Engineers at Purdue University have replaced the conventional evaporators used in our refrigerators, which can be one meter long over a large area, by "micro-channel heat sinks" which are just over a square inch. According to this news release, their devices can be attached to household fridges, but also to electronic components in military lasers, microwave radar and weapons systems. In fact, as future combat vehicles are expected to generate waste heat densities approaching 1,000 watts per square centimeter, new technologies like this one are necessary to dissipate these heat loads. And the same is true with the chips in your computers, even if the recent battle between AMD and Intel shows that chipmakers are increasingly paying attention to the heat generated by their microprocessors. So who will be the first to benefit from this new cooling technology, the military, your fridge or your computer? Read more.
First, here is a description of the problem.
Electronics for new weapons systems, as well as chips in future computers, will generate five to 10 times more heat than chips in conventional electronic products, requiring better cooling systems. Computers and other electronic equipment are typically cooled with bulky assemblies that use metal fins to dissipate heat and fans to circulate the hot air away from components. But electronic components in new weapons systems, such as advanced lasers and chips in future computers, will generate too much heat to be cooled with conventional systems that use fans, said Issam Mudawar, a professor of mechanical engineering who is leading the research.
So how did they solve this problem?
One possible solution is a "two-phase" cooling system – the same basic technology used in a conventional refrigerator -- in which a liquid coolant absorbs heat, turns into a vapor and is then pressurized by a compressor and condensed back into a liquid to begin the cycle over again.
In work funded by the U. S. Office of Naval Research, Mudawar's team has successfully incorporated the micro-channel heat sink into an ordinary refrigerator. The device, which was attached to a heating element that simulates a hot electronic component, has been tested with a refrigerant called R134a, which is used in household air conditioners and refrigerators.
Now, let's go to some details about the technology which was developed at the Boiling and Two-Phase Flow Laboratory at Purdue University.
Genius is present in every age, but the men carrying it within them remain benumbed unless extraordinary events occur to heat up and melt the mass so that it flows forth.
—Denis Diderot (1713–1784)
The micro-channel heat sink is a copper plate containing numerous grooves 231 microns wide -- or about three times as wide as a human hair -- and 713 microns deep. The tubes in conventional air conditioner evaporators have diameters measured in millimeters or centimeters, depending on the size of the unit, meaning the conventional tubes are several times larger than the micro-channels.
"This is really pushing the envelope in how small you can go with these channels and still have a working device," Mudawar said. "But there is another issue. In conventional systems, the evaporator is actually a very long tube that is wound around many times. So the tube might be a meter in length or more. In the micro-channel heat sink, we are doing everything in 1 inch square."
The news release doesn't give any details about when the technology will be available, but it looks pretty sure that the military forces will use it before you.
For more information, the research work has been published in two parts by the International Journal of Heat and Mass Transfer in its February 2005 issue (Volume 48, Issue 5, Pages 928-940 and 941-955) under the common title "Two-phase flow in high-heat-flux micro-channel heat sink for refrigeration cooling applications."
Here are the links to the abstracts of the two parts of the paper, which are respectively focused on pressure drop characteristics and heat transfer characteristics.
If you don't find the journal in your library, you can purchase the individual articles for $30 each. And that's almost a bargain. The annual subscription fee for this journal is US$5,360!
Sources: Purdue University news release, April 13, 2005; and various websites
Coal is a portable climate. It carries the heat of the tropics to Labrador and the polar circle; and it is the means of transporting itself whithersoever it is wanted. Watt and Stephenson whispered in the ear of mankind their secret, that a half-ounce of coal will draw two tons a mile, and coal carries coal, by rail and by boat, to make Canada as warm as Calcutta, and with its comfort brings its industrial power.
—Ralph Waldo Emerson (1803–1882)
Related stories can be found in the following categories.
Chips
Engineering
Military Applications
Technology.