Quote by Dix Dogfight

"Therefore we can conclude that low or high flow doesn't produce big/small temp differences of the water in the system.
Therefore any BS about faster flow in rad makes smaller tempdiff and thus produce much better cooling is a load of crap." end quote

Clarify something on your stance. When you state temp differences of the water, what are you comparing the water temp to? The ambient temp or the cpu temp or the inlet/outlet temp of the rad or block? If you mean high flow doesn't produce small temp differences between the inlet/outlet of either the rad or block then you are sadly mistaken.

gone_fishin:
I'm talking about the tempdiff between inlet/outlet.
And how can i be "sadly misstaken" when simple physics say so?

Have you actually measuerd the tempdifference between inlet and outlet? Or can you show me where the simple formula is wrong please.

EDIT:
Hmm I just realized that a flow of 2L/s is actually ALOT.
EHEIM 1250 produces 0.3 L/s with no resistance.
so lets take 0.1L/s instead which gives a deltaT of 0.5 which is still to small to make a difference and remember that this is with a 200W heatload.

In my testing a rise by .5C in the water changes the cpu temp. I'm getting a through system flow rate of 360gph (1gal = 3.9liter) so in liters that's 24lpm or .4lps. An average system usually gets 70 - 80gph or .08lps
You're trying to solve something by equation, but I have a real high flow system which keeps the water outlet temps only 2.5C higher than the room ambient at full load, overclocked.
Higher flow is better for watercooling whether it's in a nuclear powerplant, a car, or a computer. Read the third link that gmat posted a few posts back, very clear and informative.

2 notes
1 - 2l/s is an amazingly high flow. Reaching 0.5l/s is already uncommon. Usually we got about 100l/h in our systems that is 0.2l/s, that with a *very* good pump such as the E1250.

2 - If you plan to include inlet vs outlet temperature differences in your equations, do so but properly. You must take the logarithmic (ln) sum of those temperatures.
I'll save you a lot of work and headaches by telling you higher flow leads to better results (higher transfer rates).

(edit) oh and thanx to gone_fishing for the experimental figures :D

Ahh..., another day at the office. Another day to bitch about differences in flow-rate that 90% of us don't have the tools to measure (myself included) to get our CPU 1/2 a degree cooler.

A pump will always produce a finite/constant amount of pressure (unless you start altering it's voltage or something, but thats beyond this discussion) - regardless of the volume of water it is pushing, or how many blocks, rads, and other things are attached to the pump that is trying to stop the flow.

Once you know how much pressure the pump is creating, and how much resistance to flow the system will exert, you can calculate the volume of water that will move through the system. Obviously when there is no resistance to flow (pump sitting in a bucket with no tubing) the volume of water moved will be large. But the pump doesn't magically change the way it reacts to backpressure the moment you put it into an in-line system with some restrictions - it still tries just as hard as it ever has to move water (same pressure exerted on the outlet), though again obviously less water moves.

I'm not disputing what you are saying, just trying to clarify it. Our pumps react the same whether they are in a bucket with no resistance, or pushing water through a cooling loop that involves 10 computers with 10 blocks and 10 rads. Just that the ~5 PSI of pressure that our pumps provide doesn't move much water when you put that kind of restriction on it.

If you have a short, voltage does not drop to zero. The battery continues to supply a voltage to the circuit. Without voltage no current would flow, without current flowing your wires would not melt and fuses would not blow. And if that was true, we wouldn't need circuit-breakers and such to protect against shorts. Though - with a short in the circuit it's likely that the battery or one of the connections to it will quickly fry. Once that happens there is no longer a complete circuit - now voltage is zero.

Ah, but you forget, there is resistance in the wire which allows the current to flow. If there were a way to have a PERFECT no ohm load, then there would be nothing on the voltage.

There is a chemical reaction occuring in the battery that produces a voltage. Simply connecting the 2 terminals of the battery (even with a perfect 0-ohm load) does not magically stop that chemical reaction and dispell the voltage. A 0-ohm load would fry things, not get rid of voltage. Of course, it would be virtually impossible to measure the fact that there is no voltage, because a 0-ohm load would short your volt-meter as well

Yes, but there is still no such thing as a 0 ohm load. My fluke meter will measure resistance within its own test leads.

Maybe I can shed some light...

0 ohm = full load = closed circuit = short = superconductor

infinite ohm = no load = open circuit

Batteries have the potential to provide 1.5V (AA). The potential is there, wether it is used or not. If it is used, it can be measured. If it is not used, then it is just potential, but is still measured in volts.

A battery can only supply so much power. If it is shorted, then the voltage would drop some, as the short tries to draw everything out of it. The voltage would drop to where the amperage is high, but to where the maximum power is outputed. (outputed?):D

Batteries also have an internal resistance, but I guess that doesn't mean anything here.

Very interesting discussion - check out the overclockers.com board for some more if your a glutton for punishment.

Increasing the water flow rate through the rad does one thing, and one thing only. It increases the heat transfer coefficient between the coolant and the walls. This in turn decreases the delta-T between the coolant temp and the radiator wall temp required to 'push' a given amount of heat into the rad/fins.

Generally speaking however, the delta-T between the coolant and the walls is pretty small to start with. If you think about it, the radiator has a much larger internal surface area than the WB, and will thus have a much smaller delta-T as well. I would be surprised if for a 100W load the coolant to wall delta-T exceeded 2C in even a small radiator. I would bet the delta-T is lower in most setups.

So, the best that can be hoped for by increasing flow is to reduce this delta. Even with a 2C delta and doubling the heat transfer coefficient, the net change is 1C - not a lot. Note that if the CPU load is not changed, there will be no change in the heat actually dissipated by the radiator. But the heat will be dissipated with a lower coolant temperature. Since the CPU temperature is directly related to coolant temperature, this will lower CPU temps (in addition to any CPU temp reductions directly related to the increase in flow in the WB).

The whole concept of temp increase/decrease of the coolant as it passes through the block/rad is a red herring - its pretty much irrelevant. Yes, an increase in flow will result in a smaller coolant temperature change. But as described above, the change is minimal to start with, and is certainly much less than the coolant temperature increase above ambient at equilibrium conditions (in most setups anyway).

gmat - LMTD is a little over the top here - the temp change in the fluid is small enough that approximating it as constant won't introduce significant error.

gmat:
Heating up a specific amount of water with a constant heatload produces a LINEAR rise in temp. If you think you somewhat trick that into beeing logarithmic I suggest you restudy your thermodynamics.

I didn't make any contradictary statement that I can recall.

And please stop asuming all others in theese foums to be total morons. There are actually alot of intelligent people here. That doesn't get a headache over a few differential equations like you do.
Some of us actually work with them all day long and are happy and smiling anyway.

gone_fishin:
Not trying to solve a problem. I'm trying to redirect our joint efforts on what matters and kill a few general "thinkerrors" that that a few persons do.


Again I newer made a contradicory statment.
I stated that the tempdiff as a function of flow has a small impact on the cooling.

Higher flow is better but because of other factors.
NOT because it makes a lesser tempdiff in the WB.

Dix Dogfight,

I think if you are going to have an attitude, learn to clarify a bit better.

Higher flow IS better because it makes a lesser tempdiff in the WB. Not tempdiff as you are calling it (difference between inlet and outlet temperature) but tempdiff between the coolant and the WB itself.

Tempdiff from inlet to outlet is always a function of heat input and flow rate only. As I said earlier, using it in this discussion is a red herring.

Thanx noSoup for replying :)
And thats the one that needs to be logarithmic in order to be included in the general heat equation (see formulaes above). That's not a trick from me, i'd like all things in life to be as simple as 2+2, but they are not. I wont repost any more formula, please refer to the links i provided before.

Yes !
It's a purely local and dynamic effect which is irrelevant here. (would be relevant from a "rad design" point of view, where one wants to optimize rad design... OT here).

1 - if you're here to flame ppl and dont understand humour go to [H] you dont belong here.

2 - actually i hate diff. equations and i hate those pesky thermodynamic laws. One needs to live with them though... Thats just a matter of taste, just like some ppl hate coding in assembly...

Cova:

Yes I agree with your clarification. I just couldnt put it into words that well yesterday :)

gmat:

I am not sure about this but I have a feeling that NONE of us like Differental Equations (Lord knows I hate them!!! :) ) However your right, we do have to deal with them unless we all want to stay in "theory" world.

As for the faster flow throught a radiator = more heat disappation; I am still not convinced. Could be true but still has some holes in it.

One other thing. I have been reading around the threads and mentioning that we need to heat the water before it enters the radiator in order to make the radiator more efficent.....
Here is my take on that: YES a radiator WILL be more efficient the higher the Delta-T between ambient air and the water temp. However, making the radiator more efficent by heating the water more than necessary only adds more heat to the system and thus heats the whole system up. This is obviously bad; heat = bad :) Our radiators in our system WILL only be running at say 10% efficency because we want our water temps AS CLOSE TO AMBIENT AS POSSIBLE!!! A radiator running at say 50% efficency could remove say 2 degrees from a 15 degree delta-T water but that still leaves 13 degrees delta-T which goes right back to the block and gets more heat. OUr Radiators running at say 10% efficency will only be able to remove say 1 degree from a 8 degree delta-T which leaves only 7 degrees delta-T water.
NOTE: DO NOT HOLD ME TO THESE NUMBERS!! This is for theory example ONLY! Just to give us an IDEA of what is going on, not the actual figures.

Alright another wave of friendly flames come forth! :)

Qote by Dix Dogfight,
"Again I newer made a contradicory statment.
I stated that the tempdiff as a function of flow has a small impact on the cooling.

Higher flow is better but because of other factors.
NOT because it makes a lesser tempdiff in the WB."end quote

I still don't understand what you are trying to convey.
You state that higher flow makes a lesser temp diff in the wb but that's not why higher flow is better.
In my observance higher flow keeps the water temp lower so as it enters the block there is a greater potential for the water to absorb heat. If you run ice water through the waterblock then the temps will go down in the cpu so if higher flow causes lower water temps to enter the block is this not the same thing?

Hehe thats why CFD and fast computers exist :)

Well look again:
http://www.stewartcomponents.com/adv...tem_basics.htm

They explain it all pretty clearly. Obviously watercooling has been thought about in cars long before PC's.. And i'm pretty sure these ppl know what they're talking about. Dont they ?

You're probably getting this from mostly my posts scattered around the board - but you're misinterpreting what I've been trying to say (and it really should be the topic for another thread)

Our rads run really inefficiently because we have a low delta temp between the water and ambient air. To get the rad to dissipate more heat (be more efficient) we need to increase that delta, but by doing so we also increase the temp of water passing through the CPU block, which is a bad thing. This is the basic water-cooling dillema - we need cold water in the CPU, and hot water in the rad, and in a typical computer cooling system, the water is within a couple degrees of the same temp everywhere in the system.

But I never said I want to heat the water - why would one start putting excess heat into the system that is not required. I want to move heat around in the system, I just haven't figured out how to do it yet.

My only problem with that argument Gmat with that link is that.... those are cars and engines running at temperatures that we never want to get even close to.

Our systems run at much lower temperatures and much closer to ambient than a car radiator system runs at. For a car cooling system, I agree. But I think that with our system we need to also take into account that we have much lower heat sources, lower efficency radiators, AND water temps much closer to ambient.

That is where I am running into a problem with that argument.

Cova:

Clarification recieved and acnowledged! :)

And whats the difference with cars ?
1 - our rads are the same
2 - pumps have about the same rate
3 - car cooling gets less efficient due to boiling water problems. But one wants to avoid this in most engines...
4 - from an engineering standview those systems are *exactly* the same, same formulas, same setup, same problems, etc...
Please explain clearly the difference.

Dont forget the Q=UAdT ...

(edit) hint: our dT is lower. That means our Q (heat tranfer) is lower. And so what, work at a given dT and see what reducing U (direct factor of flow) or A (area) does to Q...

What? Who hates coding in Assembler?

I'm reviewing everyone's answers, and I'll post something later. Today is not a good day:confused:

No, no, no, no, no!

Increasing flow does not increase heat dissipation! It can't. At equilibrium, the rad always dissipates the same amount of heat - the amount added by the CPU.

What increased flow does is lower the delta-T between the coolant and the rad required for the heat flow. This decreases the overall coolant temp. It does not increase dissipation.

At equilibrium, the coolant temperature will drop by exactly the same amount in the rad as it increases in the block. Else we wouldn't be at equilibrium.

The best way to get the coolant temperature as close to ambient as possible is to increase dissipation to the air - either by increasing the fin area or moving more air. Sadly (since it adds to noise) this is the area most likely to show improvement in a WC setup, and the one most often ignored.

I think that when the flow is laminary, water flows much slower near the walls of the radiator than in the center of the channel. The effect on cooling is similar to adding a layer of thermal insulator (water does not conduct heat well without convection), which is bad. Increasing the flow rate is good because it can break the laminary flow pattern.

Is this what you meant, NoSoup? Or you had in mind something different?

Constant = arithmetic mean? Should be OK if the flow is not too low.

The only problem I see in trying to draw links between CPU water cooling and car engine water cooling, is the desired result of each, both use overkill style setups, but a car's watercooling is designed to keep the engine within a specific temprature range controlled by a thermostat, where as a cpu's water cooling is designed to keep the temp as close to ambient as possible.

I propose an easy solution to this whole debate, throw away your rads and use evaporative cooling instead :D ;)

Cova...what if one were to throw a couple pelts onto the rad, thus lowering the "relative ambient" of the radiator and increasing the deltaT. You obviously don't want to add heat to the coolant, as the point is to get it out of the coolant. So if you change the "relative ambient temperature, you increase the deltaT, the RAD works more efficiently, and I would think, cool the coolant below ambient since the "relative ambient" would be significantly lower that the "actual ambient".

gone_fishin:
Exactly

Here is an example (all numbers are made up, but will hopefully demonstrate what I mean)

Lets say you have a setup with no rad, using tapwater and never use the same watermolecule again. At first we have a high flow 0.3 of lps and a CPU temp of 30C. Then we lower the flow to 0.03 and the temp rises to 40C.
The equation shows that the rise in temperature in outletwater will for a normal CPU=80W be:
80/(4180*0.3)=0.06C
80/(4180*0.03)=0.6C
So the outlet water will be 0.54 degrees hotter with the lower flow and the CPU will be 10C hotter.
The mere increase in watertemp alone can't produce the higher CPU temp.
So the lower CPU temp can't be a result of the lower temp diff between inlet and outlet as many people tend to think but rather a effect of the WB having better thermal transferproperties at a higer flow.


gmat:
I never flamed anyone i simply asked you to stop assuming others not to understand all great things you have learned in school.
I learned a whole lot during my 8 years at the Royal Institute of Technology (Swedens version of MIT) so I know exactly what school's like and all the great thing you can learn there.
But telling everybody that I have the knowledge and don't share it isn't very productive.

Humor in my world isn't statments like:
I know a whole lot of stuff about thermodynamics but i'm not going to post them here because the are to hard to understand anyway. Just belive my word. Higer flow is better.
Statements like that are totally useless.


NoSoupForYou
On the subject of attitude:
Making a post clear and easy to read/understad produces a very long post and many ppl tend to ignore those. So in keeping a post short many ppl will read it but at the price of everybody not understanding all. So making the first post short but provocative (using words like BS and crap) usually produces a high number of replys and then try and elaborate after that usually works.
Some ppl on the other hand (not referring to anyone) simply sees the words BS and crap and therfore feel offended and don't take their time to read and understand what the poster want's to say.
Which is a problem with this type of posting approach.

Everyone=all ppl posting here:
One thing to remember is that not everyone here has english as their default language. So please try and read post's twice because we that don't know exactly what word to use, to make the message come forward the way we intended, might seem to have an attitude but perhaps only lacks the finer tune of the english language.

Well I'll leave you guys alone for the moment (4 weeks of vacation starting in 5h. So I'll just check back in in august to see if there has been any progress. ;)

cheers

The total heat transfer through the block is the continous sum of heat transfers in finite elements constituting the block.
No matter how you put it, there's a close relationship between inlet / outlet temp diff and total heat coefficient.
But what we said earlier (and repeated it) is we dont care about inlet / outlet temp diff ! From our point of view (watercooling systems) it's only a side-effect.
And wasnt the thread topic about *pressure* ? (on that i'd want to hear fluid dynamics experts)

Calling ppl "morons" and trolling that way aint very nice, dude.

So you never flame anyone ? ah.
So far:
* i've posted all necessary thermodynamics equations (so far only one is of interest i admit)
* i've posted links where they are explained thouroughly
* did you read the thread ? I doubt it. Read before flaming... (where did i say "I know a whole lot of stuff about thermodynamics but i'm not going to post them here" ???)

Doesnt that sound like a contradiction with your previous statement ? hmmm.
Anyways on pro/forums ppl DO READ long posts. Until now the level of these forums have been quite high.

I first stated that "thermal laws" simply say that higher flow is better. I never sh*tted on anyone or called anyone a "moron", neither i made a statement that i had "superior" knowledge or such BS.
Then ppl answered (politely and friendly) and i made more thourough statements (friendly, and politely again).
Then i posted some links to these formulaes to support my argument. (did you notice that ?)

I just try to be helpful and bring my small knowledge to these forums since i like the ppl here. And while i'm at work i cant take the time to dig into thermal equations, so i try to stay brief.

Note: i enjoy flamewars as well, so come on, i've got an integral flameproof suit.

That is a wise statement, and a base of netiquette. For your information calling ppl "morons" wont help you getting friendly answers...

NOTHING THAT FOLLOWS IS ANY KIND OF FLAMIN ON ANYONE OR ANYTHING. AND I HOPE THAT IT CLARIFIES SOME ISSUES.
AND WITH THIS I END MY POSTIN IN THIS THREAD (because of earlier stated resons) AND HOPE IT WILL BEER SOME KIND OF FRUIT TO BENEFIT US ALL.

gmat:
Here is what I wrote on the moron subject
.
I never stated you to be a moron If you read it again I hope you will see that. If you still take it personally I can only apologise.


So we are in a agreement then.
My first post was an attempt to explain (for anyone interested) why lesser flow doesn't produce a much higher tempdiff and that it is not the major contibutor to the lesser performance that a lower flow does.

Now do i take this personally or do you mean that they still are. Or you might mean a whole other thing.
I can choose read it as a flame or not. Do you se what i mean when I say that small differenses in language = how I choose to write. What words I use can make a world of difference in how the recipient interprets it.
If the recipient onyle reds through it fast and don't take into account that we are from different parts of the world then these kind of misshaps will continue to happen.

I wrote:
gmat wrote:
I can only assume that my message didn't get through properly again and was interpreted as a flame.

Wow, I can't believe we are still debating this.

It is clear - inlet to outlet temp differential is a function of the heat input and flow rate only. That's it.

Nope. Well, not really anyway :). There is correlation, but no causality.

If you have a higher flow rate, you will have a lower inlet/outlet delta-T. That's true. And if you have a higher flow rate, you will have a higher heat transfer coefficient. Also true. But to say that a lower inlet/outlet delta-T causes a higher heat transfer coefficient is technically incorrect. It is the higher flow rate that causes both the lower delta-T and the higher heat transfer coefficient.

And Dix - yes, maybe a couple of opening flames generates more interest in the thread. But it's bad interest. Look at the last few posts - little information, mostly flames and explanations of why a flame wasn't really a flame.

It's a sad state of affairs when a post more than 10 lines long gets ignored. But at least those that might benefit may read it.
Please, someone read my earlier post, and if you have a question ask it. But it seems like the concept has fallen on deaf ears.

No....I have read it all :)

And it is very interresting :)