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Radiator and loop sequence question

post #1 of 5
Thread Starter 
Hi guys

I'm planing on building my second WC loop. My first loop was quite simple with only cooling my CPU. Now I'm working on building a WC loop that has to cool a CPU and 2 GPU (460 GTX). My primary goal for this loop is to getting my noise level down and second - lowering my temps. As it is now, the noise level is almost insufferable, and my temps is running quite high.

I have read various guides and articles to prepare myself and from what I can tell cooling a CPU and 2 GPU requires a 120.3 radiator to get good cooling. The problem is that though cases I am looking at right now only have space for a 120.2 radiator (some have the option of 140.2). So the first question is:

Can I run a 3 unit cooling setup on a loop with a 120.2/140.2 radiator and still get decent cooling out of it? Remember, I'm looking for lesser noise, then temperature reduction.

Then there is the loop question. Since I have 3 units I need to cool, I figured that running everything in series might be a bad idea. The last unit in the loop will always run higher than the rest. So I'm thinking of doing some kind of split. 2 options comes to mind:
Option 1:
                      |                   |
                      --> GPU1 --> GPU2 ---
Option 2:                                 
--->Pump--->Radiator----> CPU ------>Res--->
                      |          |         
                      --> GPU1 --- 
                      |          |
                      --> GPU2 ---

Option 1: Divide the CPU and GPU's. Here one of the GPU might suffer due to the GPU's are in series
Option 2: Divide all the units. No units will suffer, but I might get a problem with the flowrate, since the flow is split into 3 paths. I could get larger tubing for the serial part of the system and then smaller tubing for the parallel part, but then the build gets more advanced than I really wanted.

So which option for you guys think is the best?

I'm trying to get as much experienced inputs as I can. I believe you guys know more about this than I do, and research can only get you so far. Experience is way more important.

Thank you in advance.
post #2 of 5
Both option1 and 2 will result in loops with limited control. CPU and GPU blocks resistance isn't linear with flow rate of eachother. For instance with option1 if your cpu block is the same restriction as a gpu block at 2gpm, it would receive twice the amount of water as the gpu blocks. But let's say at 1gpm the cpu block is only half the restriction of a gpu block, it would get four times the amount of water and you can start getting in trouble with the gpu's. This example isn't realistic btw but it's to show that bad things could happen.
A more realistic example is option2 where gpu blocks have only half the restriction of a cpu block. It would mean your cpu would end up starving for water.

The only way option1 or 2 would be viable options, is if you would do extensive research on the restriction+flow rates of the blocks and calculate the gpm needed to get the water flow that you plan to get. And you could get control over the loop if you add 2valves in option1 or 3valves in option2 to regulate water flow to the parallel lines.

If you want that control and add valves, your options will work. A lot crazier flow constructions have been made with a lot of valves to regulate everything.
Otherwise go for
--->Pump--->Radiator---->CPU-----> ---GPU1 ---->Res--->
                                 |          |
                                  --> GPU2 --
--->Pump--->Radiator----> CPU ---> GPU1 -----> GPU2----->Res--->
post #3 of 5
Thread Starter 
Ohh, I didn't consider that. Thank you for that input. That could have been ugly.

Well, I'm not going to do valves and what not so it's going to be the options to put on the table. Might go with the first one.
post #4 of 5
--->Pump--->Radiator----> CPU ---> GPU1 -----> GPU2----->Res--->

This is your best bet. As little restriction as possible. If you want to run split/parallel blocks, you might as well just get a second pump and make a smaller second loop. This is how I personally do it. The reason for it is pretty simple, if it is all linear and has no 90 degree angles, or tight restrictions, thermal dynamics will take care of the rest. The water will flow quickly and maintain usually a +/- ~1 degree Celsius difference.

However, with 3 blocks you may want to consider the power of your pump(pressure) and how much is being lost at each block. use this spreadsheet to find your approximate values and see where you are;


I love Martin's Liquid Lab, he has a *lot* of great information up there which will really help. Good luck!
post #5 of 5
I don't see a single 120.2 or 140.2 radiator being enough for a CPU and two GPUs. You said you need a 120.3 for good cooling, but the truth is that a 120.3 would be the bare minimum and require that your fans run pretty hard when all three are at full load. It also matters exactly which CPU and GPUs you are talking about because you need to add the three TDPs along with an extra 20 for the pump to find out how many watts you need to dissipate. You can find some data on the watt dissipation of different radiators from SkinneeLabs and MartinsLL at different fan RPM speeds.


You may be better off sticking with air cooling if you don't have any room for radiators. Consider the total fin surface area of the heat sinks you would have using air compared to what you'd have using water. The whole purpose of water cooling is to be able to move the heat around and provide a greater surface area for cooling than you would be able to get with air, plus the added benefit of having the cooling air come from outside the case. I don't see water being a benefit to you if you need to cool all three components with only a single 120/140.2 radiator: you'd be reducing your fin surface area by quite a bit compared to even the stock air coolers.

I'd say keep the CPU on the 120.2 and keep the video cards on air unless you can find room for more radiator.
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