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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."
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.
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?
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."
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.