Pump pulling from CPU does it make a difference?

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Originally Posted by Erasmus354

No flow rate is not the only thing that matters when choosing a pump. Head pressure is still very important. If you look at pump PQ charts you will notice it is a curve. The pump produces different flow rates at different pressure differentials. In general pumps with higher maximum head pressure will get more flow in a water cooling loop when you factor in the pressure differential.

If you were to graph the pressure vs. flow of all your watercooling components combined and superimpose that on the pump pressure vs. flow chart where the two lines intersect is the flow rate you will get in your loop. The Watercooling estimator spreadsheets show this relationship very well. So you want to chose the pump that has the best flow rate for your components (intersects the pressure vs. flow curve of your components at the highest flow rate).


As for temperature drop from a radiator. A 400Watt loop with 4lpm flow (~1gpm) will have a temperature drop of 1.43 degrees celsius from input to output. And you are correct in pointing out how little heat the pump dumps into the water. In that same loop the 20W heat dump pump would up the water temperature by only ~0.07 C. If you assume 200W cpu and 180W gpu and 20W pump if you were to put the radiator directly AFTER the cpu you are losing ~0.7C in water temperature as opposed to putting the radiator directly before the CPU.



@Martin: Great explanation, you put it much more succinctly than I ever could have.

@Naekuh: o.O never thought I would see the day.

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OK, now I get it (hei, didn't I say that before? :rofl::rofl::rofl: ). Still, the only thing you want is the best flow rate possible...and to get that you need to know how restrictive is your loop in order to know how pressure differencial will affect the flow rate in your loop because, as you said (and that was the thing that I was missing since the beginning), flow rate, althought constant throughout the hole loop, varies depending on your loop (elbows, blocks, etc) and this is where pressure head matters.

Thanks again, you should consider at all to put some of this to some of the stickies because although there is most of it, there are some missing points that are asked once and again and again yet there is no place to be referred to in order to know them. But hey, it's nice to know that you could ask it knowing that no matter how many zillions time it has been posted before, you will get a reasonable answer :D

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Originally Posted by nikhsub1

To be clear, I never mentioned once performance vs pressure in the loop, I was just hoping for people to get a grasp of how pressure drop works in the loop, my intent was not to prove or disprove anything regarding performance. Now I think I will though Highly restrictive blocks may benefit from being right after the pump, they will receive the most pressure and will get the highest velocity possible with this placement. Of course, how much better (or possibly worse) would it be than say being after the RAD? Probably too small a difference to matter.

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If anything that has been written is correct (which I believe unless proven wrong) is that the only thing in which the order of the loop matters is when:
a) You make the loop shorter (without putting elbows nor other stuff that may add restriction) so there is less pressure drop and thus you get more flow rate (so, more performance)
b) You put the rad after the pump...but here the only difference will be that the pumps heat will be transferred before it gets into the loop...but thats something negligible because it's just a few watts, don't think It's going to make any difference.

If you've got a certain loop, the only way to improve it's cooling capabilities are:
a) Reducing pressure drops (re-routing the tubing so you don't need elbows and such things)
b) Improving the pumping capacities.

As what gives more performance in a block is the "speed" of the water (which depends on the flow only), the place in which you've got the highest pressure drop just doesn't matter at all because pressure accounts as a hole.

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Originally Posted by shazza

I like to read the debates.

But, the only way to really know if it makes a difference is to try your loop using different setups. Perhaps it takes some work, but it's easier on the brain than reading all this technical stuff :p:

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I agree to a point. I think the best way is to read thru, gather what seems to make sense to you personally, and then try those suggestions and see if they work for you.

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Originally Posted by Movieman

But my friend that is how we learn.
I have my specific ideas on the way to do things but I keep an open mind and when someone posts I read and consider their opinion.
I may not always agree but I do consider what they say.

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I totally agree. IMO it doesn't matter "who" but "what". OFC, If I start a speech about whatever without proof to support it, then it's purely BS (as I'm nobody in the water community). But, would it be Martin, it would be a different story...although we all know that what he says is based on his experimental analysis so I don't think he will ever start to say something without knowing where his basis is. What we should care is wether what is being said has some "basis" to be proven on, not just believe in those who have the most reknown (not saying they are wrong, deffinitely, just saying they may be other people who knows what they are talking about without needing to be part of the scene).
Just my 2 cent.

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Originally Posted by prava

I totally agree. IMO it doesn't matter "who" but "what". OFC, If I start a speech about whatever without proof to support it, then it's purely BS (as I'm nobody in the water community). But, would it be Martin, it would be a different story...although we all know that what he says is based on his experimental analysis so I don't think he will ever start to say something without knowing where his basis is. Just my 2 cent.

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I agree and martin's posts are always read here.
When I did my first WC setup I went and read thru the WC section and gathered all the info I could from people such as him.
I took my time, assembled that back in August 2007, and since then I think I added app 2 ounces of fluid and thats it.
Still maintains the same temps it did when first assembled and that to me is the proof of concept.
Excellent temps long term with minimal maintaince needed.

All I was saying was that martin summarized it very clearly and concisely. I apologize if I offended you but I certainly did not intend it - perhaps my statement was poorly worded.

Maybe I am just spewing what others have said but here is my understanding of it all from a physics based standpoint.

You have X amount of water moving at Y volume per unit time - The water also has Z velocity. When that water is in the tube it is in its base state; moving at 1 Y and 1 Z. When that water flows through a smaller space than the tube its velocity (Z) increases because it is a closed loop the flow rate of the water (Y) is constant - the pressure drop is a function of the amount of energy it takes to increase the velocity of the water through that area. Considering this it is very easy to conclude that if flow rate Y is constant throughout the loop than no matter where a given block is in a system the pressure drop through the block produces the same water velocity and thus the same cooling results. Mind that this is completely independent of the thermal variables.

the closed loop flow system is very analogous to an electrical circuit in this way of relating pressure drop to energy and the total head pressure of the pump compared to the total pressure drop of the blocks. The outlet of the pump is the area of highest potential and the inlet of the pump is the lowest potential.

okey i think i realized where everyone was confusing me.
When i say PRESSURE, i more mean displacement pressure as in head pressure, or impact velocity is a better word for it.
I dont mean pressure as in PSI pressure.

Meh... i think thats why everyone was getting me confused. And for a while i even got confused.

About the 2C benifit ONLY on the KL-350 block, im having Skinnee and Vapor retest this.

Naekuh, read what I posted above - you could have the most restrictive block imaginable and it wouldnt change those facts. I dont think that there is a difference between pump before cpu block because flow rate is always constant

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Originally Posted by SNiiPE_DoGG

..it is very easy to conclude that if flow rate Y is constant throughout the loop than no matter where a given block is in a system the pressure drop through the block produces the same water velocity and thus the same cooling results.

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No, and this is the point I have been trying to make. The velocity will VARY depending on where the block is placed in the loop.

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Originally Posted by SNiiPE_DoGG

Naekuh, read what I posted above - you could have the most restrictive block imaginable and it wouldnt change those facts. I dont think that there is a difference between pump before cpu block because flow rate is always constant

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Swiftech Storm Rev. 2

:yepp:

snipe you remember that block right?

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Originally Posted by nikhsub1

No, and this is the point I have been trying to make. The velocity will VARY depending on where the block is placed in the loop.

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please tell me how the velocity varies if the volume of water is not compressed?

you have X units of water in and X units of water out of the block - its velocity inside the channels or pin matrix of the block changes but the velocity on either side of the block is equal. (in the tubes)

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Originally Posted by NaeKuh

Swiftech Storm Rev. 2

:yepp:

snipe you remember that block right?

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I am still using Storm Revision 1! Flow rate is constant, but as flow area decreases, velocity increases to maintain flow rate. As velocity increases, so does the pressure drop.

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Originally Posted by SNiiPE_DoGG

please tell me how the velocity varies if the volume of water is not compressed?

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by changing diameters of tubing.

You cant say if holding flow rate constant, water will travel the same speed from point A to B in a 1/2 inch tube vs a 1/4 inch tube can you?

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Originally Posted by alacheesu

Physics seems to anger a lot of people.

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i completely agree, and i will stand down and admit im wrong if you can show me mathmatically or via phsyics. :T

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Originally Posted by NaeKuh

by changing diameters of tubing.

You cant say if holding flow rate constant, water will travel the same speed from point A to B in a 1/2 inch tube vs a 1/4 inch tube can you?

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I said that flow rate stays constant between different restriction levels - therefore velocity is variable and changing.


the fact of the matter is the pump puts out X litres per minute and must also take in Y litres of fluid per minute where X=Y.

therefore FLOW RATE (volume per unit time) is always constant in the closed loop.

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Originally Posted by NaeKuh

i completely agree, and i will stand down and admit im wrong if you can show me mathmatically or via phsyics. :T

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I know. You're always friendly, helpful and never too proud to admit you're wrong. That's top class in my book.

My comment wasn't really directed at anyone though, just a general observation. I think this is an interesting thread, and if it ends in some test results it will be even better.

OOPS... i didnt read your last part carefully snipe..

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Originally Posted by alacheesu

if it ends in some test results it will be even better.

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My tests will probably be ready in ~7 days if I wait for the KL-350. Or I can test with a FV2 + 3.5mm nozzle (restrictive as heck, but who knows if it exhibits this behavior) or with an Apogee GTZ (less restrictive, but confirmed to love flow).

okey physics arguement... i understand flow rate is constant....

Then answer me this.... when you turn your system on, why does your res water level drop?

Physics says water level shouldnt drop no? because you need X liters per min though that tubing to get X liters per min out?

My head is about the blue screen right now. :rofl:

I always figured that was a case of some sort of micro-expansion of the tubing, since the system was suddenly under pressure. I'm just guessing, though.

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Originally Posted by RayderR6

:ROTF: I looked in here and 7 posts in I thought the OP must be really confused by now.

Oh well, just like life, get all the info you can and then sort it out.

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LOL not confused although I certainly never exepcted it to turn into such a lengthy discussion. I think in the end if so many people disagree then there really is no true right way, seems like the conventional way is res into pump into rad though so I will just leave it like this and perhaps next time i redo it will try the pump directly into the block and see what happens but I gather it's really nothing to lose any sleep over which is a good thing :up:

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Originally Posted by MpG

I always figured that was a case of some sort of micro-expansion of the tubing, since the system was suddenly under pressure. I'm just guessing, though.

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I have been asked by a friend the same question NaeKuH asked above and I never though of this possibility.

The other explanation I thought of is that there is still air somewhere in the loop and it gets compressed when the loop pressurizes.

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Originally Posted by Vapor

My tests will probably be ready in ~7 days if I wait for the KL-350. Or I can test with a FV2 + 3.5mm nozzle (restrictive as heck, but who knows if it exhibits this behavior) or with an Apogee GTZ (less restrictive, but confirmed to love flow).

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Will there we go, thanks Vapor!:clap:

I've never been afraid of being wrong, in fact that's when I learn the most. Look forward to the results. Can you also possibly record flow rate if at all possible? I just want to see if there is a difference, if it's a difference in system flow rate as opposed to the pressure difference.

I believe the velocity of the block is the same regardless where it's in the loop (this should be correct if system flow rate is the same regardless)and performance should not matter where it's in the loop except for the minor water temp difference around the loop. I could be wrong though, perhaps there is some sort of dynamic with the pump that improves overall flowsystem flow rate.

Only way to find out is have someone test it and Vapor is doing that..:up:

Thanks!!

LOL... i know my friend just pwned me with that statement snipe. :rofl:

I seriously thought loop order played no role... when i tested the KL-350 i saw a change. I told honda about it, he reported he seen a change as well.

But i totally understand the agruement flow rate must be the same so vol. entering injector should be same regardless of where it is in the loop.

But, holding that same agruement, why does the water in the res drop?

and when you turn it off, why does the water level go back up?

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Originally Posted by SNiiPE_DoGG

I have been asked by a friend the same question NaeKuH asked above and I never though of this possibility.

The other explanation I thought of is that there is still air somewhere in the loop and it gets compressed when the loop pressurizes.

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I wondered about that possibility too, but I've still had it happen even when I'm 99% positive that the air's been flushed out of every corner of the loop.

The other little quirk is that pinching the hose while the pump is running will also change the reservoir level.:confused:

so how many licks does it take to get to the center of a tottsie roll pop?