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."

Comments

Had a presentation of this once

[cybermace5]

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.

Re:The real meaning of "memory leak"

[cybermace5]

There really isn't much liquid in these. If you shook one, I doubt you'd even hear a slosh. The heat pipes work by adjusting the pressure in the pipe so that the methanol is teetering between liquid and vapor state. So technically the heat pipe moves methanol "steam", and the liquid at any time is measured in droplets.

They work most efficiently in a vertical configuration (warm vapor rises, cool droplets fall), so Sandia's work is very useful: they are developing more efficient ways to transfer the liquid back to the hotspot in a horizontal configuration, via capillary action instead of gravity.

Alyeska Pipeline is a very large heat pipe user

[gregger]

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

Re:Other uses for heat

[Jeremiah Blatz]

UCRowerG writes:
I wonder what else designers could do with that extra heat energy. If these heat pipes turn methanol into vapor, carry it to heat fans, then recondense it (due to heat loss) back into liquid.... isn't this process quite similar to how turbines work with steam? I wonder how much power could be gleaned from the extra heat. Maybe someone could design a tiny electrical generator. I doubt you could run anything significant off the power output, but I'm sure there could be some use for it, rather than simply letting that extra energy go to waste.

The problem with solutions like this is that the power generation step interferes with the cooling step. In other words, the inefficiency in the power generation reduces the efficiency of the cooling. However, the whole point of this is cooling, which means that you have to put in bigger, heavier cooling mechanisms to cope with the reduced efficiency.

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.

Capillary action

[Andy Dodd]

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.