Best liquid for CPU water cooling

[Wuden]

Just a hypothetical
What would the best liquid be for removing heat from a CPU and releasing in a radiator.

i assume thermal conductivity and heat retention would be important.

My knowledge in this area is near zildge.

water better then rubbing alcohol?
Mercury best conductivity?

Alcohol ?

Surface tension an issue?

Thanks in advance for your insights

Christian

 

[reidh]

If all you are looking for is thermal conductivity, then yes, water is better than alcohol by a factor of 3. And mercury is about 15 times better than water.

However, there are obvious issues with these liquids, which is why this isn't a straightforward problem. With water comes corrosion. That is one of the reason car's have antifreeze. Mercury is obviously poisonous etc. etc.

Viscosity also plays an important role when designing a cooling system. Maybe I should have asked this question first: Do you already have a pump, radiator, etc. specified, and you are just trying to find the right fluid? Or is this a ground-up design?

Then we can help you a little more.

Reidh

 

[kenvlach]

If 1) Relying solely on heat conduction, and
2) not using a pump, solid silver may be better.

The most efficient means (w/o pumping) is a heat pipe. For CPU cooling, neither water nor mercury is suitable. The working fluid should boil at a temperature that of the operating CPU temperature but above the cooling air temperature). So, the temperature determines the suitable fluids (& don't forget mixtures).

Since the heat pipe should be gravity-independent (not fail when the CPU is above the radiator), include a wick to return condensed fluid to the CPU.

And if one knows zildge (zilch?), begin here:

http://en.wikipedia.org/wiki/CPU_cooling#Spot_Cooling

 

[pipehead]

Freon, see CRAY computers

 

[IRstuff]

Boiling the coolant is usually bad, because boiling reduces the overall heat transfer at the interface, since it prevents fresh coolant from reaching the hot plate.

There are, of course, tons of heat pipe CPU coolers on the market, so rolling your own is probably only an academic exercise, although might be an interesting one:

http://www.subzeropcs.com/akasa_evo_120_cpu_cooler.html

http://www.bigbruin.com/2006/ultra120_1

http://www.silentpcreview.com/article114-page1.html

The Cray actually used Fluorinert:

http://en.wikipedia.org/wiki/Fluorinert

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