MMaterialsgateNEWS 2012/06/28

Related MaterialsgateCARDS

Energy: Better surfaces could help dissipate heat

Heat transfer in everything from computer chips to powerplants could be improved through new analysis of surface textures.

Cooling systems that use a liquid that changes phase — such as water boiling on a surface — can play an important part in many developing technologies, including advanced microchips and concentrated solar-power systems. But understanding exactly how such systems work, and what kinds of surfaces maximize the transfer of heat, has remained a challenging problem.

Now, researchers at MIT have found that relatively simple, microscale roughening of a surface can dramatically enhance its transfer of heat. Such an approach could be far less complex and more durable than approaches that enhance heat transfer through smaller patterning in the nanometer (billionths of a meter) range. The new research also provides a theoretical framework for analyzing the behavior of such systems, pointing the way to even greater improvements.

The work was published this month in the journal Applied Physics Letters, in a paper co-authored by graduate student Kuang-Han Chu, postdoc Ryan Enright and Evelyn Wang, an associate professor of mechanical engineering.

“Heat dissipation is a major problem” in many fields, especially electronics, Wang says; the use of phase-change liquids such as boiling water to transfer heat away from a surface “has been an area of significant interest for many decades.” But until now, there has not been a good understanding of parameters that determine how different materials — and especially surface texturing — might affect heat-transfer performance. “Because of the complexities of the phase-change process, it’s only recently that we have an ability to manipulate” surfaces to optimize the process, Wang says, thanks to advances in micro- and nanotechnology.

Chu says a major potential application is in server farms, where the need to keep many processors cool contributes significantly to energy costs. While this research analyzed the use of water for cooling, he adds that the team “believe[s] this research is generalizable, no matter what the fluid.”

The team concluded that the reason surface roughness greatly enhances heat transfer — more than doubling the maximum heat dissipation — is that it enhances capillary action at the surface, helping keep a line of vapor bubbles “pinned” to the heat transfer surface, delaying the formation of a vapor layer that greatly reduces cooling.

To test the process, the researchers made a series of postage-stamp-sized silicon wafers with varying degrees of surface roughness, including some perfectly smooth samples for comparison. The degree of roughness is measured as the portion of the surface area that can come into contact with a liquid, as compared to a completely smooth surface. (For example, if you crumpled a piece of paper and then flattened it back out so that it covered an area half as large as the original sheet, that would represent a roughness of 2.)

The researchers found that systematically increasing roughness led to a proportional increase in heat-dissipation capability, regardless of the dimensions of the surface-roughening features. The results showed that a simple roughening of the surface improved heat transfer as much as the best previous techniques studied, which used a much more complex process to produce nanoscale patterns on the surface.

In addition to the experimental work, the team developed an analytical model that very precisely matches the observed results. Researchers can now use that model to optimize surfaces for particular applications.

“There has been limited understanding of what kind of structures you need” for effective heat transfer, Wang says. This new research “serves as an important first step” toward such analysis.

It turns out heat-transfer is almost entirely a function of a surface’s overall roughness, Wang says, and is based on the balance between various forces acting on the vapor bubbles that serve to dissipate heat: surface tension, momentum and buoyancy .

While the most immediate applications would likely be in high-performance electronic devices, and perhaps in concentrated solar-power systems, the same principles could apply to larger systems such as powerplant boilers, desalination plants or nuclear reactors, the researchers say.

Satish Kandlikar, a professor of mechanical engineering at the Rochester Institute of Technology who was not involved in this work, says it is “quite remarkable to achieve heat fluxes” as great as these “on silicon surfaces without complex micro- or nanofabrication process steps. This development opens doors to a new class of surface structures combining micro- and nanoscale features.” He adds that the MIT team “should be complimented for this major research finding. It will provide new directions especially in chip-cooling applications.”

The work was supported by the Battelle Memorial Institute and the Air Force Office of Scientific Research. The team received help in fabrication from the MIT Microsystems Technology Lab.

Source: Massachusetts Institute of Technology – 26.06.2012.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

Researchers from North Carolina State University have found a way to create much slimmer thin-film solar cells without sacrificing the cells’ ability to absorb solar energy. Making the cells thinner should significantly decrease manufacturing costs for the technology.

“We were able to create solar cells using a ‘nanoscale sandwich’ design with an ultra-thin ‘active’ layer,” says Dr. Linyou Cao, an assistant professor of materials science and engineering at NC State and co-author of a paper describing the research. “For example, we created a solar cell with an active layer of amorphous silicon that is only 70 nanometers (nm) thick. This is a significant improvement, because typical thin-film solar cells currently on the market that also use amorphous silicon have active layers between 300 and 500 nm thick.” The “active” layer in thin-film solar cells is the layer of material that actually absorbs solar energy for conversion into electricity... more read more

New catalyst dramatically cheaper without sacrificing performance

Engineers at the University of Wisconsin-Milwaukee (UWM) have identified a catalyst that provides the same level of efficiency in microbial fuel cells (MFCs) as the currently used platinum catalyst, but at 5% of the cost. Since more than 60% of the investment in making microbial fuel cells is the cost of platinum, the discovery may lead to much more affordable energy conversion and storage devices. The material – nitrogen-enriched iron-carbon nanorods – also has the potential to replace the platinum catalyst used in hydrogen-producing microbial electrolysis cells (MECs), which use organic matter to generate a possible alternative to fossil fuels. "Fuel cells are capable of directly... more read more

A team of physicists from the University of Miami introduces a breakthrough in the understanding of high-temperature superconductivity

Researchers from the University of Miami (UM) are unveiling a novel theory for high-temperature superconductivity. The team hopes the new finding gives insight into the process, and brings the scientific community closer to achieving superconductivity at higher temperatures than currently possible. This is a breakthrough that could transform our world. Superconductors are composed of specific metals or mixtures of metals that at very low temperatures allow a current to flow without resistance. They are used in everything from electric devices, to medical imaging machines, to wireless communications. Although they have a wide range of applications, the possibilities are limited by temperature... more read more

A new type of durable, environmentally-benign blue pigment discovered at Oregon State University has also been found to have unusual characteristics in reflecting heat – it’s a “cool blue” compound that could become important in new approaches to saving energy in buildings.

The compound, which has now received patent approval, was discovered about three years ago almost by chance, as OSU scientists were studying some materials for their electrical properties. Its potential use to help reduce heat absorption on the roofs and walls of buildings – which is an evolving field of considerable interest in warm regions where cooling is a major expense – adds another role for the material, which is now being considered for various commercial applications. “This pigment has infrared heat reflectivity of about 40 percent, which is significantly higher than most blue pigments now being used,” said Mas Subramanian, an OSU professor of chemistry who discovered... more read more


Partner of the Week

Search in MaterialsgateNEWS

Books and products