The Science behind cooling (in computers)

Well, I was board, and I thought this might be an interesting subject.

Here we discuss the positives and negatives about different cooling techniques, and how they work.

Now this is what I know about the subject:

You can separate cooling in to big groups:
-Sub Temperature cooling
-Plus Temperature cooling

The most common is Plus Temperature cooling. It is cooling by removing the heat by spreading it out over large surface and then letting it dissipate in the surroundings. In other words Using a heat sink to enlarge the area, and sometimes use fans to speed up the dissipation of heat. The plus temperature stands for not being able too cool underneath the temperature of the surroundings.

The best (in most cases) is sub temperature cooling. This uses more complicated techniques to cool a object below the temperature of the surroundings. This can go via phase-Change, laser cooling, and a very big amount of ways that are only used in cooling gasses to liquid form.

In the world of Plus Temperature computer cooling, you have the following ways (note: there might be more, but I summed up the most common):

-Passive cooling
-Active cooling via air flow
-Active cooling via liquid Flow

Passive cooling is simply increasing the area of the object that needs to be cooled using heat sinks and heat pipes. It has no moving parts, and is therefore the most used in normal computing, as it makes the least amount of sound. It relies on good heat conductors to transport the temperature from the object to a bigger mass, allowing for bigger surface area, and therefore better heat dissipation.

Active cooling via airflow is actually just science talk for a heat sink with a fan. This is a usually more effective method than simply cooling with a heat sink, as a flow of air cools the heat sink. Also, moving air contains less thermal energy, and therefore can take up more thermal energy from the sink as still standing air. The shape of the heat sinks is usually different, as in passive cooling, the air needs to be able to go up (as hot air has a higher thermal energy, and wants to go up) and therefore should always be able to do so (the fins of the sink need to be vertical and the top must be open), but with a fan this is not so important.

Active cooling with liquid flow can be divided in to 2 different types. First of all, the best know: Water cooling. Water cooling actually simply relies on transporting the heat from the processor or other IC to a area where there is more place to fit a bigger heat sink. Although it is called water cooling , it usually uses other, non electrical conducting and high heat conducting liquids, as this is both safer, and more effective. This technique is now a standard in high end computers, but has been used in cars for a much longer time.
The second, less know in home computing type is submerged liquid cooling. By lowering the entire computer (except for hard drive and other mechanical data drives, like cd and dvd players) into a electrically non-conducting liquid, mostly mineral oil, you dramatically increase the area. usually this is combined with active cooling with airflow, only the air gets replaced by the liquid, to sustain a stable flow in the liquid. Sometimes, multiple pumps cool this liquid by pumping it into heat sinks, and cooling it. If you do not do so, you can only work in bursts, as the liquid will heat up, and eventually wont cool effective any more. By using the computer for say, 3 hours, the liquid will slowly increase in temperature. If you then completely power down the pc, the liquid is allowed to cool again. By cooling the liquid with heat sinks and fans, you can run a long-term operation. Most people that want to cool a pc like this fill a aquarium with mineral oil. This technique is used by supercomputers too, only here, the liquid is pumped at high speed though very big heat sinks at high speeds, allowing 24/7 usage. This technique is very liked with overclockers, as it doesn’t only cool the processor, but also cools the north and Southbridge, 2 parts often forgotten in the world of cooling.

Then you also have Sub Temperature cooling. When talking about computer cooling this can be divided in to 2 main categories:

-Phase-change cooling
-Liquefied gas cooling

Phase change cooling is a very old system, but only recently introduced in the world of computers. everyone has one at their homes, and you use it every day: a refrigerator. The principle is actually pretty simple. It uses the relation between pressure and temperature. By taking a gas/liquid at room temperature, and then putting it under very high pressure, without allowing it to escape, it heats up. by then sending it trough a heat sink, it will cool back to room temperature. As it is still under a higher pressure, you can let the pressure drop again, and so will its temperature. This way, the liquid can sometimes be cooled to -120°C. It is then sent to cool the CPU, GPU, whatever, with its very low temperature, and then returns to the compressor, to be depressurized, to lose its heat again.

Liquefied gas cooling uses a gas that has been cooled to liquid form (Nitrogen, and sometimes even helium). as these liquids have very low temperatures, they are very effective in cooling. The only problem with this, is that the vast difference between the liquid and the actual core have negative effects on a long term. Also, when your liquid turns to gas, you can't reuse it, and its therefore very expensive to use over long term. Due to those reasons, its only used in record braking attempts.


If you look at the visual differences between Sub and Plus temperature difference, you will notice that Plus Temperature has very big heat sinks, and Sub has a as small mass as possible. The reason for this, is that as Plus uses Air to cool, he bigger the surface, the more air, the better cooling. But Sub cools far beyond the temperature of plus, and therefore, the bigger the mass to cool, the worse the cooling is.

Some stuff about how heat pipes and stuff work will follow.

Nero

Ty. I learned something new. What kinda cooling have consoles if you might know. Same or is something different there?

the processors are cooled passive, but actually the entire console is a big cooler. The heat is also dissipated trough the motherboard, and the entire thing is heat sinked. I don't know about Xbox360, but the Ps3 is cooled with at least 4 fans.

Huh 4 fans? Most of PCs have 1 or 2 right? So PS3 must have big heat to use 4 fans...

No, The pc has more than 4 fans (if you compare pc with the power of a ps3). the differnce is that a pc case is mutch biger and mutch more open then a ps3 case. in a pc, you have a few case fans AND a cpu ooling fan. a PS3 only have 4 case fans, but as there are verry close to the actual cpu heatsink, you can almost consider it a CPU fan

Oh i think i get but what about the size of fans? That must matter i guess.

It does, but its not only that. the eficincy of the fann, the amount of blades, the speed it turns, are just as important as the size.

Omg, nobody else responded?

Seems you're the only one who gets this things

Anyway what do you think it's better to buy nero: Intel's I 5, or AMD's Black edition?

Well, that purely matters how mutch you want to spend. I think (but its best you check on the web for this one, we are talking about much money) that i5's are better, but the black editions are better for over-clocking as you ca change the multiplier of every core. Als do the AMD's come with handy overclock software, witch allowed you to acces your bios from in windows and make changes there.

Hey, thank you Nero, that was really interesting!
I learned a lot about fans and cooling
And btw, this forum section is great!

Yeah. Sorry Nero, for not replying. I don't know what to say but I read all your science posts.

Nero is freaking smart guy. Respect!

Adam Shootyperson wrote:

DieOrFail wrote:

NeverMind wrote:Nero is freaking smart guy. Respect!

Thanks for all the positive replys guy. It just reminds me that this is almost like a family here.
and btw, im not so smart. Ok, maybe a little bit , but i know a lot about sience, and the fact that i went to university till i was 29 could have somethin to do with that, but i just know a lot about think hat are interesting to me. There are a hole lot of other things i know nothing about.
Il post about heatpipes later today

Nero wrote:
Il post about heatpipes later today

I'll wait for your post Thank you for sharing your knowledge with us ;D

Nero btw what is your profession? I mean you're working somewhere?

I am professor in mathematics (algebra) and i teach at the universety of hasselt.

(note, this is a purely theoretical piece of information. The Actual working of a heat pipe is much more complex than this, but with this you will understand the basics)

A few years ago, all CPU coolers were direct mounted, in such a way that the heat sink was in direct contact with the top of the ceramic casing of the cpu. After some time people started to notice that at a certain point the size of the heat sink didn't matter anymore, as the copper, that is suppose to conduct the heat, couldn't transport it as fast as the heat source created it. The reason for this is that the contact area between the CPU and heat sink was constant. (the Intel 1366 socked has a contact are of 36*36mm).
To solve this problem, a new solution was searched. It needed to transfer heat faster than copper, but he only know material capable of this is very pure machined diamond, and even that wouldn’t be fast enough. So they had to look for a other way, not by heat conductivity, but by mechanical movement.
To the eye, the solution looked like a simple copper or aluminum pipe, sealed off at both ends. But in the inside it’s a lot more than that. The pipes are usually made under (near)perfect vacuum, and are made out of 3 layers: the outer pipe, usually copper, an inner wick and a vacuum cavity. First they build the pipe with these 3 layers, and then the pipe is filled with a fraction of a percent by volume of working fluid, called coolant chosen to match the operating temperature. Due to the partial vacuum that is near or below the vapor pressure of the fluid, some of the fluid will be in the liquid phase and some will be in the gas phase. It is the 2 phases that make it work. The liquid will soak the wick, and the gas will fill the cavity. When one side is heated, and the other is not (this is vital to make it work, its worthless otherwise) the gas will take up the temperature, and therefore it will increase in pressure at the hot side. as the cool side has not changed in pressure, the hot gas will flow to the cool side, giving off its heat there. It will turn liquid, and get soaked into the wick. At the hot end, the liquid stuck in the wick will also turn into gas, and the process starts over. This movement created by the heat itself is the most efficient self sustaining heat transfer circle.
The main limitations of this are that the heat pipe has certain working conditions, and it will completely fail to work outside of these temperatures, as all of the coolant will either be liquid and soaked into the wick, or it will all be gas, and the only thing conducting heat is the copper tube. As most heat pipes are constructed of copper (a metal with high heat conductivity), an overheated heat pipe will generally continue to conduct heat at around 1/80 of the original conductivity. Most manufacturers cannot make a traditional heat pipe smaller than 3mm in diameter due to material limitations (though 1.6mm thin sheets can be fabricated). Experiments have been conducted with micro heat pipes, which use piping with sharp edges, such as triangular or rhombus-like tubing. In these cases, the sharp edges transfer the fluid through capillary action, and no wick is necessary.

The main reason for the effectiveness of heat pipes is the evaporation and condensation of the working fluid. The heat of vaporization greatly exceeds the sensible heat capacity. Using water as an example, the energy needed to evaporate one gram of water is equivalent to the amount of energy needed to raise the temperature of that same gram of water by 540 °C (hypothetically, if the water was under extremely high pressure so it didn't vaporize or freeze over this temperature range). Almost all of that energy is rapidly transferred to the "cold" end when the fluid condenses there, making a very effective heat transfer system with no moving parts.

Nero wrote:I am professor in mathematics (algebra) and i teach at the universety of hasselt.

Algebra is the only cool thing in Maths
Rest sucks and is TOOOOOOOOOOOOO abstract, in my opinion

Hey, that was very interesting to read
Thank you Nero, for your great posts!
I learn a lot in this forum

How do you know all those things Nero ? Do you take them from the web ? Do you ask Science teachers in your university ?

Adam Shootyperson wrote:How do you know all those things Nero ? Do you take them from the web ? Do you ask Science teachers in your university ?

I do both, and i read a lot of books. Anything else that is part of cooling you want me to go further into?

And just a interesting fact: Did you know a overclocked intel i7 can heat up from 20°C to 100°C so fast that the air underneath "explodes" in the suden change in temprature? It can destroy your motherboard, and kill the procesor, but it looks realy cool( for the 1.5 seconds it takes)

Nero wrote:
And just a interesting fact: Did you know a overclocked intel i7 can heat up from 20°C to 100°C so fast that the air underneath "explodes" in the suden change in temprature? It can destroy your motherboard, and kill the procesor, but it looks realy cool( for the 1.5 seconds it takes)

Now I know it
Weird thing, but really interesting^^

xD