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CPU and GPU in parallel?  

post #1 of 211
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Hey all,

Still learning watercooling and just put in my first loop. However, I am already thirsty for more!

I am wanting to run my CPU and GPU in parallel and wanted to know if anyone knew if this could cause any problems? I invision this as simply having a "T" block or Q between the two on both the feeding and return lines. My hope is that this would lead to better temps and also a clean looking setup.

I am also looking into trying to use QDCs so that I can have the loop quickly unhook when I slide the motherboard tray out of the M8 and also quickly hook back up when doing any maintenance.
post #2 of 211
What percentage of the total water flow will go through each of the parallel legs? You don't know because it depends on how much restriction the CPU and GPU blocks have.

Also you get much less flow through each parallel part of the loop. That's an issue because there will be much less turbulence in each block and hence less heat transfer.

Watch out for QDCs, some are very restrictive.
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post #3 of 211
What he said.... lol

Most people use the loop in series... that allows for the lowest temps on the CPU which needs to be lower in temp to be stable to happen first, then the GPU which can run stable easier next. They also seem to be lower temps in custom loops easier for some reason (I don't know why, but it was in my first loop involving a GPU).

But.. also if your pump is strong enough it "may" provide enough flow to each component to work, especially if you do some research and figure out similar restrictions for each block involved. You may also need beefier pump. It could work, but requires syncronized restrictions to flow properly. If not, I imagine you find that one is hotter than the other because of an imbalanced flow rate, perhaps you can add a restriction to the second more free flowing piece. However this goes against most theory which involves removing as much restriction as possible allowing for lower temps.

"IF" both blocks provide a lower restriction than the radiator and the radiator is placed later in the loop, then the restriction of the radiator is going to be divided equally or unequally over the prior blocks. That's another reason why ultimate equality in restriction is necessary and is difficult to predict.
Edited by steadly2004 - 1/24/17 at 8:42pm
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post #4 of 211
Quote:
Originally Posted by steadly2004 View Post

"IF" both blocks provide a lower restriction than the radiator and the radiator is placed later in the loop, then the restriction of the radiator is going to be divided equally or unequally over the prior blocks. That's another reason why ultimate equality in restriction is necessary and is difficult to predict.
No. Any restriction the water "sees" is caused by what it is flowing through, not what is upstream, downstream, or parallel to that restriction. But the total restriction the water "sees" is the sum of all the restrictions it "sees" in the loop.

It's a different way of looking at it but that's the way your god made hydrodynamics work.
 
 
 
Edited by billbartuska - 1/24/17 at 9:26pm
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post #5 of 211
Quote:
Originally Posted by billbartuska View Post


Also you get much less flow through each parallel part of the loop. That's an issue because there will be much less turbulence in each block and hence less heat transfer.

Watch out for QDCs, some are very restrictive.

this is not right at all.

let me give you a simple example of the difference between a serial water loop and a parallel.

first thing I need to know when building a parallel water loop, is the flow rates of each component that will be on the water loop. I determine this by building a simple test loop with only a pump, a flow meter, and the component being tested.

for example lets say that the flow rates of these components are as follows.

CPU water block 4.0LPM
GPU water block 3.5LPM
radiator1 6.0LPM
radiator2 6.0LPM
reservoir 12.0LPM

with these components connected in a serial water loop the fastest the water loop can flow is 3.5LPM or the flow rate of the most restrictive component on the water loop.

with these components connected in parallel it is possible to achieve the high flow rate for each component in the water loop.
meaning that the flow rate on the CPU can be 4.0LPM, while at the same time the flow rate on the GPU is 3.5LPM, assuming that the total system flow rate is at 7.5LPM.

http://www.overclock.net/t/1573189/serial-vs-parallel-9-6lpm
http://www.overclock.net/t/1615072/cpu-and-radiator-upgrade-on-water-cooled-rig
http://www.overclock.net/t/1584867/tec-chill-box-chamber-build-log

I build all of my water loops about the same way, and they have flow rates from 9.0LPM to 12.0LPM.
post #6 of 211
Quote:
Originally Posted by billbartuska View Post

No. Any restriction the water "sees" is caused by what it is flowing through, not what is upstream, downstream, or parallel to that restriction. But the total restriction the water "sees" is the sum of all the restrictions it "sees" in the loop.

It's a different way of looking at it but that's the way your god made hydrodynamics work.
 
 
 
You are correct sir... I mis-spoke. I means if the downstream is more restrictive than the blocks..... The what's left will be unevenly distributed with less flow than without it. My bad. But I see what you're saying.

Sounds like you might me able to help me understand if I'm just wrong.
Hypothetically.....
If the radiator flows 4 "units", and one block flows 2 and another flows 3. Will the 2 not get a different flow than the 3?...Not speaking about the total flow? I understand the total flow will be restricted to the 4. Do liquids not flow to the path of least restriction? Wouldn't the block that flow 2 get less cool water than the clock that flows 3?


Basically if a flow is restricted to 4 "lanes" after the blocks and those 4 lanes are distributed over 5 prempting lanes. Then the 2 lanes will get 2/5 of the 4 lanes and the. 3 lanes will get 3/5 of the 4 lanes.
Edited by steadly2004 - 1/24/17 at 10:35pm
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post #7 of 211
Is there any compelling reason to go parallel vs series?

I'm thinking parallel would only help if your delta T is under 5 and you are worried about the CPU heating the GPU. Or if your flow rate is so high that the friction of the flowing water causes it to heat.
Edited by 0451 - 1/24/17 at 11:07pm
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post #8 of 211
Quote:
Originally Posted by 0451 View Post

Is there any compelling reason to go parallel vs series?

I'm thinking parallel would only help if your delta T is under 5 and you are worried about the CPU heating the GPU. Or if your flow rate is so high that the friction of the flowing water causes it to heat.

yea, it's possible to lower the load temperatures on the components by 8C or more with the same amount of radiator space. thumb.gif

http://www.overclock.net/t/1573189/serial-vs-parallel-9-6lpm

that's what I tried to show with this build. the difference between the load temperatures from the serial loop water loop and the parallel water loop with two pumps is 8C I did not add any radiators to the build or change the fans. all I did was change the configuration of the build, and increase the flow rate on the water loop by adding a second pump to support the hardware. biggrin.gif
Edited by toolmaker03 - 1/25/17 at 12:12am
post #9 of 211
Quote:
Originally Posted by toolmaker03 View Post

yea, it's possible to lower the load temperatures on the components by 8C or more with the same amount of radiator space. thumb.gif

http://www.overclock.net/t/1573189/serial-vs-parallel-9-6lpm

that's what I tried to show with this build. the difference between the load temperatures from the serial loop water loop and the parallel water loop with two pumps is 8C I did not add any radiators to the build or change the fans. all I did was change the configuration of the build, and increase the flow rate on the water loop by adding a second pump to support the hardware. biggrin.gif

Hmm I might benefit from this. I have 2 D5 pumps already. I might be asking you some questions after I buy more tubing.
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post #10 of 211
Quote:
Originally Posted by steadly2004 View Post

Quote:
Originally Posted by billbartuska View Post

No. Any restriction the water "sees" is caused by what it is flowing through, not what is upstream, downstream, or parallel to that restriction. But the total restriction the water "sees" is the sum of all the restrictions it "sees" in the loop.

It's a different way of looking at it but that's the way your god made hydrodynamics work.
 
 
 
You are correct sir... I mis-spoke. I means if the downstream is more restrictive than the blocks..... The what's left will be unevenly distributed with less flow than without it. My bad. But I see what you're saying.

Sounds like you might me able to help me understand if I'm just wrong.
Hypothetically.....
If the radiator flows 4 "units", and one block flows 2 and another flows 3. Will the 2 not get a different flow than the 3?...Not speaking about the total flow? I understand the total flow will be restricted to the 4. Do liquids not flow to the path of least restriction? Wouldn't the block that flow 2 get less cool water than the clock that flows 3?


Basically if a flow is restricted to 4 "lanes" after the blocks and those 4 lanes are distributed over 5 prempting lanes. Then the 2 lanes will get 2/5 of the 4 lanes and the. 3 lanes will get 3/5 of the 4 lanes.
Let's try this:

The race track effect

No matter what the flow rate is the water spends exactly the same amount on time in any component in a loop.

Consider a race track that is a one mile oval and has two lines painted on it 88 feet apart.
A car going 60 mph around the track spends one second between the lines each lap.
A car going 120 mph around the track spends one half second between the lines each lap.
But in two laps both cars spend the exact same amount of time between the lines because the second car gets there twice as often.

Sooooo:

Why does higher flow rates in a loop yield better cooling? There are two reasons:

1.) At the higher flow rate the temperature differences of the water between entering and leaving the block (or rad) are closer, so there's a greater Delta T between the block (or rad) and the water. This results in more heat transfer than if the water was moving slower.

2.) At higher flow rates there is more turbulence than at lower flow rates resulting in better heat transfer. (We could get into laminar flow vs non laminar flow, but that's not necessary here)

Soooooooooooooooo.

How does this effect serial vs parallel?

While there may be an overall flow rate increase with a parallel loop, at least one block (or rad) will have a lower flow rate, most likely they both will.

Perhaps these pictures will explain:





edit: Turbbulence is spelled wrong in the pic, but I'm to lazy to fix that.
 
 
 
Edited by billbartuska - 1/25/17 at 7:05am
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