Pump pulling from CPU does it make a difference?

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05-10-2009, 08:53 PM
prava

Quote:

Originally Posted by DeathWalking

Oh my god, please tell me Gauss' Law does not apply to fluid dynamics! :para:

Gauss, it was Gauss!! If I don't remember it wrong this is what our physics teacher told us, that the same rules apply for liquids and current, and so we use the same law (Gauss' one).

Quote:

Originally Posted by Martinm210

We only need some pressure to keep our tubes formed, otherwise what we really need is "Pressure Difference". That's what pumps give us, a pressure difference from the outlet back to the inlet, and it's this pressure difference that's the form of energy that moves the fluid around. That's all it is, the pump produces the pressure differential, then the blocks and rest of the system absorb that pressure energy as the fluid moves around the system. Pressure difference is the only thing (Besides gravity) that can move a fluid.

Even in an open loop system, the pump is still just producing a pressure difference, but there is a distinct difference. In an open loop you can gain or loose static pressure energy. If you pump water up 100' into a tank, it now has alot of stored energy in the form of elevation. In a closed loop, any water that is pumped up, comes back down so static pressure gains and losses net 0. All we're left with is pressure drop (difference across blocks, etc due to friction), and pressure gain (difference across the pump). Both of these have a performance curve. We just refer to the blocks/fittings as pressure drop. And it's also more common to "Think" of pump as pressure head. But in the end what's really going on is pressure differences, the actual pressure numbers themselves are not important, only the difference.

Thx Martin for your time, I still remember the very first time I came across your reviews and i was like "No way, those graphs have to mean something but yet I've got no clue about what the hell they do mean". Now everything seems a bit more simpler...thanks to you and other people who invested their precious time trying to show the others how do thinks really work.

Ok. So pressure is used in order to make the water "move" around the loop. If we get it to 0, then there is no flow, in some ways it's like friction because it opposes to the movement...yet it depends on it to be there (as there is no friction is there is nothing trying to move).

OK, to sum up and to check if i've got everything alright (if I haven't I'm gonna commit suicide, i swear :stick::stick::stick:
So, when you choose a pump, the only think that really matters is the flow rate...and the pressure if you would exceed it, otherwise it just doesn't matter at all. The shortest the circuit the better because you reduce pressure drop (as everything in the circuit reduces pressure). And, the other doesn't matter at all cause the flow is constant throughout the loop (BTW, you said that rad after pump is a good idea because doing so the cpu block will get the very coldest water... but now that I think about it, the difference might be totally negligible as the pump would only put about 20W in the water, which is nothing compared to all the other heat other blocks put in...).
Mmmm which means that a D5 is the way to go if you aren't going to put many blocks or they aren't really restrictive and the DDC is better if you are putting plenty of blocks or a hell of a restrictive one. BTW, is there any way to mount a loop (a possible one, not one with 10 blocks) with a D5 in a way that the total pressure drop exceeds the head pressure and so water just doesn't flow? Because if there isn't (or at least not one that you will ever do) I don't see the point about not buying the D5...

Quote:

You'll find that most of the highly debated topics are generally those that are either hard to measure, nobody has tested them, or they are generally insignificant. I didn't believe it much myself until I install a thermal probe before and after my CPU block. I got bored looking at the same insignificant difference. Temp out was always just a couple of tenths of a degree higher than in...not very interesting.

But that's something that doesn't need rocket science to understand (if you compare it to all the other stuff) :rofl::rofl: If you just take in account how much water flows at that point it's pretty clear that you will need a hell of a good instrument to measure the difference between inlet-outlet temperature.
I guess it's the only part I could understand precisely :ROTF::ROTF: (not much, but hey, its a start).
05-10-2009, 09:53 PM
Erasmus354

Quote:

Originally Posted by prava

OK, to sum up and to check if i've got everything alright (if I haven't I'm gonna commit suicide, i swear :stick::stick::stick:
So, when you choose a pump, the only think that really matters is the flow rate...and the pressure if you would exceed it, otherwise it just doesn't matter at all. The shortest the circuit the better because you reduce pressure drop (as everything in the circuit reduces pressure). And, the other doesn't matter at all cause the flow is constant throughout the loop (BTW, you said that rad after pump is a good idea because doing so the cpu block will get the very coldest water... but now that I think about it, the difference might be totally negligible as the pump would only put about 20W in the water, which is nothing compared to all the other heat other blocks put in...).
Mmmm which means that a D5 is the way to go if you aren't going to put many blocks or they aren't really restrictive and the DDC is better if you are putting plenty of blocks or a hell of a restrictive one. BTW, is there any way to mount a loop (a possible one, not one with 10 blocks) with a D5 in a way that the total pressure drop exceeds the head pressure and so water just doesn't flow? Because if there isn't (or at least not one that you will ever do) I don't see the point about not buying the D5...

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.
05-10-2009, 10:55 PM
Jokester_wild

res>pump>rad>pump>cpu>gpu /end
05-10-2009, 11:08 PM
SNiiPE_DoGG

I thank martin for his time in sorting this all out :D

the rest of this thread is just pointless - people throwing around their unfounded opinions on the matter....
05-11-2009, 12:00 AM
Fragger

This thread has inspired me to change my loop from res>pump>cpu>gpu>rad>res to res>pump>rad>cpu>gpu>res. The idea is because I use a large bronze res it will dissapate more heat with the hot water entering it rather than the rad then res - at least thats the theory.......
05-11-2009, 02:30 AM
RayderR6

Quote:

Originally Posted by SNiiPE_DoGG

I thank martin for his time in sorting this all out :D

the rest of this thread is just pointless - people throwing around their unfounded opinions on the matter....

: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.
05-11-2009, 05:19 AM
Martinm210

Quote:

Originally Posted by prava

So, when you choose a pump, the only think that really matters is the flow rate...and the pressure if you would exceed it, otherwise it just doesn't matter at all. The shortest the circuit the better because you reduce pressure drop (as everything in the circuit reduces pressure). And, the other doesn't matter at all cause the flow is constant throughout the loop (BTW, you said that rad after pump is a good idea because doing so the cpu block will get the very coldest water... but now that I think about it, the difference might be totally negligible as the pump would only put about 20W in the water, which is nothing compared to all the other heat other blocks put in...).

Mmmm which means that a D5 is the way to go if you aren't going to put many blocks or they aren't really restrictive and the DDC is better if you are putting plenty of blocks or a hell of a restrictive one. BTW, is there any way to mount a loop (a possible one, not one with 10 blocks) with a D5 in a way that the total pressure drop exceeds the head pressure and so water just doesn't flow? Because if there isn't (or at least not one that you will ever do) I don't see the point about not buying the D5...

Not exactly, I was trying to explain pressure from the stance of loop order. When chosing a pump you really need to see the full relationship of pressure head vs. flow rate. Pumps refer to this as pressure head, so it's easy to confuse this as pressure by itself. The "Pressure Head" number is really the difference of pressure on the pump (outlet - inlet). This is called the Total Dynamic Pressure Head. The inlet will actually have a little negative pressure. So it is important to look at both numbers, but they are really just the two points on the whole curve. To really know how a pump is going to perform you need to see the whole curve. Some curves are a straight line, some are curved, and the shape of this curve can make a difference. Anyhow, don't disregard the pump pressure head. It sounds like "Pressure", but it's better to think about it in terms of "Pressure Rise" or "Pressure Difference", because it's this difference in pressure that's moving the fluid around. Ideally, pump specs would include the full curve, or at a minimum what pressure head is produced at 1.5GPM or somewhere in the middle of the curve.

Shortest circuit may not always be the lowest pressure drop. For example, you could remove tubing length and add a bunch of elbows and do more harm than good. Some elbows like the 1/2" nylon types with a 3/8" ID are equivalent in friction to 4' of tubing for example. For the most part how the tubing is setup and friction losses is pretty small and almost insignificant though, so I wouldn't worry too much, and just have fun with it.

Exceeding a pump to zero flow.

No, because as flow rate reduces, so does pressure drop. The pressure drop in the blocks and tubing depends on the flow rate. I find it pretty hard to put enough restriction in where you would bog down a D5 much below 1GPM. You can try it in the estimators, you might get it down as far as .9GPM or so, but it's pretty hard to get below that.
05-11-2009, 06:18 AM
nikhsub1

Quote:

Originally Posted by SNiiPE_DoGG

the rest of this thread is just pointless - people throwing around their unfounded opinions on the matter....

Excuse me? Nothing I have said is unfounded. In fact, it is all correct. Its posts like yours...
05-11-2009, 06:46 AM
Jah

NaeKhu how close are your pumps to the block when benching?

Assuming you have turbulent flow at the pump outlet you will need some distance in a tube to get back to a laminar flow, anyone have a estimate on this distance. I have a vague recollection that the transition from turbulent to laminar is some what "random" depending om a bunch of more or less hard to control conditions.

Any other ideas the turbulent flow from the pump entering the block, or is just NaeKhu and Hondacity breaking the laws of physics, I wont tell if you don't ;)
05-11-2009, 07:54 AM
Sadasius

I get a kick out of those humping the legs of others who they think are right but have no idea themselves. Despite the many ideas, theories, laws of physics and thermal dynamics we have no idea who is right until it is tested. I would be interested to know why jet plates were invented and inserts for the CPU blocks. Would these work better after the pump or after the rad? This should be one project next in line for those who would want to test it. Would be a simple test really. Just need to switch out the tubes and record the temps for the same given time the loop was running. Perhaps use a couple different blocks as perhaps both theories are actually correct and are block dependent.
05-11-2009, 08:53 AM
alacheesu

Physics seems to anger a lot of people.
05-11-2009, 08:55 AM
nikhsub1

Quote:

Originally Posted by Sadasius

I get a kick out of those humping the legs of others who they think are right but have no idea themselves.

Me too Sadasius.

Quote:

Originally Posted by Sadasius

Despite the many ideas, theories, laws of physics and thermal dynamics we have no idea who is right until it is tested. I would be interested to know why jet plates were invented and inserts for the CPU blocks. Would these work better after the pump or after the rad? This should be one project next in line for those who would want to test it. Would be a simple test really. Just need to switch out the tubes and record the temps for the same given time the loop was running. Perhaps use a couple different blocks as perhaps both theories are actually correct and are block dependent.

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.
05-11-2009, 08:59 AM
Hondacity

Quote:

Originally Posted by Sadasius

I get a kick out of those humping the legs of others who they think are right but have no idea themselves. Despite the many ideas, theories, laws of physics and thermal dynamics we have no idea who is right until it is tested. I would be interested to know why jet plates were invented and inserts for the CPU blocks. Would these work better after the pump or after the rad? This should be one project next in line for those who would want to test it. Would be a simple test really. Just need to switch out the tubes and record the temps for the same given time the loop was running. Perhaps use a couple different blocks as perhaps both theories are actually correct and are block dependent.

once i get more quick disconnects, this test will be easy, i'm pretty sure my theory will be proven right.

quick disconnects, and no remounts :D
05-11-2009, 09:38 AM
Sadasius

Quick disconnects might actually impede this test somewhat wouldn't it? I mean it is a restrictive device in between the pump and block.
05-11-2009, 09:54 AM
SNiiPE_DoGG

Quote:

Originally Posted by nikhsub1

Excuse me? Nothing I have said is unfounded. In fact, it is all correct. Its posts like yours...

Did I say "nikhsub1 doesnt know what he's talking about"? way to take everything like its directed at you....
05-11-2009, 09:59 AM
Waterlogged

Quote:

Originally Posted by Sadasius

Quick disconnects might actually impede this test somewhat wouldn't it? I mean it is a restrictive device in between the pump and block.

Yes it will.
05-11-2009, 10:13 AM
Hondacity

Quote:

Originally Posted by Sadasius

Quick disconnects might actually impede this test somewhat wouldn't it? I mean it is a restrictive device in between the pump and block.

Colder FFC :rolleyes:
05-11-2009, 10:21 AM
Waterlogged

Quote:

Originally Posted by Hondacity

Colder FFC :rolleyes:

Next time, specify before hand. Someone says quick disconnects these days and most ppl think valved type or Koolance. :p:
05-11-2009, 10:45 AM
nikhsub1

Quote:

Originally Posted by SNiiPE_DoGG

Did I say "nikhsub1 doesnt know what he's talking about"? way to take everything like its directed at you....

Then WTF does this post of yours below mean???? You pretty clearly said that no one but Martin knows WTF he is talking about.

Quote:

Originally Posted by SNiiPE_DoGG

I thank martin for his time in sorting this all out :D

the rest of this thread is just pointless - people throwing around their unfounded opinions on the matter....
05-11-2009, 10:50 AM
NaeKuh

Quote:

Originally Posted by Jah

NaeKhu how close are your pumps to the block when benching?

Any other ideas the turbulent flow from the pump entering the block, or is just NaeKhu and Hondacity breaking the laws of physics, I wont tell if you don't ;)

http://i125.photobucket.com/albums/p...i/IMG_1385.jpg

I have very very very little restriction on my cpu loop minus the cpu block.
The rad is a PA which has the lowest flow drop, the only 90 i have in the loop is dual pathed even.

I have more head pressure (dual DDC-2) then the average person.

And the KL-350 is one restrictive and hungry block.

Quote:

Originally Posted by Waterlogged

Next time, specify before hand. Someone says quick disconnects these days and most ppl think valved type or Koolance. :p:

:rofl:

i think the koolance is because of me..
05-11-2009, 11:48 AM
Sadasius

Quote:

Originally Posted by alacheesu

Physics seems to anger a lot of people.

That's because most of the people here are rather intelligent and to have their theories debated by another....well let's just say you might as well rape their mother. It is why tests are important and that false advice can then be stopped. We do try here to help and share our knowledge so that we all have some kickass rigs that the world envies. So let's stay on that track! :up:
05-11-2009, 11:51 AM
Movieman

Quote:

Originally Posted by SNiiPE_DoGG

I thank martin for his time in sorting this all out :D

the rest of this thread is just pointless - people throwing around their unfounded opinions on the matter....

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.
05-11-2009, 11:52 AM
Vapor

Quote:

Originally Posted by Sadasius

I would be interested to know why jet plates were invented and inserts for the CPU blocks.

To increase the velocity of the fluid at a certain point in the block. That, and some like the FV2's quad nozzle, are to direct flow to certain parts of the base.

Quote:

Originally Posted by nikhsub1

Then WTF does this post of yours below mean???? You pretty clearly said that no one but Martin knows WTF he is talking about.

I took offense to it as well...:shakes:
05-11-2009, 11:56 AM
Sadasius

Quote:

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.

+1 :up: "Without Order nothing can exist. Without Chaos nothing can evolve"
05-11-2009, 11:59 AM
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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