CPU Cooling - How Much Better?

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SUMMARY: Is squeezing the last degree worth it?

I occasionally receive emails from readers who notice that good aircooled heatsinks are comparable to good watercooling kits relative to CPU performance (measured by C/Ws). The reaction usually run something like “Is that right?”

The answer is “Yes.”

A while back I wrote about Heatsinks – Hitting a Wall?? At that time, I thought breaking a C/W of 0.27 was the challenge (this on a 130 mm² die). With the CPU world now going IHS (die size about one inch square), it looks like a C/W of 0.10 (one inch square die size) is where CPU cooling is headed – here are three examples of cooling technologies and how well they perform:

Cooling Technology

Device

C/W

Watercooling

Swiftech H2O-Apex Watercooling Kit

0.08

Aircooled Heatpipe

Thermalright XP-90C

0.12

Thermosyphon

Prototype Tests

0.12

Can it get much better??

Physics limit how much further it can go – factors such as spreading resistance become more of a factor when trying to squeeze the last degree. With some more tweaking and optimizing, I don’t doubt that C/Ws in the 0.05 range are attainable.

What this translates to is 5ºC at full power at 100 watts over ambient temps. Currently you can get about 0.10 C/W with the best solutions – is 5ºC that much better?

Considering the way we use PCs, most people would be hard pressed to see any difference between 0.05 to 0.15 C/W. For extreme users, a 5ºC might be significant, but will it yield a performance difference at the CPU?

With critical CPU temps at about 65 – 75ºC, a CPU at something like 35ºC is going to be very happy. The key is getting ambient air at about 25ºC to whatever the heat exchanger is (fins or radiator); interior case temps can get pretty hot for a poorly vented case. Careful attention to case airflow can pay big dividends.

One technology that can drive temps lower is a peltier solution, but I would be hard pressed to believe that it would be adopted on a large scale – power consumption and controlling condensation are two factors that mitigate against it. And it comes back to “Why bother?”

CONCLUSIONS

There will always be a place for the $3 OEM heatsink that comes with retail packaged CPUs, as there will be a place for more exotic technologies, such as heatpipes, watercooling and thermosyphons. Each has its advantages / disadvantages, and end-users will have interesting choices in customizing cooling solutions to needs.

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