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Sandia's Smart Heat Pipe
An anonymous reader writes "Science Blog is reporting a story from Sandia National Laboratory, best known for its nuclear weapons research. "Evacuating heat is one of the great problems facing engineers as they design faster laptops by downsizing circuit sizes and stacking chips one above the other. The heat from more circuits and chips increase the likelihood of circuit failures as well as overly heated laps. "Space, military, and consumer applications, are all bumping up against a thermal barrier," says Sandia researcher Mike Rightley, whose newly patented "smart" heat pipe seems to solve the problem. The simple, self-powered mechanism transfers heat to the side edge of the computer, where air fins or a tiny fan can dissipate the unwanted energy into air."
I see nothing in this article that distinguishes this "smart" heat pipe from standard heat pipes that have existed for quite some time.
Yes, this technology is significantly better than air being blown over a heatsink on a CPU.
No, it's nothing new. Shuttle small-form-factor PCs anyone? And Dell Inspiron 8x00 series laptops too. Probably other laptop manufacturers are also already using heat pipes.
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I remember sitting in on a presentation of heat pipe theory and applications.
The article talks about how the methanol vaporizes at one end, and condenses at the other. Then the liquid wicks back to the first end, where it can be vaporized again. You don't necessarily have to use methanol; the coolant is varied according to the temperature range you operate in.
The pipe pressure is carefully set so that the vaporization takes place at the optimal temperature. Usually these pipes are used in a vertical configuration, so that the vapor rises and gets to the other end more quickly, and the condensate sinks to other end quickly. The heat pipe behavior is then kind of like a passive heat diode.
A use for heat pipes was presented; apparently a lot of structures were sinking on the Alaska pipeline. When the ground was frozen, everything was fine...but the permafrost was receding in the warm months. The solution was to keep the ground frozen all the time, by removing heat from about 20 feet down. Heat pipes were constructed with a vaporization point at the desired temperature, and sunk into the ground at the problem areas. The ground stayed frozen, and the problem was solved.
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For those having trouble with the reference:
phimosis: unretractable foreskin
balanitis: inflammation of the helmet
There's nothing there to absorb the heat...
This isn't a new idea. Technology has come full circle- the first computers were cooled with fluid pumps, and guess what? We were right the first time.
And the old problems with heat pumps will return- leaks that short out the machine, the added complexity of the design, yet another part to get disconnected, and idiots buring themselves by opening the box and touching the thing after it's been running for days.
Heat sinks are just that- sinks. They hold the heat, they don't disperse it. Almost any heat dispersal method is preferable to heat sinks, which is preferable to no thermal control whatsoever.
But they better make those tubes industrial-strength, especially on laptops. Computers are put through a lot rougher treatment than they're ever specced for; the hoses used for this had better be up to the task.
I can see a very real possibility of a computer springing a leak and shorting itself out, and/or dripping on the user and scalding him/her- and that user very well might have reason to sue.
It's a good idea. Just as it was the first time. But engineers need to take this type of thing into account in the original spec; it can't be slapped on at the end like just another Microsoft UI.
Warning: Poster of this comment is a nerd. Just like everybody else here.
If I understand the article correctly, this is new in that is has a very small size, and uses a very small amount of liquid to conduct the heat, and requires no mechanical pump to drive it, no rewiring, etc.
Because of this, it can easily be fit into an existing design with minimal re-engineering of your product. That's where the cost comes into play for manufacturers -- or has no one noticed that we don't see liquid cooling in consumer computers yet? Too expensive to add into existing designs. Also, you get one leak, there goes your computer. Not to mention the potential hazards of having a liquid flowing over live electrical circuits.
Small size, small amount of coolant liquid, and no need to add mechanical pumps. Any laptop manufacturer could add this and not have to increase the price to cover the retooling costs for the manufacturing process. This means a faster -- and naturally hotter -- chip could be put into the laptop. That will mean laptops that are as fast as desktops, instead of lagging behind by a few years.
What's the name of the company that will be making these things? I want to buy stock NOW while I can still afford it!!!!
Whew! This water sure is cold!
One of the largest applications of "heat pipes" is in the Alyeska Pipeline. The oil they're moving is hotter than the permafrost supporting the pipe. If the permafrost melts... well, we can guess what happens.
So if you look at the picture on the site, the heat pipe is actually built into the support structure of the pipe joints. The little vanes on the posts wick away heat that is absorbed from the ground. They use a substance that has a very low vapor pressure in order to capitalize on the energy released in the latent heat of vaporization and condensation of the anhydrous ammonia (caused by the cold Alaska air circling around the vanes). You can find the details of this huge heat-pipe installation on their Web site.
Pretty cool (literally)!
TTFN
See also: Thermos. A layer of vacuum in a silvered container.
The micro grooves layed in the pipe by photolithographic techniques so the medium can wick properly along designed paths is probably what is patented here.
It might be worth it if you could come up with a super-efficient generator, but that's pretty unlikely. Furthermore, the temperature gradients here are pretty low (boiling point of methanol vs. room temp), so there's not a whole lot of ooomph to drive your generator. Heat pipe designers are pretty happy when they can use this thermal gradient just to power their heat pipe convection, actual generation seems a long way off.
It is more innovative over the simple convection that you describe in that the use of a capilliarized wick (inner tube) forces pressure itself to be the media for which the temp is transferred is highly efficient manner.
Hold a heat pipe over a flame with your bare hands at the other end and within two seconds you will be forced to drop it.
Place a heat pipe in ice and likewise you will feel the cold transfer to the other end in a likewise amazingly fast duration.
The middle of the pipe will experience no immediate temp change because no evap/condensation occurs there.
Thus a truly innovative method of efficiently inducing thermal transfer from point a to discretely distant point b.
Existing heat pipes already use capillary action. I remember a while ago looking at info on heat pipes out of curiosity, and I saw a number of descriptions of various wicks that were in use, and this doesn't appear to be anything new, except thay maybe they've made slightly more efficient wicks.
Even these new heat pipes almost surely use a phase change - It's most likely possible to do it without a phase change, but far less effective/efficient. Current heat pipes use a phase change combined with capillary action - Gas vaporizes on heat source, condenses at radiator, and is wicked back. Heat pipes can be made without wicks, but they are orientation-sensitive - i.e. the condenser must be above the evaporator so gravity will bring the condensed medium back to the heat source. The Shuttle may not use a wick since the condenser is higher than the CPU, but in Dell laptops they are even, I'm positive that laptop heatpipes already use wicks.
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Conduction is heat transfer thru direct contact. You touch the stove, it burns your skin.
Convection is the transfer of heat via a moving medium. Air at the earth's surface is warmed by the sun's radiation, causing the air to rise. The heat is then transferred to the surrounding cold air, which causes the previously warm air to sink back down.
Radiation if the transfer of heat via electromagnetic radiation. All objects above absolute zero emit some form of EM radiation in proportion to the fourth power of their absolute temperature. Also involved is a coefficient that depends on how close a radiator is to an ideal 'black body' - ie a perfect radiator. See Stefan-Boltzmann equation Inet = e*s*A(T^4 - T0^4) where Inet is the net power radiated in Watts, e is the emissivity coefficient, s is Stefan's constant = 5.6703 x 10-8 W/m^2 K^4, A is the area, and T is the absolute temp and T0 is the ambient temp. (To get the total radiation emitted, set T0 = 0). The peak wavelength of the radiation is given by Wein's displacement law, lambda = 2.898 mm * K / T, where the 2.898 mm * K is a universal constant and T is the absolute temp of the object.
For example, a person has about 1.4m^2 of skin at 33C = 306K. If you assume they're a perfect radiator, in a room at 20C the person is emitting 111W of power, net. The emission peak wavelength is approx 9.5 um, which is in the part of the EM spectrum called "infrared".
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Zero-g is also a factor. Lovell actually commented in his debriefing that you could get warmer if you didn't move. A small blanket of warm air would form around you, and since there was not much to move it around (all the fans being shut off) it would just stay there. Then you'd move and you'd be freezing again.
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bringing less warmth to your extremeties. which also means less heat loss through your extremities; your hands and feet will get colder but you get less degradation of your core temperature. Put on gloves, a hat and drink hot coffee instead of soda and you'll be fine.
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It is also different in that they are using a phase-change heat transfer. When most heat pipes boil the water they are completely ineffective.
Also, traditional heat pipes rely on elevation differences to maintain flow.
If it was a heat pipe, it was probably not solid copper, though it looked like it. It would be a copper tube filled with a volatile liquid. Liquid evaporates at the hot end, diffuses to cool end where it condenses, transferring heat as it does so. But most of them looked solid.
This invention just looks (from the uninformative article) as if they hae some improvements on the mechanical structire and on helping the methanol get thr right idea about where to flow (cappillaries with "one way" structires, I would guess).
As said elsewhere, only incremental. But then, the latest Pentium is "only incremental" on the original 386 - but thos increments have taken us a long way.
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Thermocouples has very low thermal efficiencies due to heat conductance across the pad and heat generated from the electrical resistance.
When you have a 200 watt power supply driving the thing that isn't a problem. For a laptop it would exhaust the batteries pretty quickly.
As I mentioned in another post, phase-change heat transfer in heat pipes is old hat. So is using a wick to allow for the heat pipe to work without an elevation difference. For an example of the latter, see the aforementioned Dell Inspiron 8200. Has no problem working with the laptop level, or even with the laptop tilted backwards (i.e. evaporator above condenser)
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