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Tiny Bubbles Key to Cooling Crazy Hot CPUs
Smaz writes "With future CPUs expected to generate as much as four times the heat of today's processors, wicking away that heat remains one of the biggest engineering hurdles in the biz. Researchers at Purdue have developed a pumpless liquid-cooling system that removes nearly six times more heat than existing systems. The trick, it seems, is in the tiny bubbles. From the Science Blog."
From the Purdue University:
Tiny bubbles are key to liquid-cooled system for future computers
WEST LAFAYETTE, Ind. - Purdue University researchers have made a discovery that may lead to the development of an innovative liquid-cooling system for future computer chips, which are expected to generate four times more heat than today's chips.
Researchers had thought that bubbles might block the circulation of liquid forced to flow through "microchannels" only three times the width of a human hair. Engineers also thought that small electric pumps might be needed to push liquid through the narrow channels, increasing the cost and complexity while decreasing the reliability of new cooling systems for computers.
Purdue researchers, however, have solved both of these potential engineering hurdles, developing a "pumpless" liquid- cooling system that removes nearly six times more heat than existing miniature pumpless liquid-cooling systems, said Issam Mudawar, a professor of mechanical engineering.
Liquid forced through microchannels forms smaller bubbles than expected, Mudawar said he was surprised to learn. Moreover, decreasing the diameter of the microchannels increased the cooling efficiency of the system by causing the liquid to form even smaller bubbles, which is contrary to the expected result.
Because the bubbles are much smaller than the diameter of the microchannels, they flow easily through the channels. The Purdue-developed system does not require a pump because the liquid circulates in a self-sustaining flow in a closed loop that carries heat away from a computer chip.
Findings about the new cooling system are detailed in a research paper appearing in the March issue of IEEE Transactions on Components and Packaging Technologies, published by the Institute of Electrical and Electronics Engineers. The paper was written by Mudawar and graduate student Swaraj Mukherjee.
Innovative cooling systems will be needed in about three years for personal computers expected to contain microprocessor chips that will generate four times more heat than chips in current computers. Whereas current high- performance chips generate about 75 watts per square centimeter, chips in the near future will generate more than 300 watts per square centimeter, Mudawar said.
"Any time you squeeze more circuitry into the same space, you are producing more heat per unit area and per unit volume," he said.
Today's computers use fans and heat sinks containing fins to help cool circuitry. But this technology will not be efficient enough to remove the increasing heat generated by future chips, Mudawar said.
His research team created a liquid-cooling system that uses a closed loop of two vertical, parallel tubes containing a dielectric liquid - or a liquid that does not conduct electricity. The liquid flows through microchannels in a metal plate that is touching the chip. As liquid flows through the channels, it is heated by the chip and begins to boil, producing bubbles of vapor. Because the buoyant vapor bubbles are lighter than the liquid, they rise to the top of the tube, where they are cooled by a fan and condensed back into a liquid. The cool liquid then flows into the parallel tube and descends, creating a self-sustaining flow that eventually re-enters the microchannel plate and starts all over again.
"We were surprised to see that the dielectric liquid forms really miniature bubbles, so they slip through really fast," Mudawar said. "The bubbles don't block the flow, as you would expect."
The researchers found that the system was 5.7 times better at removing heat than existing miniature pumpless liquid- cooling systems.
"This is only a starting point, and much better performance might be possible," Mudawar said.
Future research will focus on testing various designs to see which configurations work best.
"Now that we have a system that we know will work, we are going to test different geometries that will be beneficial to indust
The researchers found that the system was 5.7 times better at removing heat than existing miniature pumpless liquid-cooling systems.
It's misleading to generalize "existing miniature pumpless liquid-cooling systems" to "existing systems", as was done in the discussion header. At least, it made me think article was about a cooling solution six times better than *ALL* existing cooling systems. Of course, this leads one to question how good "existing miniature pumpless liquid-cooling systems" are...
Cavitation has nothing to do with vibration. The sudden changes in pressure in the liquid deform or destroy the material. I've seen better links, but try this article for more information about the complexities in measuring and predicting cavitation caused by bubbles.
Yes but will they keep you from burning your unit ?
No, they'll help it happen faster... No slow heat up of the bottom of the laptop - This heat pump is up to 6 times as efficient as the heat pipe. It'll just get the heat away from the cpu faster, no help in keeping it away from your unit.
To recap - No nude laptopping. It is not allowed.
Just because I doubt myself does not mean I find your position compelling.
Here's a good analysis on the current state of CPU heat, for those of us who need to be brought up-to-date on the subject to understand the benefits of the new technology...
Why do I h8 apple?
It's the same principle used in cooling nuclear reactors - deals with the Laminar Flow layer in fluids. Pretty simple actually. The surface area of the bubbles (must be small or they begin to restrict the flow) is much larger than the surface area of the overall fluid. Sounds weird, but it's true.
The benefit of "tiny bubbles" is the bubbles or transfering latent heat of vaporization into the channel (the energy required to boil the fluid), these bubbles also cause mixing of the fluid in the channel.
Two terms to look up if your interested in this aspect of Heat Transfer and Fluid Flow would be subnucleate boiling and the departure from it. There is a balance between the amount of boiling and the amount of heat transfer. Not enough and you don't get many benifits... too much and the large bubbles that form on the channel walls effectively create a steam void that has a much higher specific heat then the fluid used for cooling... basically it is acting as an insulator preventing heat transfer into the fluid in the channel... a very bad thing [tm]. That is where departure from nucleate boiling comes in (this being the good thing) departure being where it starts getting bad very quickly.
Think pot of water for spaghetti before the water really starts boiling... Oh, and I apologize for my horendous spelling but you don't have to spell to run a nuclear reactor.
For those who don't bother to read the article, here's a picture of the thing.
have you been defaced today?
You forgot the addition of plugin.display_plugin_downloader_dialog and setting it to false under about:config
The article is here but unfortunatly it's pay per wiew.
The article also mentioned that future (within 2005) CPU's will generate five to ten times more heat.
The feedback mechanism inside this inkjet head included a sensor so the squirt can be directed to the hottest areas. Really cool. No phun intended.
Melius mori in libertate quam vivere in servitute.
Your explanation of microjets is good.
The parent post makes the mistake of identifying bubble formation with the cavitation damage, where as you point out, it is the bubble collapse that is the dangerous part.
Another important thing to note is that bubble collapse is more of a problem when there is a large disparity between the bubble pressure and the ambient liquid pressure. Lots of liquids, like beer, sustain CO_2 bubbles nicely for lengths of time, without the beer glasses sustaining lots of chipping damage from microjets. The pressure of the gases in beer bubbles can be higher than atmospheric pressure.
Under the ocean, however, where props rotate at high speed, the bubbles that are created have little more than water vapor in them (that's what cavitation is all about - causing the water pressure to drop below its vapor pressure). Those bubbles are highly unstable and short-lived.
"Provided by the management for your protection."
From looking at the article, I don't think that there is any cavitation in these pumps.
Galium Arsenide is the material of the future, and always will be.
The current emphasis on low power CPU's isn't an effort to reverse the power consumption trend, merely to slow it down. In most cases, power consumption offsets performance. Historically, designers have almost always favored performance, resulting in power consumption varying roughly with clock speed (P~af^2) squared for the same family of chip. Current efforts are to bring that closer to a linear relationship (P~af). However, even in this "ideal" relationship, faster chips will use more power (and while you're right about a general shift in priorities, don't kid yourself for a minute that the market will altogether stop demanding faster CPUs anytime soon). While it is technically feasible to make a faster chip use less power (provided the original chip is reasonably inefficient), it is extremely difficult and costly (TTM, R&D efforts, material cost, chip size, etc.).
A second issue is miniturization, since the issue we are concerned about here is not necessarily power consumption, but temperature. Even if we assume that power consumption will stay the same, if we make the chip with half the surface area, then the power dissipation per unit area (roughly proportional to temperature) will double. Thus, even without increasing the power consumption, we run into issues that can only be addressed by advanced cooling systems such as this.
scot
Common perhaps, but correct, no. Guiness bubbles do not defy gravity. To quote - "The reason for this optical illusion is the turbulence in the glass after pouring the drink. Dark liquid is flowing down the inside of the glass and rising in the centre giving us this circulation of fluid. It is this dark fluid rippling down the inside of the glass, superimposed on the white froth, that gives the impression that the bubbles are sinking. Look closely and you'll see what I mean. New Scientist have looked into this question and the fluid dynamics of a pint of Guinness are pretty complicated and it is still impossible to predict the movement of the bubbles by theory. If you want to read more about what is going on in your pint have a look at Pure Genius, pages 56-57 of the 1998 Christmas Special of New Scientist, dated 16/29 December 1998 - 2 January 1999" But yes, I was aware of the attempted humour in your post.
[UID-HeinzIntel]
In laymans terms...
Cooling ability of water alone is good.
Cooling ability of water with slight boiling is really good.
Cooling ability of steam is really bad (3 Mile Island comes to mind among other things).
Very fine line...
The trick is controlling the amount of boiling so that the steam collapses when it is stripped away from pipe surface.
If not.. I hope they have analyzed for the hot channel effect or even worse, flow reversal!!
I too was in nuclear power, and can't spell either
Bad boys rape our young girls but Violet gives willingly.
Do you want a zillion computers needing special disposal? Technowaste is a big-enough problem as it is today, lets not RE-introduce a hazardous material that needs to be handled at EOL.
Actually i know of one right now. Hush Technologies This case is designed for the Via ITX style motherboards, at least its a start. Myself i'm looking forward to getting one.
Being called a dork on Slashdot must be like being called the retard in special ed.