still, it appears to eliminate the boundary layer problem, so you could use a pretty efficient, large, slow-moving fan for air exchange - so probably more efficient than blowing high-speed air across a heat sink, but something that would need to be considered in a full implementation.
Re:what?? (Score:5, Informative)
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Re:what?? (Score:5, Funny)
You sound angry. At thermodynamics.
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I think he just had an exothermic reaction.
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This is all explained in the article and PDF.
Don't come here and start mouthing off like you know what you're talking about when you clearly are too lazy to get past the summary and expect everyone else to do the work explaining it for you. You must be an MBA graduate.
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Re:what?? (Score:5, Informative)
I've read the paper and what you said is just silly, not insightful. The heat sink is separated from the base plate by a layer of air on the order of 1E-5m thick. This layer of air experiences large shear stress that keeps its thermal resistance low. It's basically an air bearing for the spinning heat sink. The stackup is thus:
1. CPU
2. Disk-shaped base plate
3. Air gap
4. Heat sink impeller
The major difference is that in normal coolers, fan has no heat dissipating function at al. There's no functional heat flow through the fan. In this design, the fan is the heatsink: heat does flow through it, and that's what makes it work so well.
From what I can tell, it's a truly revolutionary device. It has 5-10x lower thermal resistance than regular coolers, consumes ~5x less power than coolers of same capacity, and generates less acoustic noise to boot (it wasn't quantified, though). Ah, and also it doesn't get fouled by dust: ever notice how in usual CPU coolers the fan is usually clean or just sprinked with dust, when the heatsink is pretty much plugged with dust? In this device, the heatsink spins, so it stays clean, just like a fan would.
Whoever commercializes this for the HVAC market will be financially set, as in "playboy mansion" financially set :)
Re:what?? (Score:5, Funny)
it's a truly revolutionary device
haha! Excellent pun.
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Lazy AC that wants to be spoon fed information.
Go home and change your diaper.
Re:Transfer? (Score:5, Funny)
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While an entertaining post, one could speculate that building a spinning computer should not actually be that hard these days. You probably couldn't use spinning hard drives but SSD should work fine. Power could easily be supplied with some bushings. The hardest part would be video out, but I think there are high speed wireless video solutions. If not, you may be able to get away with bushings for this as well but your contact area has to be pretty consistent. The rest of the system could be wireless (
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I mostly agree but, I do have to point out... fans ARE pretty resistent to dust....in compairson to stationary parts near fans (like a traditional heat sink). While fan blades to accumulate dust, it happens much more slowly than the stationary parts near them.
A notable exception do seem to be ceiling fans, but they tend to be off much of the time and sit stationary and horizontal.
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Difference is that fans don't really need to be dust free to work, they still move air even when dusty.
This new concept might be vulnerable to the surface of the plate getting scratched up, or even fail catastrophically if something gets wedged into the gap. It will be interesting how it works out in practice, especially in uncontrolled air conditioning applications. Throw a handful of bugs and dirt on it, or rain, or even hail and see how it works compared to an current design.
Re:Still has a boundary layer. (Score:5, Insightful)
Re:Still has a boundary layer. (Score:5, Funny)
+1 sweetness factor, such a rare moment in /. land.
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*Man* you read and analysed those 44 pages of maths quickly.
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The article is bull feces.
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It still amazes me how many engineers on this site immediately dismiss the work of another engineer or scientist based on a summary by the media. I would have thought that smart people would realize that it is the regurgitators (I refuse to call them journalists) that don't know what they are talking about 90% of the time, not their fellow engineers.
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if you studied fluid dynamics in college, and stopped at the article before reading the PDF, your degree is bull feces. It's an extremetech article about actual technology, with physics involved in the explanation. what did you expect?
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Re:Still has a boundary layer. (Score:4, Interesting)
*Man* you read and analysed those 44 pages of maths quickly.
I skimmed them.
It seemed to very carefully avoid the issue of the bearing's heat conduction ability while explaining how spinning a heatsink does reduce its thermal resistance vs merely blowing air upon it. So you decrease the resistance at one end while ignoring the increase at the other. Hmm.
The other mystery is the straw dog of cheap and easy to machine heatsink designs (you've all seen them) have moderately bad boundary layer problems, so rather than a more elaborately modeled and machined heatsink design, or even more simply, a larger heatsink, the solution is a very complicated, hard to model, and hard to machine rotating heatsink. So, why not just put the hydrodynamic engineering hours and CNC machining hours into a GOOD passive sink that might work just as well? Or invest in a couple more dollars of aluminum, or skip it all and go for broke with waterblocks. Who knows?
Is there a middle ground for this design to live in between cheap and easy and inefficient non-moving sinks and much higher performance (and cost) waterblocks? I'm guessing, no. Not in any electronic system I've worked on (not just computers, but high power RF amps, high power audio, high power VFDs, etc)
The other problem is it makes for a more brittle design. Now you can usually shut down a system automatically when the cooling system stops, due to thermal mass, limited natural convection cooling, etc. With this, it'll be smaller and lighter, can you shut down in time to avoid frying the CPU (physically) or crashing the filesystem? Its going to make OTHER parts of the system design more complex, not just the cooling system.
Cool engineering (pun intended) but I'm unimpressed from an economic standpoint. It will probably cost more than the alternatives. Unless you're just trying to avoid a patent or whatever.
P4 thermal monitor (Score:2)
With this, it'll be smaller and lighter, can you shut down in time to avoid frying the CPU (physically)
I seem to remember Pentium 4 CPUs using a scheme like this: When the temperature exceeds one threshold, the "Thermal Monitor" puts the core to sleep for a few microseconds every microsecond. When it exceeds a higher threshold, the CPU halts.
or crashing the filesystem?
A reliable file system has to survive loss of mains power anyway.
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They do not avoid the bearings heat conduction ability:
As shown later in Figure 18, this air-filled
thermal interface has very low thermal resistance and is in no way a limiting factor to device
performance; its cross sectional area is large relative to its thickness, and because the air that
occupies the gap region is violently sheared between the lower surface (stationary) and the
upper surface (rotating at several thousand rpm). The convective mixing provided by this 11
shearing effect provides a several-fold increase in thermal conductivity of the air in the gap
region.
I see no reason why this should not be subject to cost engineering like any other component. Yes, they machined their prototype our of solid aluminium on a CNC machine. But they are not production engineers. It would seem to me that, as one-moving-part system, this should be subject to manufacturing optimisation over two or three years to be very competitive with equivalent air cooling systems.
Your point about the design being more brittle is relevant:
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If I understand what is being said:
In this set up we still have a fan of sorts, though if it stops rotating it doesn't afford the same advantage as a heat-sink + fan set up. It also means you need to have spinning device, no matter the heat level of the CPU, which means that you will still have a certain noise level.
I am not a fluid mechanics engineer, so bare with me as I as this question: If we kept the traditional heat sink, possibly changed its shape and instead got the fan to rotate around the outside
Re:Still has a boundary layer. (Score:4, Insightful)
It sounds like it's still in the research phase, which means it's not a viable commercial product yet. All the things you describe would need to be solved in order for it to be commercially viable. But the concept is novel, and deserves credit for what it is.
Whether this will ultimately end up being a replacement or a competitor in the current cooling systems market will be a matter of whether these problems can or need to ultimately be solved. Since this phase of the research deals only with the viability of the new design, I suspect it will be.
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Personally I think this is a neat concept and would like to see some how these pan out in the real world. While there's nothing wrong with being skeptical by any means there seems to be some merit behind this. I'm particularly curious to see how this would perform in an HVAC system.
Regarding your question about bearings conducting heat - I was wondering the same question. I wonder if there's a way to make bearings specifically for this application with heat transfer in mind while still providing decent perf
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Well - yes.
You can avoid dust in that manner.
But only if you wind up the fan speed to several tens of thousands of RPM, and make them sound like your case is about to explode.
And also - read the article - the heat is transferred by the conductive fan rotating over a thermal plate with a .001" clearance.
This actively massively stirred air has fairly low thermal resistance.
I note the pressure guage next to the device.
This is presumably connected to a large compressor, providing reasonable rates of high pressu
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This is presumably connected to a large compressor, providing reasonable rates of high pressure air, as you need for air bearings.
The average PC however doesn't actually have this.
Now you need to cool the big air compressor, which likely requires the whole air bearing arrangement. No problemo, you supply a little air compressor to cool the big air compressor. Now you need to cool the little air compressor, oh, its turtles all the way down, here.
The other problem is air bearings are real cool in a controlled system or for lab experiments, but in the real world fulla slugs of condensate water and compressor oil contamination, they're no walk in the park. As you've probably noticed t
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and the PDF accounts for that.
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You're wrong.
Basically, the layer of air between the thermal spreader (base plate) and the impeller if very thin and very turbulent, because it is 'grinded' between the the impeller and the base plate. That actually makes it a very good heat conductor.
It's explained very well in the Sandia Labs paper. Seems like a very plausible and good design.
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Look silly, proof is in the pudding. Off-the-shelf CPU coolers have about 0.8C/W thermal resistances, this thing has demonstrated 0.2C/W in version 1 prototype, and version 2 is estimated to lower it to 0.1C/W.
How well do bearings conduct heat?
An air bearing? Very fucking well. So much so that its thermal resistance is an order of magnitude lower than the thermal resistance of the heatsink-to-air!
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Look silly, proof is in the pudding. Off-the-shelf CPU coolers have about 0.8C/W thermal resistances, this thing has demonstrated 0.2C/W in version 1 prototype, and version 2 is estimated to lower it to 0.1C/W.
Almost, but not quite, as good as an off the shelf waterblock system now, maybe as good as an excellent waterblock system in the future, maybe, with some luck, in the lab.
Of if you want no moving parts, about as good as a poor heat pipe system, or ten to a hundred times worse than a truly excellent heat pipe system.
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Wow. Maybe Sandia should have just given you a call instead of all that research since you have all the answers.
No, turbulence mitigates the boundary layer problem, but does not remove it. This approach apparently, while not removing it completely, reduces it to the point where it's impact on the efficiency of the heat exchanger is negligible.
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I know this is /., but the lack of TFA reading comprehension for this article is crazy even for slashdot standards.
The PDF never claims that the spinning heat sink eliminates the boundary layer. They only claim that spinning the heat sink reduces the boundary layer thickness by several orders of magnitude. And it makes sense, as the speed of air over the impeller blades moving at several thousand RPM is quite a bit faster than the speed of air that can be pushed over a static heat sink by a traditional fan.
Re:Still has a boundary layer. (Score:5, Informative)
Good Lord. Have your psychiatrist adjust your dosage.
TL;DR version: Stationary heat spreader surface on top of the IC. Teensy tiny air gap, small enough to permit heat transfer while functioning as an air bearing between heat spreader and... the next part, a heat-absorbing rotary impeller which pulls heat through the air gap into its fins, which are in turn cooled by air flow caused by centrifugal acceleration of the air through the rotating impeller assembly (squirrel-cage-fan style).
I'm not gonna pretend that there's no boundary-layer effect over the impeller blade surfaces, but I expect it'll be less than the effect caused by the common "push air down into the cooler and have it decelerate and turn 90 degrees to exit" cooler. Flow-through coolers would be more efficient than that, but air still has to decelerate through the cooler, whereas this impeller cooler makes the air accelerate during the cooling action. That might make a difference.
How well do bearings conduct heat?
The generic answer is "depends on thickness of air bearing surface (i.e., how big of an air gap), coverage area of bearing surface (i.e., is the heat spreader the size of the entire impeller, or just the small central portion of it), and the rotational speed of the rotating part on the other side of the gap -- moderate rotation speeds, in the 2k to 10krpm range, make the air in the gap turbulent and sheared rather than laminar, forcing mixing and heat transfer.
WTF happened to /.
Well, in this case, an actual scientific research article of relatively high coolness and technical merit leaked past the editors. I understand how this could be upsetting to most slashbots, given the novelty and rarity of this type of thing. Certainly, t
Re:Still has a boundary layer. (Score:5, Informative)
(Emphasis added.)
How well do bearings conduct heat?
Again, the technical document makes it clear that the rotating heat sink is not coupled via a bearing to the surface it's cooling. Rather there is a very thin layer of air separating them. Naively one might think that this layer of air (generally a poor heat conductor) would become limiting, and there would be poor heat transfer from the hot plate to the rotating heat sink. However they address this:
So, basically by keeping the air gap very thin (30 microns), and by substantially shearing/mixing this thin air disk, its thermal conductivity can be sufficient to transfer heat up into the rotating fins. Overall a rather clever design.
WTF happened to /.
I agree a lot of junk gets posted to Slashdot. But in this case, a link was actually provided to a good technical document that answers many questions, provides schematics, and shows graphs of various performance measures.
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WTF happened to /.
It became popular, which widened the bell curve and probably lowered the average IQ (not by a lot, let's not flatter ourselves unnecessarily). We have a couple of capital-T Trolls here, APK and MichaelKristopeit, and it's always been unclear what the role of the editor is supposed to be since they don't appear to do shit. The GNAA contingent seems to have died down. Neither of us are submitting articles, it seems, and likely not participating in the firehose (there being no real incentive to do so).
Seems li
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IANAFD but it would seem intuitive that moving an object at velocity X through air is the same (from the object's POV) as moving air at the same velocity[1] over the stationary object.
Otherwise wind tunnels would be a total waste of time.
[1] In the opposite direction, so -X, to be pedantic.
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Except that when you rotate you are not only moving, you are accelerating.