Help understanding watercooling delta

[MagR]

Hi

I'm about to try a watercooling loop in my system. It is mainly to calm down the heat and noise of my sli GPU's but I will probably put my Sandy bridge CPU in the loop as well.

I've been researching the subject for a couple of weeks now and have one fundamental question remaining. When planning the cooling requirements (size of radiators, speed of fans) I've found various tables from Martin's and Skinee's labs to help. However the aim seems to be to get the water delta (water temp at radiator outlet minus ambient air temp) to 10 degrees centigrade.

I cannot find any explanation as to why 10 degrees should be used rather than any other figure (bit suspicious when we use decimal systems that this is arbitrary). I am assuming it is the point where components will be well cooled and any further reductions will need disproportionate increases in radiator size/fan speed (law of diminishing returns).

Can anyone shed any light on this? Is there any scientific backup to support the 10 degree delta?

Thanks in advance

Mag

[simontompkins]

I believe the term is a logarithmic scale (of cooling) . From what I've read there's nothing special about 10 degrees, just that as you say there's a diminishing return on trying to get the delta temperature past a certain point.

I also found this article that talks about this area which I hope you find useful
http://www.overclockers.com/guide-deltat-water-cooling/

[c.ruel]

This is a really difficult question to answer. I know because I have asked it on other forums and it is very hard to get straight answers from people!

My understanding is that within the watercooling community they wanted a metric to easily compare the efficiency of watercooling systems. So the reason people use delta T instead of component temperature is because it is readily comparable to other systems. For example if I had a simple cpu loop, which I took up Mount Everest, with an i7 in it massively overclocked so it put out 200w of heat into the water and I got a delta T of 10C then if I took the system to the Sahara desert and took out the i7 and put in a Phenom II that put out about 100watts then the Delta T should be 5C.

Just quoting cpu temperature or gpu temperature is not useful because of a number of reasons. The most important one however is as follows; the most inefficient part of a watercooling system is the block, the point of heat transfer (you are just going to have to accept that). It's also the point that complicates readily translating detla Ts into an actual cpu or gpu temperature you will get. Say you have a watercooling system with an i7 920 and two 480GTXs in sli (I deliberately picked hot components) and when the components are under load the delta T of the loop is 10C (that is the temperature of the water). Obviously you would expect the i7 to run cooler than the GTXs because it puts out less heat, but you would be wrong with this assumption because the block area at the graphics card will be more efficient at transferring that heat to the water than the cpu one. The reason for this I would assume is because the IHS on a gpu is larger and the components are more sparsely spreadout underneath it (although I could be wrong on that).

The reason watercoolers decided on 10C rather than say 7C (which I have heard some people bang on about) is probably arbitrary. However 10C will definitely give you better temperatures than on air. You could maybe even go up to 15 or 20 and on older components. You would still get better temperatures than on air with those delta Ts. However with newer components like 28nm cpus you might not.

As a last point some people argue that the advantage with watercooling isn't to do with the lower temperatures (these people have probably never tried to overclock an AMD chip!). They argue that it is to do with the fact you do not get sudden jumps in cpu temperature as water has a much higher specific heat capacity than air meaning if the cpu usage suddenly shoots to 100% and back down again to 20% on air the temperature will jump ... on water it shouldn't.

If you want more practical information on how much radiator or whatever you need for your system then reply with what case you have, components to cool, budget, max fan noise you will put up with and I can tell you how I would do it (I have only done one custom loop so I am no expert). Or someone like Gonz0 who does a lot of watercooling might be able to help you.

[Devastater6194]

I think it is just the point where anything else added will see diminishing returns.
Kinda like where the 560ti is best value for money while still being sufficient for games and anything above see's a worse FPS-£ ratio.