Review Index:

Cooling Capacity in a Multi-block Liquid Cooling Loop


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Typical Flow Diagram for Single Block Loop

All-in-one liquid coolers seem to be all the rage with several companies introducing expandable systems for integration of a system chipset or graphics cooling block to the loop. We will be exploring the performance of two of our previously reviewed coolers to see just how well those liquid coolers can handle the addition of an additional in-line graphics card block. Both the Koolance EXT-440CU Liquid Cooling System and the Cooler Master Glacer 240L Liquid CPU Cooler were used with the ASUS Poseidon GTX 780 graphics card placed in-line for testing.

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Typical Flow Diagram for Multi-Block Loop

Several key factors come into play in a liquid cooling loop that the addition of a second block effects including:

  • heat dissipation capacity of the radiator
  • flow rate of the system
  • resistance of the system components

Basically, additional liquid cooling blocks add more heat and longer tube runs to the system. This increases the amount of heat that the system must dissipate and introduces increased flow resistance to the system because of the increase of the loop size as well as the internal makeup of the added cooling blocks. The increase resistance and loop size directly effects the system flow rate and how hard the pump must work to keep the coolant flowing through the system.

For the purpose of this testing, we did not measure the liquid flow of the system directly. Rather, we measured the temperature of both components (the CPU and GPU) which directly correlates to the flow and heat dissipation capacity of the system. The ASUS Poseidon block adds little resistance to the system, besides the added length of the liquid channel, because of its simple U-loop channel internal to the block.

For additional information about the components used for this article, please see our review of the Koolance EXT-440CU Cooling System here, the Cooler Master Glacer 240L Liquid CPU Cooler here, and the ASUS Poseidon GTX 780 graphics card here.

Continue reading our analysis of Cooling capacity in a Multi-block Liquid Cooling loop!

May 14, 2014 | 11:05 AM - Posted by Anonymous (not verified)

I really don't agree with this diagrams flow direction.

Should be out of rad into res and out of res to CPU or GPU.... the end of the loop should be going to the rad out of rad to pump res out to CPU/GPU

May 14, 2014 | 11:47 AM - Posted by Morry Teitelman

You want to go directly from radiator to CPU block so that the CPU get the absolutely coolest possible coolant.  If you go from the pump or reservior, the coolant will absorb heat from the rest of the loop or from the pump before going to CPU...

May 14, 2014 | 03:37 PM - Posted by Anonymous (not verified)

That Theory is sound, but in practices it dose not really matter, because if you have a good pump, you have about 0.5c drop in temp from inlet to outlet of the rad.

And unless you want to be able to get the last one MHz out of your OC, i would not bother to much.

The main important things you need to pay attention to is a good rad and a good pump.

Also push fan setup is more effective then a pull setup for your rad.

I would avoid the EXT-440CU pump unit as the plague, unless you install a extra rad, as its a sub par solution, the CM pomp/CPU block is a o.k. start set, but noting more then that.

I just build in a Fractal Design R4 of a friends system, this set in:

1x EK-D5 PWM Motor 12V DC PWM Pump Motor - €70,95
1x Alphacool HF Screw connector G1/4 10mm - Deep Black - €47,60
2x Akasa 140mm Apache PWM fan Black - 1300RPM - €31,90
1x EK-Ekoolant CLEAR premix 1L - €7,10
Monsoon Silver Bullet Antimicrobial G1/4 Plug - €13,00
XSPC Acrylic Dual 5.25 bay Reservoir for D5 - €64,05
Alphacool NexXxoS UT60 Full Copper 280mm - €75,95
EK-Supremacy - Acetal + Copper - €60,95
EK-FC780 GTX Ti - €90,90
Totaal 465 euro

The pump is a PWM D5, so you dont need a special controller to adjust the speed, you can just connect it and control it with your motherboard fan controller software, PWM really rocks!!!!

A nice fat rad like the NeXxos UT60 cools a lot better then the rad's used in the article.

For comparison with a EXT-440CU and a Cooler Master Glacer 240L:

EXT-440CU - 120x210 rad 12 x 12 x 2.7 = 388cm3
240L - 120x240 rad 12 x 24 x 2.7 = 777cm3
UT60 - 140x280 rad 14 x 28 x 6 = 2352cm3

And till a certain point, size really maters with cooling!
The more rad you have the silencer your system is.

And yeah a custom build loop cost a lot more, but also works a lot better, and except for the GPU block, can be re-used on many new systems.

Quality over budget gives you better cooling, a more silent system and longer use of the parts, and above all it looks better to.

May 14, 2014 | 11:42 AM - Posted by Anonymous (not verified)

Block order does not matter in a watercooling loop. The only important thing is reservoir to pump, the rest can be in any order and it will not impact cooling performance.

May 14, 2014 | 03:26 PM - Posted by ZoranICS

You are very wrong there...

If the best overall performance is what matters (meaning you want the lowest possible temps on all of the components), then the block with the least flow resistance is the first after the pump and the block with the highest resistance is the last. Typically, the CPU block is the highest flow resistance - so that will be the last in the loop.

It does not really matter if the Rad is the first or the last in the loop. However, the pump is the most temperature sensitive component in the loop, so the rad should be the last component in the loop - to get the coolest possible coolant to the pump - as it will fail much sooner if the coolant is too hot. This is particularly true with systems tuned to low noise - as these systems see the highest coolant temps.

May 14, 2014 | 04:00 PM - Posted by Anonymous (not verified)

The only thing that matters is the prioritization of the components you want to cool. If you want more cooling capacity for your cpu, the cpu block goes first.

It doesn't matter which block has more or less flow resistance because the loop acts as a system. Liquid in = liquid out.

May 15, 2014 | 08:17 AM - Posted by ZoranICS

...believe me, I thought this was the case too. Then, one time, I had to turn the loop around and I found out is is not the case at all ;) Sure, temps on the CPU rose about 2C - quite logical, considering it now followed three GPUs, but overall temps were much lower. Test it for yourself if you need prof. You need to know which block has the highest flow resistance though, but like I said earlier - CPU Blocks are your usual suspect.

May 17, 2014 | 01:42 PM - Posted by Havor (not verified)

...believe me, if thats the case, then your pump is just to small!

I had with my old setup, Quad-CF 5870@950MHz and a 3930K@4.8GHz doing Furmark and OCCT.
I had a temperature drop of 0.7C over the inlet and outlet of my radiator, during normal gaming the drop was between 0.4c and 0.6c.

(From the 8 temp censors i have for my Aquaero 5 Pro, i picked two that ware the closes in temp with 0.1c difference between 20c/70F and 50c/125F, to measure the temp drop/delta)

I use a D5 pump, but the smaller DCC pump is for most setups more then enough, or any trustworthy pump that dose minimum of 400L/h (100gallon/h).

More flow means a more turbulent flow, means better cooling then a slow laminated flow.

May 18, 2014 | 08:42 PM - Posted by Anonymous (not verified)

This is just wrong. Thermodynamics dictates that it will get to a steady state, so , yeah, a non-issue which order the components are in.

May 14, 2014 | 12:38 PM - Posted by Anonymous (not verified)

Super cool to see PCPER guys!

May 14, 2014 | 03:07 PM - Posted by willmore (not verified)

Why don't you split the output of the Rad/Res and use a separate pump for each sub-loop? That way you can size the pump to the flow rate you need for the device it's meant to cool.

So, to be clear, put a Y on the output of the Rad/Res and run each output of the Y to a different device to be cooled. Then put a pump after that. Finally, combine the outputs of the two pumps with another Y which will then feed into the Rad/Res.

May 14, 2014 | 03:46 PM - Posted by Anonymous (not verified)

One thing I have learned over the years is that setting up the loop order is always hotly debated.

May 14, 2014 | 04:50 PM - Posted by Morry Teitelman

Keep in mind that the visuals shown display how the flow is setup in the All-in-One cooling systems used, and is not supposed to be a guide to optimal setup.  As has been stated, there are many differing opinions on loop setup, order, and flow control based on what type of cooling loops you build and how much experience you've had in the hobby.

Thanks all for the feedback though, its great...

May 14, 2014 | 09:50 PM - Posted by willmore (not verified)

Yeah, sorry, realized that after I posted.

May 15, 2014 | 11:52 AM - Posted by Justin150 (not verified)

Love the Poseidon card - definitely my next upgrade.

Also love the combined CPU block and pump but I do worry about long term effect of vibrations.

Personally I would swap the radiators for a 200x200 rad (bigger cooling surface large fan working more slowly = less noise).

What this shows is how easy it is to build a full WC in a real small space.

Water cooling is not for everyone, it is pricey for often minimal gains but it is fun and that is important

May 15, 2014 | 12:38 PM - Posted by BattMarn (not verified)

*reservoir, not reservior

(in the pictures)

May 15, 2014 | 08:50 PM - Posted by TheGlasman (not verified)

Glad to see some water cooling excitement again.
I'm going to throw hard earned water cooling bones into the pack just for fun.

Reservoirs are only a source of leaks (and reduce flow).

1/4" tubing systems are junk.

Overall performance is only improved by radiator surface area and fan cfm. (draw backs are size limitation problems and noise) Everything else does nothing because any 'improvement' is cancelled out by other factors.

May 16, 2014 | 01:49 PM - Posted by brisa117

Always great to see a liquid cooling story on PCPER! I think you would agree, Morry, that you're not a serious hardware enthusiast until you go with a proper cooling system -- even if it's just an AIO cooler! Love reading all your liquid cooling reviews! Also, they should have you on the podcast more. You're very thorough!

May 16, 2014 | 05:43 PM - Posted by Morry Teitelman

Thanks for the support.  I do agree that you really aren't hardcore until you go with water cooling, but I think its more of an enthusiast's evolution as they find that air cooling just won't cut it for the o/c and temps they want out of their CPU and GPUs.

At one point, I was doing phase change cooling, but got sick of the condensation issues that ensued - killed a few graphics cards from leaks in the condeser tube going to the CPU.  But my water loop is fixing to get upgraded in the very near future - multiple rads, pumps, and blocks on all my GPUs...

May 16, 2014 | 03:51 PM - Posted by FuzzDad (not verified)

The order of the loop isn't important to temps. Over time the entire loop will normalize to a set temp range based on the amount of heat your components generate and how much your water-cooling components dissipate heat. It's far more important to worry about your order in terms of connection points, tube length, the number of hard turns in your loop, fans, radiator sizes, aesthetics, etc.

There's a point-counterpoint argument for all the components you pumps = lots of noise but since you move more water through the rads you may get slightly better overall temps. Low speed high CFM fans might get you a nice quiet system but may not be able to handle cooling the water as well as you'd you get more fans or make them run faster...and that means more PSU power and noise...and so on.

The key is finding the right balance to meet your personal needs. I like a quiet system and will sacrifice on the temp side.

June 5, 2014 | 11:45 AM - Posted by Lord Binky (not verified)

Whether it's the air through the radiator or the water being pumped through, the real output of your fan/pump is dependent on the total resistance it's pushing against. If you want that high airflow/coolant flow you better have the pressure to back it up against the resistance you have in it.

May 20, 2014 | 06:13 PM - Posted by ButtonPuncher (not verified)

As others have said... I don't understand why people don't split the output of the radiator and have one feed for the CPU and one for the GPU. That will give you the lowest flow restriction and the GPU's coolant won't be pre-heated.

I like to mention too.. If you've got the space, build a plenum between the fan's output and the radiator. I like to take junk fans, cut everything out except for the body, and use it as a a plenum. Stack two if I've got the space. You kill an axial fan's flow when you slap it right on to a radiator. A sirocco (squirrel cage) fan, it doesn't matter.

May 23, 2014 | 10:59 AM - Posted by zinixo1 (not verified)

1:A faster/stronger pump is not always the answer,it really depends on what you are cooling [1 or more devices].A super fast pump can actually raise temps due to the friction of the pump.
My old system had cpu,chipset,mosfet and 2 gpus on one loop.My pump always ran on low for silence,if i cranked the pump up to screaming lvs the overall temp would remain relatively the same [maybe 1-2 c difference under a full load]

2:Every case /system is different .What works well for one wont necessarily work well for another.
3: block order can be anyway thats convenient for your build.
4: a few degrees higher or lower will make little if any difference on system performance.

May 24, 2014 | 12:40 PM - Posted by TheGlasman (not verified)

As others have said... I don't understand why people don't split the output of the radiator and have one feed for the CPU and one for the GPU. That will give you the lowest flow restriction and the GPU's coolant won't be pre-heated.

Splitting the pump out put reduces flow to both blocks, with most of the flow going to the gpu (lower restriction block).
Turbulence within the block improves heat transfer and low flow reduces that factor.

At any rate water temps are raised about 1C through the whole loop, so temp rise between blocks is not really a factor.

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