Showing posts with label cooling. Show all posts
Showing posts with label cooling. Show all posts

Friday, September 9, 2011

Cooling down global warming

Carbon capture has long been identified as a critical technology needed to prevent global warming, but efficient and economical ways to do it have been hard to find.


A new process to capture and convert , discovered by a chemist in the College of Liberal Arts and Sciences, has just been awarded a patent. It uses cheap catalysts, , and heat to convert CO2 and water into useful chemicals or fuels.


Steve Suib, Board of Trustees Distinguished Professor of and the 2011 Connecticut Medal of Science winner, found a way to use , such as and zinc oxides, as catalysts in a conversion process that also uses heat and electricity.


The newly patented method can be run as a continuous, rather than a batch, process, to yield large amounts of a product. What is made depends on the catalyst used. Potential products include paraformaldehyde, used in and in processes in industry, or , the largest bulk chemical in the world, used in products such as milk bottles.


The process could also be used to generate and a variety of hydrocarbons.


“You can make a significant amount of material at high conversions over a long period of time,” Suib says.


CO2 and H2O are abundant but hard to activate in a chemical process, Suib points out: “It is difficult because both of those molecules are relatively stable.”


The process was developed in Suib’s lab, and Ph.D. candidate Boxun Hu, soon to graduate, was heavily involved in the work, which will be published, Suib says.


The patent was granted in late June. It improves on an earlier process that Suib patented in 2009, which used a more expensive —platinum—and produced little product. The earlier process was the subject of a 2010 paper in the journal Applied Catalysis Part A.


Both patents are jointly held by UConn, through the Office of Technology Commercialization, and Catelectric Advanced Electrocatalysis, a company that began as part of UConn’s Technology Incubation Program. Catelectric specializes in improved catalysis processes.


Suib has received research grants from Catelectric to work on the process. He has also had extensive Department of Energy grant funding, and is the lead researcher on a $1.8 million DoE grant to make catalysts for a pilot biomass conversion plant that will be built at UConn.


Suib’s latest patent—he has about 50—is a combined process and composition of matter patent. While process patents can be hard to enforce, Suib says—it is difficult to tell whether a possible infringer is varying or using the same process—the composition of matter component of the patent makes infringement easier to pinpoint.


If the newly patented process is used, UConn would get royalties from the use.


The next step would be to take what is a rather crude, laboratory process and scale it up to the pilot plant stage for testing, and eventually to the manufacturing stage, Suib says.


The costs of heat and electricity used in the process would then be considerations. Electricity costs are high in Connecticut compared with other states, Suib notes. The technology of capturing heat, and even excess CO2, from existing manufacturing plants might be considered, allowing factories to use their excess heat in a process that would result in making new chemicals.


The “Buck Rogers” idea now being floated is to capture heat escaping from nuclear power plants and use that as a heat source, he says.


The effort to capture and convert CO2 into useful products, mitigating in the process, is one that has captured his interest: “A lot of people say, ‘you just can’t do this’—but those are the problems that are interesting.”


Provided by University of Connecticut (news : web)

Saturday, March 12, 2011

Silver-diamond composite offers cooling capabilities for electronics

Silver-diamond composite offers cooling capabilities for electronics

Enlarge

A microscope image of diamond particles. (Credit: Jason Nadler)

(PhysOrg.com) -- Researchers at the Georgia Tech Research Institute (GTRI) are developing a solid composite material to help cool small, powerful microelectronics used in defense systems. The material, composed of silver and diamond, promises an exceptional degree of thermal conductivity compared to materials currently used for this application.


The research is focused on producing a silver-diamond thermal shim of unprecedented thinness – 250 microns or less. The ratio of silver to diamond in the material can be tailored to allow the shim to be bonded with low thermal-expansion stress to the high-power wide-bandgap semiconductors planned for next generation phased-array radars.


Thermal shims are needed to pull heat from these high-power semiconductors and transfer it to heat-dissipating devices such as fins, fans or heat pipes. Since the semiconductors work in very confined operating spaces, it is necessary that the shims be made from a material that packs high into a tiny structure.


Diamonds provide the bulk of thermal conductivity, while silver suspends the diamond particles within the composite and contributes to high thermal conductivity that is 25 percent better than copper. To date, tests indicate that the silver-diamond composite performs extremely well in two key areas -- thermal conductivity and thermal expansion.


'We have already observed clear performance benefits -- an estimated temperature decrease from 285 degrees Celsius to 181 degrees Celsius -- using a material of 50 percent diamond in a 250-micron shim,' said Jason Nadler, a GTRI research engineer who is leading the project.


The researchers are approaching diamond percentages that can be as high as 85 percent, in a shim less than 250 microns in thickness. These increased percentages of diamond are yielding even better performance results in prototype testing.


Nadler added that this novel approach to silver-diamond composites holds definite technology-transfer promise. No material currently available offers this combination of performance and thinness.


Natural Thermal Conductors


Diamond is the most thermally conductive natural material, with a rating of approximately 2,000 watts per meter Kelvin, which is a measure of thermal efficiency. Silver, which is among the most thermally conductive metals, has a significantly lower rating -- 400 watts per meter K.


Nadler explained that adding silver is necessary to:


- bond the loose diamond particles into a stable matrix;
- allow precise cutting of the material to form components of exact sizes;
- match thermal expansion to that of the semiconductor device being cooled;
- create a more thermally effective interface between the diamonds.


Nadler and his team use diamond particles, resembling grains of sand, that can be molded into a planar form.


The problem is, a sand-like material doesn't hold together well. A matrix of silver -- soft, ductile and sticky -- is needed to keep the diamond particles together and achieve a robust .


Silver-diamond composite offers cooling capabilities for electronics
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This image shows different preparations of diamonds, ready for integration into a silver matrix. (Credit: Gary Meek)

In addition, because the malleable silver matrix completely surrounds the diamond particles, it supports cutting the composite to the precise dimensions needed to form components like thermal shims. And silver allows those components to bond readily to other surfaces, such as semiconductors.

Tailoring Thermal Expansion


As any material heats up, it expands at its own individual rate, a behavior known as its coefficient of thermal expansion (CTE).


When structures made from different materials -- such as a wide-bandgap semiconductor and a thermal shim -- are joined, it is vital that their thermal-expansion coefficients be identical. Bonded materials that expand at different rates separate readily.


Diamond has a very low coefficient of thermal expansion of about two parts per million/Kelvin (ppm/K). But the materials used to make wide-bandgap semiconductors -- such as silicon carbide or gallium nitride – have higher CTEs, generally in the range of three to five ppm/K.


By adding in just the right percentage of silver, which has a CTE of about 20 ppm/K, the GTRI team can tailor the silver-diamond composite to expand at the same rate as the semiconductor material. By matching thermal-expansion rates during heating and cooling, the researchers have enabled the two materials to maintain a strong bond.


Unlike metals, which conduct heat by moving electrons, diamond conducts heat by means of phonons, which are vibrational wave packets that travel through crystalline and other materials. Introducing silver between the diamond-particle interfaces helps phonons move from particle to particle and supports thermal efficiency.


"It's a challenge to use diamond particles to fill space in a plane with high efficiency and stability," Nadler said. "In recent years we've built image-analysis and other tools that let us perform structural morphological analyses on the material we've created. That data helps us understand what's actually happening within the composite -- including how the diamond-particle sizes are distributed and how the actually surrounds the ."


A remaining hurdle involves the need to move beyond performance testing to an in-depth analysis of the silver-diamond material's functionality. Nadler's aim is to explain the thermal conductivity of the composite from a fundamental materials standpoint, rather than relying solely on performance results.


The extremely small size of the thermal shims makes such in-depth testing difficult, because existing testing methods require larger amounts of material. However, Nadler and his team are evaluating several testbed technologies that hold promise for detailed thermal-conductivity analysis.