CPU Cooling Challenge - Time For Water??

A case for watercooling – Joe

SUMMARY: Looks like the stars may be aligning for “mainstream” watercooling.

I’ve been observing the heatsink scene for going on five years now and every once in a while, I sit back and try to read the tea leaves to discern where things are heading.

The major event in CPU cooling has been CPU die-shrink (see “CPU Die Size – The Cooling Challenge Ahead”); basically the overarching issue confronting heatsink designers is how to cool more watts in an ever decreasing area. As the watts/mm² increase, wicking off heat becomes increasingly (maybe exponentially) more difficult.

An excellent paper by Kaveh Azar shows these trends very nicely:

Pwr Trends

Kaveh Azar, Ph.D. – paper HERE.

Note the sharp rise in power density starting 1999. The implication, as we overclockers know all too well, is that we are using alternative cooling technologies to deal with this trend, most notably water:

Power

Kaveh Azar, Ph.D. – paper HERE.

No question that aircooling is still the preferred method, considering cost and complexity; no question that how far aircooling can go is an open question (see “Heatsinks – Hitting a Wall??”). Looking at the physical properties of air vs water clealry shows these limits:

Limits

Kaveh Azar, Ph.D. – paper HERE.

If you’ve been around since ancient history (the last five years), you’ve no doubt seen heatsink increase in size. However, how far this can continue is also open to question (see “Heatsink Performance Limits”).

HS Size

Yogendra Joshi – paper HERE.

Note also from this graph by Yogendra Joshi, that as size increases, so does airflow; this translates to larger fans and, as we have seen, much more noise for aggressive performance. Many of us remember the stampede to Delta 38s, to be quickly followed by the stampede to throw them out due to intolerable noise.

One of the primary issues facing heatsink designers is spreading resistance – one technical paper found that “[When aluminum heatsink] length is changed from 50mm to 100mm, weight is changed from 133gm to 266 gm, completely double the weight, yet the performance gain is only 16%.” (Honglong Chen, paper HERE.) Doubling size by no means doubles performance.

Current materials (copper and aluminum) are about stretched to the limit of what they can efficiently handle. Until new aircooling technologies hit the market with cost efficiencies rivaling these materials, alternative CPU cooling technologies are likely to look more attractive; of these, IMHO water looks to be one of the better choices.¹

While watercooling is currently more expensive and complex, I believe the increased attention it appears to be getting from larger companies now entering the field may alter this markedly. Many “pioneer” watercooling manufacturers started as garage shop operations and some still retain these characteristics. As larger companies with more extensive financial and engineering resources enter the market, more effective solutions may see the light of day.

In addition, suppliers of key components, such as waterpumps and radiators, are beginning to take notice of this market and we can expect more products specifically geared for CPU cooling. Currently users and vendors are adapting products used for other purposes. For example, radiators designed for high pressure oil cooling may carry a cost penalty when used in very low pressure PC watercooling.

THERMOSYPHONS

One of the issues watercooling faces is the need for an active pump. One technology that is pumpless is the Thermosyphon. I tested one example, the “Calm-SV Liquid CPU Cooler”. Although performance of this particular example was not anything to get excited about, the technology is worth exploring.

The following diagram shows the basic principle:

Pic

Kaveh Azar, Ph.D. – paper HERE.

The attraction of a pumpless system is clear: waterpumps are relatively expensive and a clear “failure point” in a watercooling system. If it could be eliminated, costs drop markedly. One key point is that vaporizing the liquid is required by the CPU; this may require a liquid with a lower boiling point than water:

Props

Yogendra Joshi – paper HERE.

The design challenge then becomes selecting the right fluid for the application. Overall, an interesting technology that requires a fair amount of “art” to deliver superior cooling performance.

Conclusions

One thing about physics: It can’t be bent.

As CPU frequencies increase and size shrinks, escalating chip power densities will inevitably drive CPU cooling to more efficient solutions. Watercooling, once a geek toy, is breaking out to take a place in mainstream PC applications.

I always find it interesting that we overclockers deal with these issues a couple of years ahead of the “mass market” – in fact, we tend to pioneer these technologies. Kind of a nice place to be.

¹Apparently NEC agrees – see their watercooled PC HERE.

Additional Reading: The following sources delve into these issues in more detail:

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Discussion
  1. Exactly. How is dell going to ship their computers? Watercooling is too high of mantience for the average joe. Average joe wants a computer that runs and doesnt need mantience. How is dell going to ship their systems? Average Joe is afraid to open the computer up, and even more afraid to put water in it. I just dont see watercooling being in a dell unless someone comes up with something very inovative. Air cooling's days are indeed numbered though.
    I think fool proof would be a self contained unit within the case that does not need to be drained nor maintained. Also it would most likely contain a flow monitor in order to warn of a pump faliure.
    What means Fool Proof to you and I or in fact OEM's is simply not the issue, this is Joe Public who has been known to have problems using Windows.. I have seen tower systems placed on their sides and other stange angles that I would suspect watercooling systems would not be designed or like to run at.

    As suggested by the article the ever increasing processor tempratures will eventually require more advanced cooling systems than air... Im not sure that I would trust Joe Public with water sealed or otherwise.


    There is only as much time left for air cooling as there is untill the next process shrink. I don't think that current or futrue heatsinks have much more room for increasing power/area ratios that will be seen on the next generation chips. Maybe this generation will be able to get by, very warm mind you with heatsinks, but the generation after that or when they start trying to crank up speeds on 0.09, your goig to see more alternative cooling methods. Personally i think that the sealed "heat pipe" idea of convective liquid cooling will become mainstream during the next process jump, and after that actively ciruclated systems. I also believe that sealed units will probally be the thing that OEMs go after. Joe sixpack wouldn't like the idea of watering his computer.
    I have yet to read the article but I wanted to address this.

    Do you think any OEM will ship a nonsealed system? Its likely that the precautions used in an OEM WC setup may be just as complicated as the computer itself. This may be the only reason the OEMs havent shipped water cooled systems yet, they have yet to make it full proof. There have been stories of people receiving shipped OEM systems with the HS off...
    Exactly, "the maintenance issue"... most people can't take care of their current systems properly, think adding water to the equation's going to simplify things? :p
    One thing that concerns me, is what happens if Joe Public's system breaks down, are they going to drain the water before transporting the system to the repair shop ?... or splash it everywhere creating more problems... Will the mean that the system will be in the repair shop for a longer period of time as it will need to dry out before it can be worked on ?
    1, 2, and 3 answered

    Good topic -- we will have too difficult a time trying to convince most average PC users that cooling with water can be safe if done properly... but then you have the maintenance issue, and not to mention the liability/warranty issues from the OEMs (who will have to initiate such a radical move in the PC market).

    The answer's No, air cooling will not leave us... not until something equally "safe" (end-user perception here) comes about.

    I do think that, for enthusiasts, the days of air are coming to an end as overclocking requires a greater (than average) dissipation of heat than most air cooling can provide at a reasonable level of noise. End-users/newbs/Dell buyers won't care about a little noise even in future models, but I'm willing to bet that larger heatsink/fan combos will be going mainstream soon, and with slower fan speeds while creating more cooling capacity (Zalman's started this path for us). Quiet is important, people don't want a tornado next to them while they're surfing the net. Currently, most OEMs that run high-end processors are NOT loud, so there's still plenty of room for mhz in our current design, and we all know that over time things become more efficient... so it's a matter of moments until a more revolutionary cooling method, that doesn't require a leap of faith on the end user's part, comes around.
    1) I think that for the while air cooling is satifactory - for processors running stock speeds with non-extreme amounts of voltage running through them that is. What I do think will happen is an improvement in the cooling design, and a move away from the ultimate budget heatsink supplied with AMD chips for example.

    The Gainward card is intended for enthusiasts or just speed junkies only, as they obviously would not sell an uber-cooled card for the general public - that would mean that aside from the insane cost of the graphics card they would have to buy a watercooling kit too.

    2) I think that marketing gurus will probably be quite successful in marketing watercooling to the wider audience than the extreme OCer - people who want an extremely quiet cooling solution as said in a recent THG article on a kit would benefit.

    3) Putting all our PCs in Fridges? :p Anything is possible methinks.
    1. Time is limited for air cooling. But the reason air cooling is on the way out, is b/c the hardware makers seem to me more intrested in speed than quality. (i.e. PIII 1.13, Tbred-a, NV30)

    2. Socially we have been taught water and electronics are bad when mixed. In order for Joe six pack to believe that water is a good cooling component, there would have to be a mass marketing campaign by major companies endorcing water cooling and its "coolness". Simply placing a sticker on the front bezel saying "water inside" is going to scare more people than attract them. The move to water will have to be silent in that no one knows, or it will have to be a major event. I feel if you simply tell people "oh by the way your computer is water cooled inside", your going to end up freaking them out. I say this from experience, in that when people look at my water cooled rig they act like its giving of radiation and being close to it will turn them green.

    3. I feel air is the only solution and should be the only solution. I feel that the processor world is in a huge downward spiral. Both Intel and AMD are worried about who is going to be faster. They should be focussing more on making these chips run cooler than making them run faster. I am willing to bet if Intel stopped worring about making it to 4ghz, and tried to optimize their exsisting chips, it would be possible to passivly cool a 3ghz chip within two years. I really feel if the major OEMs (i.e. Dell, Compaq, gateway) were to say "look we have enough speed, just give us something we can make a quieter computer with", the industry would move in the right direction and there would never be a need more mainstream water cooling. Moving to water only gives the chip makers more of an excuse to rush products out the door. Products that under air cooling would be unstable.
    1. Yes. Watercooling is the next easiest (and affordable) way. However, many of the commercial efforts I've seen are pretty crappy. Commercial offerings will have to improve for watercooling to be a reasonable alternative to air cooling. There is certainly potential - custom setups have shown this. :)

    2. People have water cooled cars. What's wrong with watercooled comptuers.

    3. I think watercooling is the next cheapest cooling setup, at least compared to phase change systems.
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