Archive for Thermal management
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You are browsing the archives of Thermal management.
Background image: Molten glass. Credit: Michael Germann; Dreamstime.com.
Peter and I thought it would be fun to share our five favorite posts from 2012. Finding that choosing only five was nigh impossible, I decided to sort my picks into three categories, which instantly grew my budget to 15 stories!
Advances in science and engineering are subject to forces beyond physics, chemistry, and mathematics, such as politics, culture, history, and more.
USPTO issues flurry of new rules to implement ‘America Invents Act’
Archaic US patent rules were thrown out with adoption of the Leahy-Smith America Invents Act. New rules, though, mean changes in the strategy of innovation.
Data drives engineering of ceramics; workshop asks ‘how well?’
Computational approaches to materials engineering are only as good as the data they consume and digest. A DOD-sponsored workshop evaluated the state-of-affairs for electronic access to ceramic property data and the attendant challenges and opportunities.
Science research drives economic growth, but it’s expensive and slow
What role should governments take in investing in basic research, and how does a nation’s R&D investment impact GDP? There is nothing like an election year—in the US and abroad—to draw attention to what governments should spend money on versus what they do spend money on.
Video: Grand challenges in ceramic science—Preliminary findings from workshop
Researchers go bravely where others cannot or dare not. A group of the nation’s top ceramic science researchers convened to tease out the largest scientific challenges that can be addressed with ceramic materials.
Historic January 1987: YBCO superconductors discovered and Super Bowl XXI
This story about the discovery of high-temperature YBCO superconductors shows that research breakthroughs are often the progeny of systematic, well-executed fundamental research… and serendipity.
I’m an unabashed materials geek, and these were some of my favorite super-sciency stories—with the qualification that I mostly write about science that intrigues me, so this is a lot like choosing a favorite child.
Understanding the ‘between’ spaces: Interfacial phases and solid-state sintering
The formation and stability of interfacial phases in the solid state drives properties, so understanding how interfaces form and the thermodynamics driving them is of paramount importance.
Mullite-like mixed oxides may replace platinum for catalyzing diesel pollution
Manganese-oxide compounds with the mullite crystal structure may one day displace platinum as the catalyst agent in automobile catalytic converters.
High-alumina optical fibers get around Brillouin scattering limitations
Ever wonder how data gets to your smart phone or laptop so fast? A group of glass scientists is working on the next generation on optical fibers that will move more data, faster, and with more accuracy.
High critical current density doped pnictide superconductors
Harnessing the promise of high-temperature superconductivity requires a deep understanding of the physics of magnetism and the influences of composition and microstructure. Plus, what’s not to love about the word “pnictide?”
Heat transfer—two new studies look at effects of interface bonding, surface roughness
The digital age is generating some very sophisticated heat transfer challenges. How exactly does heat egress from a surface, and how can the mechanism be engineered?
Useful metrics for comparing new energy storage technologies
Measuring is an essential experimental activity. However, scientists and engineers must continually ask themselves the question, “Am I measuring something meaningful and useful?”
And this last group of five was just fun to write about.
Don’t wait in line for coffee: How to know where the business opportunity is
A reflection on business, opportunity, finding the way, and waiting in line.
Oldest known pottery dates back 20,000 years and may have changed the course of human history
The earliest ceramic engineers designed pots for cooking and brewing, proof that since time immemorial, engineers bring the life of the party. Literally.
Friday fun video—Gravity-defying Slinky
Adulthood does not mean toys become irrelevant. This video shows that scientists never stop learning the lessons that educational toys can teach.
Technical ceramics and art ceramics—only a brain apart
In the world of ceramics, is there a line between art and science? Yes, sort of—and no, not really. The American Ceramic Society serves the professional needs of engineers, scientists, studio artists, and hobbyists.
A castle vacation, poster session included
An October vacation to Germany included a conference at a Bavarian castle and the opportunity to talk shop with some of the best minds in the world working on biomineralization.
Were you counting? Me neither. Did you have a favorite story or topic that we covered? Let us know!
Best wishes for a Happy New Year!
A lot of engineering revolves around pumping it in to make a reaction happen, like glass melting, for example. A lot of engineering revolves around sucking it out, like quenching, for example. Plenty of engineers make good livings managing heat.
But, for all the time and effort given to heat transfer and thermal management, how much is really known about the mechanics of how heat transfers?
Two new papers look at heat transfer from different perspectives—interfaces and surfaces—and provide some interesting insights.
A team at the University of Illinois at Urbana-Champaign studied the atomic-scale mechanism of heat transfer between two interfacing surfaces. Interfaces between materials disrupt heat flow, so understanding the nature of heat transfer at interfaces is important, for example, for coatings and bonded joints.
Heat propagates via phonons, which are lattice vibrations that move in a wavelike fashion through the material. But, the mechanism by which this happens is not well understood, and thus, neither are the factors that influence it. David Cahill, UIUC materials science professor and coauthor of the paper, says in a press release, “Compared to our knowledge of how electricity and light travel through materials, scientists’ knowledge of heat flow is rather rudimentary.”
Part of the reason is that accurately measuring temperatures at very small time and length scales has been very difficult. Cahill’s group has developed a technique for studying heat flow using laser pulses of a trillionth of a second with nanometer-depth resolution. Cahill’s group teamed up with UIUC MSE professor, Paul Braun, to study how atomic-scale features affect heat transport.
Using a quartz substrate, the team created a “molecular sandwich” comprising the quartz, a self-assembled monolayer and a very thin topping of gold. The gold layer was zapped with a heat pulse and they measured how the heat travelled through the SAM to the quartz. The effect of bond strength on heat transfer was studied by modifying the SAM layer’s end group chemistry and, therefore, its bond strength with the gold layer.
The key, they found, was the strength of the bond between the SAM layer and the gold layer. Stronger bonds led to more heat flow, up to twice as much. Specifically, SAM-gold interfaces with van der Waals bonds were twice as resistant to heat as covalently bonded interfaces.
“We’ve basically shown that changing even a single layer of atoms at the interface between two materials significantly impacts heat flow across that interface,” says Mark Losego in the release. Losego is lead author of the paper, which is based on his postdoctoral work. He is now a research professor at North Carolina State University. He says, too, “If the vibrational modes for the two solids were more similar, we could expect changes of up to a factor of 10 or more.”
That, is, the interface can be engineered for heat transfer efficiency. They verified that this could be done by “dialing in” a heat flow value by systematically adjusting the SAM-gold interface chemistry.
This work is consistent with some of the ideas batted around last spring at the Grand Challenges in Ceramic Science workshop, where several of the grand challenges identified are based on new abilities to control, engineer and characterize interfaces and their properties.
The UIUC paper is “Effects of chemical bonding on heat transport across interfaces,” Nature Materials (doi : 10.1038/nmat3303)
An MIT group also just published a paper on heat transfer, but their focus was on how surface roughness influenced heat transfer in cooling systems based on liquids that change phases, for example, water boiling on a surface.
In an elegantly simple experiment, the researchers found that microscale texturing of a surface can dramatically increase the heat transfer and that, according to the press release, “increasing roughness led to a proportional increase in heat-dissipation capability, regardless of the dimensions of the surface-roughening features.” The study found that heat dissipation could be more than doubled by roughening the surface.
The team, led by Evelyn Wang, associate professor of mechanical engineering, explains in the paper that surface roughness enhances the capillary action at the surface, which keeps a layer of vapor bubbles “pinned” to the heat transfer surface. Because the vapor bubbles are pinned, the formation of a vapor layer around the surface, which has an insulating effect that suppresses cooling, is delayed.
The MIT work could improve the heat management of systems like server farms, concentrating solar power plants, desalination plants or other large systems that depend on liquid phase change cooling systems.
The MIT paper is “Structured surfaces for enhanced pool boiling heat transfer,” Applied Physics Letters (doi:10.1063/1.4724190).