Min. temp delta above room temp with water cooling

[rocketmanx]

Was just wondering out of curiosity if anyone has any idea, theoreticaly, what the lowest temp delta above room temp might be with straight water cooling.
We all hope to acheive as low a temp as possible with our water cooling setups but even with a "perfect" water block etc... exactly room temp will never be acheived. Or will it? Is it ever going to be possible, with nothing more than air cooling and heat transfer, via water, rad, air, to ever come within a couple of degrees of room temp?

Again, this is just out curiosity and I don't know the specific formuas for this, obviously, so I am asking here as i know there are several guys here that might know.

[Dieter@be]

damn that's more of a philosfy question
our cooling is getting better and better, but will face certain limits.
Only considering air and watercooling we might get pretty close to ambient temp.
But it 'll be more expensive then now, the closer you want to get the more $$ (or €€ in my case), until it would be stupid to give all that money to such cooling (instead of vapor phase for example)

[Cathar]

I believe that we are getting pretty close now.

For a 100mm^2 CPU die, and a strong pump, the best waterblock's C/W is around 0.14-0.15 (my guess - I could be totally wrong - and I know a number of people who would probably object to that figure - but anyway).

Of that 0.14-0.15:

~0.07-0.10 is due to the thermal paste layer
~0.020-0.025 is due to the thermal resistance of having the (thin) metal base-plate on the block (non-direct die)
~0.005 is due to the thermal capacitance of the water (the water does unavoidably warm up when in contact with the heat)

Which leaves an estimate of around 0.02-0.06 C/W being due to the block's design.

I don't believe that a figure of 0.02 is a realistic value. I'd say that the real figure is more like 0.04-0.06 C/W is what we have left to gain.

Mid you, that's for 100mm^2 heat sources. For larger sized heat sources the figure is lower.

For a 100W CPU, that represents a 4-6C gain still to be realised, and as little as a 3-4C gain for larger CPU dies.

I believe that there is the potential to eke out about another 0.01-0.02C/W (1-2C), but doing so will be quite difficult, but beyond that I don't foresee any gains being realistically made unless the thermal interface layer is improved dramatically (it too being at a near standstill for improvements of late).

It must be noted that these are just my personal thoughts on the matter from my understanding of what I've observed, not necessarily based in hard fact.

[rocketmanx]

Thanks for the reply Cathar

I agree since we're not that far off room now. I wasn't totally clear in my thought process but, I was thinking a little beyond the block and more toward what the actual physical limit of heat transfer really is with water and a given solid. As copper is more efficient than many other metals water has a given ability to absorb energy. I was just figuring what ever that was is as close to "theoretically" perfect a water system could be. I usually keep my wandering thoughts to myself but I wanted a little input on this one

And others may differ with you Cathar but who cares, I would assume those to be more the "engineering" type. I feel there's good engineers and good "constructors" or "implementers". You seem to be the version I respect most, a little of both, you know how to make it work and HOW it works

[Dieter@be]

You still respect me too, right?

[rocketmanx]

Yes
Didn't mean to make you feel leftout D

You're not an engineer are you ?
(I went for ME but only made a year before quitting to join the family biz)

[Dieter@be]

No I'm 18, don't have any tools, don't even have copper....yet
But I do have some nice (so I think ) ideas, I'm pretty much interested in the designing of waterblocks