It is currently Tue Sep 16, 2014 6:51 am

All times are UTC - 8 hours




Post new topic Reply to topic  [ 35 posts ]  Go to page Previous  1, 2
Author Message
 Post subject: Re: Spinning heatsink
PostPosted: Thu Jul 21, 2011 5:30 pm 
Offline

Joined: Tue Jul 19, 2011 5:42 pm
Posts: 3
Mike,

I apologize if you thought my last post was unfair. It’s just that it’s clear from your five salient points that you hadn’t read the material, but nonetheless felt inclined to be broadly dismissive. Your skepticism is understandable in light of what you said regarding the long string of disappointing product introductions over the past 10 years. But my opinion is that posting comments such as “0.2 C/W is no big deal” without understanding the technical context is at a minimum counterproductive. The significance of the 0.2 C/W result is that if you divide through by the surface area of our heat exchanger, we are transporting 30 times more heat per unit surface area than a conventional fan-plus-finned-heat sink arrangement. Apparently something very interesting is going on here. The implication is that if we make the heat-sink-impeller larger, with more fins, we can bring the thermal resistance MUCH lower. Saying “0.2 C/W is no big deal” is missing the entire point. In my opinion, an editor has a responsibility to make sure that he/she is fully informed before passing judgment. This is because the vast majority of people reading your post are likely to assume that everything you say is accurate and complete. If I were an editor this would be one of my greatest concerns.

With regard to the objective of CPU cooler improvement and optimization, it may be that for the most part we are talking cross purposes. For the most part, we are targeting demanding applications that can’t be addressed with today’s air cooling technology. The ability to overclock an entire server farm, for example, strikes many people as a compelling value proposition; from the comments in your 2nd post, I surmise we’re in agreement on that. Check out http://www.tomshardware.com/reviews/rad ... 97-18.html to see the power draw (idle and max), and noise levels for several contemporary Nvidia graphics cards. There are many people concerned with reducing fan noise who operate at very high power levels. Again, based on what you wrote in your last e-mail, we concur on this point as well. If the maximum amount of heat you will ever be called upon to remove is of order 5 W, then I would be the first to agree that that you will have no problem achieving what most people consider very low noise levels.

I would also agree that without quantitative acoustic data it’s hard to know just how good a given device will turn out to be in practice from the standpoint of noise (or perceived noise). On the other hand, the fact that none of the waterfall-like white noise one would expect is present when operating this device at 5000 rpm is suggestive that there is something different about this device topology from the standpoint of noise generation (and worth mentioning rather than not mentioning). I think that was part of the reason some of your readers found air bearing heat exchanger interesting. Basically what it boils down to is that unlike a conventional fan, we have a great deal of design flexibility with regard to the shape of the heat-sink-impeller blades. Thus we are free to design the fin geometry around the goal of cleanly parting, and then cleanly rejoining, the flow field at the intake and exit of the impeller channels. This decoupling of design constraints is very valuable from the standpoint of reducing noise. Having said that, if your heat sinking requirements are limited to 5 W, extremely low noise performance is readily at hand using conventional technology.

I also agree that C/W is a highly imperfect proxy for actual performance on different platforms. We are in the process of setting up a test bed for A/B comparison heat sink testing on two identical Core i7 CPUs. In addition, we are setting up a “synthetic temperature test platform” such as those used by FrostyTech for precision measurements. The data collected on such test beds (e.g. 23.2 C temperature rise at 150 W power dissipation) is widely used for inter-comparison of CPU cooler performance, and is well correlated enough with real-world performance to considered valuable.

Lastly, I appreciate your offer to assist with measurements. My understanding is that Sandia has an alternating wedge anechoic chamber down at our New Mexico facility which we can get access to during periods of time that they’re not conducting measurements for other projects. Having said that, I would be the first to agree that when a technology is mature enough to productize (ours is certainly not), it’s time to have measurements of cooling performance and noise conducted by a disinterested third party who has established widespread credibility in the community.

In summary, I think we have cleared the air. I suspect our utilitarian outlook with respect to acoustic performance (if it’s unnoticeable, it’s not of great concern) is somewhat incongruous with your priorities. If you think I’m holding you to unreasonably high standards as an editor with regard to the five salient points from your first post, maybe you’re right. At any rate, to the extent that I conveyed it in an insulting way, I apologize. I have a lot of respect for the “old hands” in areas such as this because real-world experience and know how is critically important to doing work that is well informed, credible, and reported in terms of meaningful objective metrics. One the other hand, there is sometimes a tendency to fixate on certain ways of looking at things, and when that happens, technology improvements are often agonizingly incremental over extended periods of time. What many people found interesting about the work conducted at Sandia is that we attacked the noise problem from a completely new (and highly plausible) angle, much as we did the thermal boundary layer problem, and the dust fouling problem, and that it all three goals are being approached in a manner that is mutually compatible. Air bearing heat exchanger technology will succeed or fail on the basis of its merits in real-world applications. For now, I would advocate withholding judgment in favor of exploring the potential merits of what our research team came up with by starting with a clean sheet of paper.

-Jeff


Top
 Profile  
 
 Post subject: Re: Spinning heatsink
PostPosted: Fri Jul 22, 2011 9:47 am 
Offline
Site Admin

Joined: Sun Aug 11, 2002 3:26 pm
Posts: 11846
Location: Vancouver, BC, Canada
jkoplow -- I admit my orig post was made in haste w/o a complete read, and likely too dismissive. But the lack of substantive info on noise and mention of many thousands of rpm were not promising. Anyway, we understand each other better now.

5W is not what I suggest heatsinks in silent PCs are cooling, but rather, that <10W is the average CPU power profile for most users over the long term. Most silent PC enthusiasts opt for overkill in the heatsink for the few minutes when the CPU will be red-lined from time to time, and combine it with extremely slow fans (typically <1000rpm, often as slow as 500rpm) that have a "benign" acoustic signature. Some prefer the safety of fan speed controlled automatically by CPU temp while others like to keep the fan speed fixed so there is no variability in noise. For the latter, even if the CU heat at load exceeds the HSF's ability to dissipate, because of the HS's size & mass, it will still take some time for CPU temperature to reach throttling (there is virtually no risk of burning the CPU these days, as you know) -- and the typical application will not apply that kind of sustained high load long enough for the temp to reach that high. So the heatsink is usually a large heatpipe tower, and the preferred fan size is 120mm. Good ones start as low as $30, btw -- Coolermaster Hyper 212 comes to mind.

Interesting that you say there is no turbulence noise in your device... but you should realize that when a fan is slowed to <1000rpm, it is the least important aspect of the overall noise profile, as the level of that noise drops to the limit of audibility. Instead, tonality and variability in the noise take on far greater importance. Like I said, send us one to check in our lab. We'd be interested in just the acoustic behavior alone. I think someone else brought up this idea: In a conventional HS, users can generally swap out different fans and try them at various speeds to find one that suits their purpose and hearing sensibility. But if the noise profile of your device is offensive to them, there's very little that can be done -- other than reducing rpm, which might or might not solve the problem.

It is in small PCs that silent and fast performance is harder to achieve -- for the simple reason that there isn't enough space for the big overkill heatsink. Again this is where your device could be really useful -- as you know, PCs (not just mobiles) are getting smaller all the time. I would venture to guess, however, that vents to exhaust hot air and to allow outside air intake would still be essential in a small case -- and this probably means you cannot forgo a case fan. It is extremely difficult to rely on convection alone to dissipate heat from a small PC case.

_________________
Mike Chin,
Editor/Publisher, SPCR
Support SPCR with your donations!


Top
 Profile  
 
 Post subject: Re: Spinning heatsink
PostPosted: Sat Jul 23, 2011 9:59 am 
Offline

Joined: Thu Feb 04, 2010 6:06 pm
Posts: 3395
Location: US
I have been thinking about this. I believe there is a small but strong market for low height after market CPU coolers that is growing and will continue to grow. It would be an ideal initial application for this technology provided that it is quiet and performs well in the reviews.

It is ideal as the aftermarket will pay a premium and can be served by a small run product that will not require massive production runs.

_________________
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
"Aristotle calls man the rational animal. All my life I have been seeking evidence to confirm this" Bertrand Russell
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former" Albert Einstein


Top
 Profile  
 
 Post subject: Re: Spinning heatsink
PostPosted: Sun Jul 24, 2011 7:27 pm 
Offline

Joined: Mon Apr 25, 2005 10:00 am
Posts: 2131
Location: Grand Rapids, MI
CA_Steve wrote:
+1 to Mike's post.

Seems odd that a principal investigator at Sandia opts to be rude in a public forum. Then again, a username here doesn't provide provenance. The poster could just be "some dude". If he is the researcher, then perhaps he should look through this site and keep reading until he realizes our baseline is "inaudible" in a quiet environment.

Agreed.

The proof, they say, is in the pudding. If this technology works, it will be proven out over its development phase.

However, I didn't think MikeC's reply was irresponsible at all. He's run this forum for a LONG time and knows his users well. He simply voiced the same concerns many of us here would. We've seen all to many "newfangled" cooling methods come and go with very few actually sticking around for the long haul (I'm looking at you, Heatpipe). When you have simple and low cost solutions that are already entrenched, you need to offer a significant upgrade in performance or cost to make it attractive (at least in the standardized, commodity PC community).

As other have said, this seems more suited for the small form factor IT (blade server) market where systems would be kept running at higher loads more consistently.

_________________
HTPC: OrigenAE X11|Gigabyte GA-MA785GPMT-UD2H|Phenom II x3 740BE w/AC Freezer 7|150GB Velociraptor|Corsair VX450
Main: Antec 300 (SlipStream @ 800rpm/140mm @ 5v)|Asus M4A88TD-M|Phenom II x4 945 (Mugen2 pass.)|Asus EAH6850|Samsung 830 128GB|Antec TP750
WHS: DF-85|P8H67-M Pro|I5-3450S/Hyper 212+|Corsair AX650|Sandisk Extreme 240GB, 2xWD20EARS, 2x WD15EARS, WD15EADS


Top
 Profile  
 
 Post subject: Re: Spinning heatsink
PostPosted: Sun Jul 24, 2011 7:47 pm 
Offline

Joined: Thu Feb 04, 2010 6:06 pm
Posts: 3395
Location: US
jhhoffma wrote:
When you have simple and low cost solutions that are already entrenched, you need to offer a significant upgrade in performance or cost to make it attractive
The traditional rule of thumb is to have both, though perhaps that is a bit simplistic.

_________________
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
"Aristotle calls man the rational animal. All my life I have been seeking evidence to confirm this" Bertrand Russell
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former" Albert Einstein


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 35 posts ]  Go to page Previous  1, 2

All times are UTC - 8 hours


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group