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CPU Convective Water Cooling
biso writes "The possibility of cooling a CPU with gravitational convective flow of water is here analyzed and experimented with positive results.
Many liquid cooling systems have been experimented by overclockers to better dissipate the heat from CPUs. The major part of these coolers is characterized by a relatively complex system requiring pumps or other active devices. Sometimes even liquid nitrogen is used. I built a simpler cooler, able to dissipate the same heat flux of a normal heatsink."
He's going to be boiling noodles in a minute
Banaaaana!
ok, i can see the extra bit of silence from not having a pump would be nice. but ... isnt a bowl of water on top of your computer just asking for trouble? something tells me this guy doesnt have cats.
I've built numerous different water cooled systems, and the $20 pump from the aquarium supply place is NOT the most complex piece. A good waterjacket for the cpu is by far the most complex and generally most expensive single piece, and also the one that is most critical for good performance. Still need the waterjacket in this design, so it isn't really saving anything...
It's cheap, reliable, odorless and environmentally friendly, and refills are available everywhere. I myself have been using a 78% nitrogen gas mixture at 14.7 PSI to cool all my computer components for years now. Where did I get the idea? I guess I just pulled it out of thin *SMACK*
I really think that phase change cooling systems are the future of the PC. Only with phase change cooling systems do you get high quality cooling able to remove the utmost heat away from a CPU and cool it to below freezing.
I saw a presentation by Intel last year in which it pointed out that modern CPU's emit more heat per area than molten lava, and they expect that within a few years they will emit more heat per area than the sun.
With these considerations passive water cooling is only a good first step and bound to be insufficient, even over the short term.
Abstract
The possibility of cooling a CPU with gravitational convective flow of water is analyzed and experimented with positive results.
Introduction
Many liquid cooling systems have been experimented by overclockers to better dissipate the heat from CPUs. The major part of these coolers is characterized by a relatively complex system requiring pumps or other active devices. Sometimes even liquid nitrogen is used.
My intent was instead to build a cooler able to dissipate the same heat flux of a normal heatsink, but without the annoying noise of the fan.
A first prototype was built out of a regular heatsink. Holes were drilled in the aluminium finning, and copper tubes passed through them. An aquarium pump provided the necessary pressure for circulation.
Figure 1. First Prototype--Front View
(picture)
Figure 2. First Prototype--Side View
(picture)
The system was silent and reliable. But with bigger pipes and a lower pressure drop would it have been possible to take away the pump? Simple calculations showed that it would have been perhaps feasible and a prototype was built.
Temperature on Heatsink Surface
Roughly:
Power to be dissipated: powd = 80 W
If the heatsink is a little copper box to put over the CPU, a reasonable value for the surface available at copper-water interface can be: surfc = 0.01 m2
The heat transfer coefficient on the water-copper boundary layer can vary from a few watt per square meter per kelvin if the flow is slow and laminar to more than 1 kW K-1m-2 when the flow is very fast and turbulent. If the coefficient is supposed to be: texc = 100 W K-1m -2
The difference of temperature on surface will be: delt = powd / (texc surfc) = 80 K
It appears that the water should boil on the surface of such a little heatsink, but radiation wasn't taken into account and the geometry of the box is complex, so it's not clear if there could be turbulence and with which effect. If necessary the surface could be enhanced with fins or by increasing the dimension of the equipment.
Convection
Supposing that the heatsink could be able to exchange the heat between the CPU and the water, would it flow through the pipes?
Power to convey: powd = 80 W
Length of the circuit branches between the CPU and the radiator on the top of the computer case: heigh = 0.8 m
Equivalent length of the circuit (we take into account the bends too): len = 2 m
Radius of the pipe: rdp = 9 10-3 m
Rate of change of water density against temperature: dct = 0.55 kg m-3 K -1
Water density: rho = 103 kg m-3
Water viscosity: eta = 10-3 decapoise
Specific heat of water: wsh = 4180 J kg-1 K -1
Gravitational acceleration: grav = 9.8 m s-2
Pi: pi = 3.14
Difference of temperature between ascending and descending branch: deltat
Difference of density of the water in the two branches: deltarho = deltat dct
Difference of pressure due to the difference of density: deltap = deltarho grav heigh
Volume of water conveyed per unit time: vot
Pressure drop in the pipe: deltap = vot 8 eta len / (pi rdp 4)
Power conveyed: powd = wsh rho deltat vot
Putting it all together: deltat2 = 8 powd eta len / (wsh rho pi rdp 4 dct grav heigh) = 3.4 K2
Everything should work with a temperature difference of less than 2 kelvin. Consequently the radiator isn't required to be very efficient.
SIRPAL-1 Prototype
The SIRPAL-1 prototype was made using a 5 mm thick copper sheet for the base, and 2 mm thick copper sheets for the walls. The edge of the square base is 55 mm long. Inside there are two plates 25 mm wide. One is vertically aligned, soldered to the base, to increase the exchange surface near the CPU, the other is horizontal, soldered between the input-output pipe fittings, to guide the fluid in the right direction.
A test was performed on a K6-2 450MHz which dissipates a power of about 25 watt. The ambient temperature was 18 celsius degrees. After a few hours the CPU temperature, measured by the PC board sensor, was at least 1 kelvin lower than when the fan is used. External surface temperatures: 19 celsius degrees on the pipes; 24 celsius degrees on the copper box.
A drop of ink in the water revealed a slow flow as expected. It worked so well that I think a more powerful CPU would be efficiently cooled too.
Figure 3. SIRPAL-1
(picture)
Figure 4. SIRPAL-1--Testing
(picture)
...using sponges as sound dampening material inside the case. Who knows, it just might save your computer when somebody bumps the frickin' table and dumps that bowl full of water over everything!!
Didn't I see that figure 3 photo in Die Hard with a vengance?
Trasformer oil is insulating and would not short-out anything. It could also cool the powersupply at the same time, without the inherint saftey risk water subjects us to.
...powered by water (or even antifreeze) could conceivably do two jobs: provide cooling for the cpu and produce power. It wouldn't have to be all that big either. It might not produce that much power, but probably enough to light a small desk lamp.
So far left, I'm right.
It's kind of ironic istn't it that CMOS PCs will eventually need the same plumbing as the TCMs they were supposed to replace.
Hey I had a 9021-721 MVS/ESA mainframe that used TCM's cooled by a 400psi cooling system. The great thing about the next gen CMOS mainframes was that even though one TCM was now replaced with 3-6 CMOS units, we didn't need a massive chiller system.
Oh well, guess everything will have huge ass chiller pumps now.
While I admire all of those who are willing to actually pipe water into their computers for the sake of keeping them cool, I am still more than a little frightened of this idea. Knowing me, something would end up leaking (probably through fault of my own) and my precious tower would go up in a ball of flame or some such. Rather, I choose to take your regular old air cooling and make it more effective. Through proper cable management, good airflow paths, a set of nice quiet fans, and the ability to control them with respect to how much they are needed, I keep my fan almost as cool as a friend of mine who does have a liquid cooling system, and with very comparable noise levels. If you're willing to do some work and set up a decent air-based system (and be willing to clean out the dust), there's no need to balance a bucket of water precariously on top of one's computer... : |
that picture of a bowel of water on top of an open pc tower case is not something I would necessarily run....
Bowels of water on his PC, this is something I definitely DON'T want to see!
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Yeah, and other times they go a little nutz and use Fluorinert
I know I have. I think eventually we'll see some commercially available sealed systems that use some liquid (probably not water because of its corrosive properties) and convection to move it around.
Something idiot proof and self contained with no mechanical parts, save perhaps a slower turning large fan to exhaust air.
So far existing heat pipes are not much more than a novelty. The wick style ones with alcohol as a fluid (mentioned here awhile back) look promising.
The giant skivved aluminum/copper blocks with the big ass fans aren't going to cut it, not just because of noise, but practicality.
I don't need no instructions to know how to rock!!!!
you could make the system safer by enclosing the bowel
You make your roommates happier when you enclose your bowel, too.
5 -- You just inherited $700 from your great-grandfather that's just waiting to be thrown out the proverbial case window
4 -- A loud smelly watercooling kit is the perfect complement to your neon light tubes
3 -- Why spend $200 for a brand new P4 when you can pay $500 for supplies and crank your P2 up 30 MHz?
2 -- That rock fountain you got for Christmas can be put to a much geekier use
1 -- To impress your classmates at Chubb Institute
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Alright - dude did this on a K6-2 450. They're about HOW many years old now?
I'd be much more interested to see him cooling an overclocked Athlon XP 2100+ with 1.9 vcore running at 2400 MHz - or something of the like - with the method in the article.
Ah well, I'm happy with my good 'ol pumps and radiator, myself.
You could just buy a *second* computer.
I'll form my OWN solar system! With blackjack! And hookers!
You may look here
:)
Without the need to implement that bulky bowl of water.
What? You guys are still using water? I found The Ultimate Cooling Device: Hilary Rosen (aptly named The Ice Princess).
I leave the sides off of my computer for better air flow and less dust collection, but mainly because I'm too lazy to put in case fans.
Since my case has to sit on top of my desk, this also gives me a little more space to put stuff (inside the case, out of the way of boards / wires etc).
What do I keep in there? First is the reciever for my wireless keyboard / mouse, the syncing cradle for my handspring visor edge, and a few important papers. Those are the things that don't really move.
The fun things in there are the mountain dew beer glass, the caffeine shot glass, and usually 2 - 3 open cans of dew. All have soda / caffeine in them and are actively used.
No, nothing has spilled yet, and yes, I do have cats. 3 of them. They know that if they go near the sacred tower, they get stuff thrown at them (usually a slipper, but on occasion a t-shirt if I find that first).
On a side note: I in no way have the balls to water-cool my case, other than replacing the cold soda every 30 minutes.
Work sucked, until it became unemployment, when it became slightly more tolerable. -Tet
Always good to see continuing advances being made in the field of compu-bong technology.
In Soviet Rush, today's Tom Sawyer gets high on you.
The thing that should be pointed out is this is how liquid cooling should have been done from the start. The reason their not is because most if not all of the home pc case cooling systems are things slapped together by people without engineering background in such things. Good liquid cooling systems are designed like this. There should be no pump to cool your cpu. The problem is to do it right involves doing some calculations which most don't do so they just use a pump. It's not a very hard thing as you can see by the article.
Now on a side note, if you like the idea of passive cooling loops Shuttle XPC cases now come with them. They use very similar ideas. You have liquid in a tube, when it vaporizes it rises to the upper radiator where it condenses and a fan carries the heat away and the water returns to the cpu side of the loop. Not sure if it vaporizes or just gets hot to move up the tube, really just a matter of effectiveness. It does a good job in lowering cpu fan noise. Unfortenly the noise of the PSU is very high in these things, or at least my SN41g2, though i belive the P4's have same PSU. The need the same thing on the PSU as the cpu. Also the "heat pipe" is a work of art.
Sure, heat convection flows, but your efficiency goes way up if you have an active flow. Same principle with hot water heating. They used to not have pumps to circulate the water - because it worked - but it's more efficient to have a pump.
...the motherboard manufacturers just don't put the processors on the back side of the motherboards.
Think about it. If the processor and other heat generating chips were on the reverse side you could mount the motherboard in such a way as to press against the large metal backside of your case cabinet. The case cabinet could be designed in such a way as to have indentations that force the processor flat against the case with heat sink gel. In fact the entire case back could be a water-cooled heat sink. This would keep the inside of the case "water-free".
Sure, this would take a radical new case design and motherboard (another industry standard), but that seems to be where we are headed right? I mean processors are getting hotter and Intel and AMD are trying to figure out what to do.
Why not?
BTW, I think it has something to do with the fact that the motherboard components are all wave soldered on one side. This would melt most plastic components on that side. I'm not sure about this.
Nah... I'd use transformer oil, and I don't think a Lipton Cup-a-Soup would taste quite the same.
Transformer oil, however, is probably quite suitable for use in a CPU cooling system.
It has a higher breakdown voltage than air and is almost infinitely less conductive than real-world (ie. impure) water. Transformer oils are specifically designed for use as an insulating material in large power distribution transformers. Electric utility transformers at power substations, operating in the range of hundreds of thousands of volts, would arc between windings if the oil leaked out of them and air - with its lower breakdown voltage - seeped in. (Air breaks down at about 3kV per millimeter.) You can feel pretty confident that leaked oil won't short out IC pins on your motherboard. Hell, you could also ditch your power supply fan and fill that full of oil, too - just beware of relays and other mechanical components.
Heat transfer is a big reason for oil, too. In a car engine, much of the heat is generated by friction in the bearings, and motor oil pumped through the bearings takes that heat away. Transformer oil doesn't have to lubricate, nor does it have to carry away huge amounts of impurities or combustion by-products as in a car engine - the biggest requirements are heat carrying capability and high breakdown voltage. Large pole pigs (pole-mounted power transformers) are usually oil-filled and often have pipes coming from the bottom and going to the top - they serve as radiators. Oil flow is not by pump, the reliability would be too low - they're convective, too.
Finally, viscosity. Yes, this might be difficult, but transformer oils are available in a variety of thicknesses. You want a viscosity corresponding to SAE 0, which is the same as water. Even less might be available, though I've personally never seen it.
Density changes with temperature rise will have to be considered, since the lower density of hot liquids causes them to rise in the system (and is also the physics behind lava lamps). The system that guy designed is based on the density changes of water. Transformer oil won't behave the same way; accordingly, you'll have to whip out the old slide-rule and do some math. Calculus is your friend. Fortunately, the data on transformer oil should be readily available, it's an important design criteria.
Voltesso and Diala are good trade names which I've personally used in transformers loaded to hundreds of kilowatts at over 250,000V, at RF frequencies. (FAA obstruction lights on large VLF radio transmitting towers.) They're ALL PCB-free, and while you don't want to drink it, they're no more toxic than motor oil. And it takes a hell of a lot of work to make them catch fire.
In short, transformer oils are available in a variety of viscosities, are specifically engineered for their thermal transfer capabilities, are not electrically conductive, not dangerous, and are suitable for almost all of your electronic cooling needs.
The only problem I forsee is that you're gonna have a hard time buying them in quantities less than 45-gallon drums... though the drum would make a great passive radiator. Seriously, talk to a couple of linesmen with your local power utility, maybe you'll be able to talk your way into a couple of gallons of it.
And once that's done across all the machines in your compile farm, you can get to work tackling the big problems of why Linux isn't ready for the desktop yet.
Fire and Meat. Yummy.
That was a very informative post, does anyone know if motor oil is conductive, I would think that a quart of 5W20 or another light oil would flow pretty well through a small submersable pump. My favorite transformer oil story was from a local Utility guy who came to our school years ago. He asked us if we ever wanted to shoot the transformers with our pellet guns, and then told us that he used to want to as a kid, but that it would be a bad idea since the oil would leak and the transformer would fail possibly explosivly.
What I found funny was that I don't think a single person had ever thought about shooting a transformer until he mentioned it, and the fact that they could explode might be something that would encourage young boys to shoot one with their pellet gun.
Degaussing scares the bad magnetism out of the monitor and fills it with good karma.
It is about -12 deg outside at the moment. Why do this when I can just put my machine outside my window. You guys in California have to resort to something like this? Time to move....
Got Code?
I guess Intel meant the surface of the Sun. This outer layer (photosphere) has a temperature of 6000C aprox. Yeah, it's damn hot but quite below from the 15000000C of the core (where the nuclear reactions take place).
:-)
Molten lava temperature is ~1000C so only 5000C to go
simple multimeter tests don't just cut it, unless it can measure the 'hit through'(sorry, my english sucks and i don't know the proper word) capabilities of the substance.
water would make a fine insulator unless the 'hit through'(amount of voltage differential needed for the electricity to jump/hit like lighting through something) was small(and no, i'm not an electricity-engineer).
anyways, this kind of cooling has been done(submerging the whole mobo in something), couple of times. one guy used some biograde mineral oil succesfully.
theres at least one no-pump commercial solution too for liquid cooling, but it has a fan on the radiator.
though, in my opinion, getting rid of the pump doesn't bring you anything 'extra' since the pump makes next to zero noise, and noise damping the pump from environment is easy too. the real problem lies in how to get the water to keep cool without having extra fans(heatload on it gets quite big if you have cpu, gfx-card, chipset, psu, hd's and etc watercooled for silence). the bowl of that size that's in the article won't cut it.
and really, k6-2 could be cooled enough with just about any lump of metal compared to the 76w+ modern cpu's.
world was created 5 seconds before this post as it is.
Why not take in one step further and install a CPU-powered lava lamp? It's the next logical step from AOpen's valve amplifier motherboards.
I remember posting in a car forum after doing some research. Oils are very BAD.
.6W/mK (bout halfway down the page) .13W/mK.
Thermal contuctivity for water is
The oil I found was from some company called Slovnaft out of Slovakia (the only one I could find that would provide details). But their oil that is specifically meant for moving heat has a thermal conductivity of
Another thing I might point out is if youve ever got motor oil on your hands youll notice it feels warmer than water of the same temperature. It doesnt carry heat away like water will.
if youve ever got motor oil on your hands youll notice it feels warmer than water of the same temperature. It doesnt carry heat away like water will.
:-)
True, but water is about a zillion times more evaporative than oil, so if you get any water on you, especially if it's warmer than body temp, it's already evaporating and thus feels cooler than warm oil would.
If you have ever got your hands wet in the winter time, you'll notice that it literally sucks the heat right out of your hand because the relative humidity in winter is usually very low and it doesn't take much to make the water on your hands start evaporating. If you got cold oil on your hands (at the same temperature as the cold water) it won't feel nearly as cold as it's not evaporating. It will pull enough heat out of your hands to reach thermal equilibrium and then stop.
If you have ever splashed hot water on yourself, you'll notice that even if you get burned, the inital 'hot' part of it is over with almost immediately. Hot oil on the other continues to feel hot and will continue to burn you much longer.
In an enclosed system where there is no evaporation, the difference won't be nearly as great.
Has anyone ever built a water-cooled PC that uses an external fountain as a radiator? Obviously you would want it far enough away from the PC so as to prevent splashing, but I think one of those little zen rock fountains would make an interesting and relaxing radiator, as long as you remembered to keep adding water...
A computer once beat me at chess, but it was no match for me at kick boxing -- Emo Phillips