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The Fanless Spinning Heatsink
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!"
You sound angry. At thermodynamics.
yes. the spinning heat sink is attached to a spinning cpu, which is in turn attached to a spinning motherboard mounted to a spinning case. these are only available in funhouses btw.
The stories and info posted here are artistic works of fiction and falsehood.
Only fools would take it as fact.
it's a truly revolutionary device
haha! Excellent pun.
SJW n. One who posts facts.
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.
ASCII stupid question, get a stupid ANSI
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
Welcome to the Panopticon. Used to be a prison, now it's your home.
(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.
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.)