Originally Posted by NaeKuh
Martin + Skinnee + Vapor + others i remember long ago HASHED this forumla out.
it translated to 300W per 1 gallon per minute flow in pure distilled h2o.
http://en.wikipedia.org/wiki/Heat_transfer_coefficient
From the above equation, the heat transfer coefficient is the proportional coefficient between the heat flux that is aheat flow per unit area, q/lund, and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, ΔT).
if im lost somewhere please teach me stephan.. your one of the guys i know who knows LC and thermo.
But watercooling in its basics is..
Heat is being released in blocks... water picks up... carries.. and then dumps.
That means when water picks up heat, it picks up energy and MUST increase in temp.
That number of Energy is in a relationship between flow and medium that is being used.. ie.. distilled water.
Water is non compressible, so were not going have crazy values which compressed gasses like LN2 would have as there is no evap involved.
Saying water WONT go up 1 degree after touching a X amount of heat is breaking the laws of physics.
So how much of a gradient is acceptable? or better yet do you even have a gradient?
If your a new user.. typically your gradiant wont be larger then 1C.
If you have 3 580gtx under load, with a full board block with a cpu block and a ram block, and you watercool your aquero controlller along with an ARC-1680ix... well... as i said, you need to pay for somethings.
yeah i wish people understood this..
the bridge on the nb -> Sb only allows so much without making it bulky.
Which is why the barb locations on most is made so you could connect a gpu to them without much trouble.
what exactly are you trying to show with this equation? "A" in your equation is the surface area on which you are calculating "h" - fluid properties have nothing to do with that. That doesn't explain where your "holding capacity of water" is coming from. This formula has nothing to do with the problem here.
When designing liquid cooling systems the only relevant equation would be: Q [W] = Flow [Lps] * Cp [J/Kg/K] * DT [K]
W is the amount of heat (in W)
Cp is the specific heat for Water (or Heat Capacity) and is equal to 4186 J/Kg/K.
Flow in Liter per second.
and DT is the difference in temperature between 2 points.
it only gives you the relation between the amount of Heat that is going through your liquid cooling system and the temperature delta between inlet and outlet.
you can use this formula to calculate the amount of heat that is going through any component of your loop: radiator, water block, etc (provided you precisely know your flow rate, and temperatures). Also note that formula is good way to decently approximate how much heat a CPU or GPU is putting into your LC system.
so if you take a CPU or GPU that puts out 200W - with a flow rate of 1 GPM (say 4LPM for easier calculations), your DT = 600 * 60 / (4 * 4186) = 2.15 C
Now say you run 4 of these: 3x GPU's and 1 CPU, that's 800W. Each of them increases the coolant temperature by 2.15C. let's keep things simple, say they're all in series, that's a total DT of 8.6 C.
Now we just gotta figure out what the coolant temperature is at the radiators outlet.
two MCR320-QP have a combined thermal resistance of 0.012 C/W at 4 LPM. For 800W heat load the coolant temperature will be 9.6C higher than ambient. If the ambient is 20 C, that's 29.6 C at the rad outlet (and at the radiators inlet you'll have 29.6 + 8.6 = 38.2 C).
See there is nothing here that remotely suggests a "limit" or even a sweet spot... If there is a limit, it is something you personally came up with based on your experience. But that is completely different than stating there is a limit and that is coming from the heat transfer formula you linked. And don't tell me water properties change with temperature because these variations exist but are irrelevant: Cp (I.E. water properties) is almost independent from temperature (4182 @ 20C ... to ... 4196 @ 80C) - so really water properties don't change - at least in the range that is usable by LC systems.
This was pretty much off topic... Anyways back on topic you disagree with the actual results shown in this thread - which is fine. But my problem is that you try to prove your point by stating there is a limit and that, basically single loop systems are going to be passed this limit and that is bad. Nope, there is no 300W limit with LC systems whether it's for computers, cars or anything. The only physical limit are coolant properties but here again they don't vary in any relevant way. In the 20 to 50C range of coolant temperatures (that probably covers 99% of the systems) it's all nice and linear: like you said xxx Watts = yyy C at zzz Lpm.
The only good point you make is bringing up the fact that Gabe's results prove single loops are the way to go for systems that take care of CPU and GPU when they are not all loaded at the same time. If we were to load up both CPU and GPUs all at the same time, then dual loops would probably end up each with a slightly higher flow rates, but not by much, which "could" result in slightly better temps but again not by much! Keep in mind that with the hardware to build 2 loops, you have at least 2 pumps and 2 radiators. There is no problem going in a CPU first then into a radiator, then into the GPUs and then into another radiator. This will smooth out the coolant temperature at the inlet of the blocks.
Also, unless you run 4 pumps, by going dual loops you will lose redundancy (as opposed to a single loop with 2 pumps in series). And anyway, who is loading CPU and GPUs at the same time? I am sure there are people who do that, I am one of them when I stressing our kits for pure testing purposes but is this the majority? I really don't think so.
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