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HOUSTON, June 23, 2015 - Researchers from the University of Houston have devised a new formula for calculating the maximum efficiency of thermoelectric materials, the first new formula in more than a half-century, designed to speed up the development of new materials suitable for practical use.
By using the new formula for calculation, which relies upon newly developed measurements for the figure of merit and power factor of a material - called the engineering figure of merit, or (ZT)eng, and engineering power factor, or (PF)eng - scientists will be able to determine whether devices based on a material would generate energy efficiently enough to be worth pursuing, said Zhifeng Ren, principal investigator at the Texas Center for Superconductivity at UH (TcSUH).
"This is a form for the quick screening of materials," said Ren, who is also M.D. Anderson Chair professor of physics at UH. "If the engineering ZT is not high enough, don't waste your time trying to build a device.
"The new formula for calculation is explained in a paper published in the Proceedings of the National Academy of Sciences. Ren was lead author, working with Gang Chen, an engineer at the Massachusetts Institute of Technology; Paul Ching-Wu Chu, T.L.L. Temple Chair of Science and founding director of TcSUH; and Hee Seok Kim and Weishu Liu, both physicists and researchers at TcSUH.
Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area, and the formula still widely used in the field dates to the 1950s, created by Russian physicist Abram F. Ioffe.
In thermoelectric materials, efficiency is calculated as the measure of how well it converts heat - often waste heat generated by power plants or other industrial processes - into power. For example, a material that takes in 100 watts of heat and produces 10 watts of electricity has an efficiency rate of 10 percent. Top efficiency for current thermoelectric materials is about 12 percent, Ren said.
Ioffe's formula assumes the thermoelectric properties remain constant despite the variation in temperature along the length of the material, Ren said. That isn't the case for many materials, and the Ioffe formula is accurate only for thermoelectric materials that operate within a small range of temperatures or those in which the relationship between the dimensionless figure of merit ZT and temperature progresses in a linear fashion.
But that relationship often isn't linear, making the efficiency value produced by the Ioffe formula inaccurate, Ren said. That means new materials with high peak ZT, determined to be highly efficient according to the Ioffe formula, may not work as well in practice if the (ZT)eng is not also high, he said.
"The conventional efficiency formula often misleads and gives rise to an impractically high efficiency prediction," the researchers wrote. "For this reason, it is desirable to establish a new model to predict the energy conversion efficiency based on the temperature-dependent individual TE (thermoelectric) properties for devices operating under a large temperature difference."
The researchers actually report two new formulas, one of which also takes into account the Thomson effect, the heat produced by Seebeck when it is temperature dependent along its length. That formula can be used to determine maximum efficiency for any thermoelectric material, Ren said; the other formula developed by the researchers can be used when Thomson heat is ignored.
For more information, read the original news release.
Three scientists have been named as recipients of the 2015 Bernd T. Matthias Prize for Superconducting Materials, an international prize awarded for innovative contributions to the field. The winners are Xianhui Chen of the University of Science and Technology of China, Zachary Fisk of the University of California-Irvine and Zhongxian Zhao of the Institute of Physics, Chinese Academy of Science in Beijing.
The prize was created in 1989 by friends and colleagues of Bernd T. Matthias, a German-born physicist who immigrated to the United States in 1947 and is noted for his discovery of nearly 1,000 superconducting materials. The Texas Center for Superconductivity at the University of Houston (TcSUH) has sponsored the prize since 2000.
In addition to sharing the $6,000 prize, each winner will receive a framed certificate designed by Elsevier Publishers. The prize will be formally presented during the 2015 M2S-HTSC international conference in Geneva, Switzerland, in August.
For more information, read the original news release.
Three UK companies have been revealed as the finalists for this year’s Royal Academy of Engineering MacRobert Award.
Artemis Intelligent Power has been selected for its technology to unlock the power potential of wind turbines; Endomag has been chosen for its system that is improving the diagnosis of cancer spread in breast cancer patients; and Victrex for its creation of new materials to bring modern technology advances to life.
Synonymous with spotting the ‘next big thing’ in the technology sector, the MacRobert Award is the UK’s longest running national prize for engineering innovation. Since 1969, the Award has identified world-changing innovations with tangible societal benefit and proven commercial success.
Many previous winning technologies are now ubiquitous in modern medicine, transport and technology. The very first award in 1969 went to the Rolls-Royce Pegasus engine, used in the iconic Harrier jets, and in 1972 the judges recognised the extraordinary potential of the first CT scanner – seven years before its inventor Sir Godfrey Hounsfield received the Nobel Prize.
Last year’s winner, SME Cobalt Light Systems, won for the innovation behind an airport security liquid scanner that can now be found in over 65 airports throughout Europe. The same technology is also being used to detect counterfeit goods and analyse food.
This year’s three MacRobert Award finalists, who have each shown remarkable promise in their respective domains, are all competing for a gold medal and a £50,000 cash prize. The winner will be announced on 16 July 2015 at the Academy's annual awards dinner in London.
Edinburgh-based Artemis Intelligent Power has developed a digital hydraulic power system that unlocks the ability to generate much greater levels of power from offshore wind turbines. As well as dramatically improving power capacity, the smart, modular system has been designed to overcome the significant reliability issues associated with existing turbines. Artemis is already developing world-leading systems, dramatically improving turbine efficiency and with it the prospects for future exploitation of wind power.
Niall Caldwell, Artemis’s managing director, said: “By combining the intelligence of digital control with the robustness and low cost of hydraulic machines, the Artemis team of engineers has made a fundamental advance in the scale and efficiency of mechanical power transmission. Digital Displacement® technology will bring down the costs of generating renewable energy and reduce fuel use in transport and industry. Our business shares the mission of our parent company to be a manufacturer for the sustainability of the earth and humankind.”
Team members: Dr Niall Caldwell, Managing Director; Pierre Joly, Operations Director; Dr Win Rampen FREng, Chairman; Professor Stephen Salter FRSE, Non-Executive Director; Dr Uwe Stein, Chief Engineer.
Endomag is based in Cambridge and has pioneered a new breast cancer diagnostic tool that avoids the use of radioactive tracers in determining the spread of cancer through the lymphatic system. The cost and logistical challenges of relying on radioactive material have meant that sentinel lymph node biopsy – currently the best method of breast cancer staging – is only available to one in six patients globally, creating a ‘postcode lottery’ for effective diagnosis. The SentiMag probe developed by Endomag identifies sentinel lymph nodes for removal by detecting a magnetic, rather than radioactive, tracer signal.
Dr Eric Mayes, Chief Executive Officer of Endomag, said: “Endomag is extremely honoured by this recognition, both for the hard work of our founding team and how we have since translated this engineering innovation to meet the needs of so many patients.”
Team members: Professor Quentin Pankhurst, Founder; Simon Hattersley, Founder; Dr Audrius Brazdeikis, Founder; Dr Eric Mayes, Chief Executive Officer.
Blackpool-based Victrex has created the highest performing ultra-thin polymers (plastics) in the world. Initially enabling smartphone speakers and earbuds to produce high-quality sound without risk of failure, they could now be a key material for enabling the flexible electronics revolution. In forms up to 20 times thinner than a human hair, the PEEK polymer is already found in over a billion consumer electronic devices and is also used as a lightweight replacement for metal in aircraft, cars and medical implants.
John Grasmeder, Technical Director for Victrex plc, said: “Victrex is a world leader in high performance polymers and to be in the running for the MacRobert award is a real testament to the capability, innovation focus and performance of our people.
“Technical and manufacturing excellence are key pillars of our strategy. Being able to understand market needs and work closely with our customers in developing solutions to their challenges requires real technical and manufacturing know-how. APTIV film has been a success story for Victrex in recent years and we continue to explore opportunities in Electronics and across our other markets.”
Team members: Mike Percy, Global Technical Manager, APTIV; Kyri Christodoulou, Films Quality Improvement Manager; John Parkinson, Quality Support Engineer; Jason Li, Development Engineer.
The MacRobert Award is determined by a panel of 10 judges representing a broad spectrum of engineering expertise and each a leader in their field.
Dame Sue Ion DBE FREng, Chair of the MacRobert Award judging panel, said, “Each of this year’s finalists has demonstrated remarkable drive and determination to achieve technical advances that can make a considerable difference to many aspects of our lives. The variety and standard of engineering skills behind each innovation is testament to the UK’s strength in the sector.
“Innovative engineering is the key to our future growth in the UK and we will have to make increasing use of our knowledge and creative talent if we are to take advantage of this opportunity. These three companies are great examples of engineering for growth in action.”
- See more at: http://www.raeng.org.uk/news/news-releases/2015/may/three-engineering-pioneers-in-the-running-for-2015#sthash.hCgbwvFp.dpuf
For more information, read the original news release.
UH RESEARCHERS DISCOVER NEW MATERIAL TO PRODUCE CLEAN ENERGY
New Material Shows Value of High Power Factor, High-Output Power Materials
Houston, March 4, 2015 – Researchers at the University of Houston have created a new thermoelectric material, intended to generate electric power from waste heat – from a vehicle tailpipe, for example, or an industrial smokestack – with greater efficiency and higher output power than currently available materials.
The material, germanium-doped magnesium stannide, is described in the current issue of the Proceedings of the National Academy of Sciences. Zhifeng Ren, lead author of the article and M.D. Anderson Chair professor of physics at UH, said the new material has a peak power factor of 55, with a figure of merit – a key factor to determine efficiency – of 1.4.
The new material – the chemical compound is Mg2Sn0.75Ge0.25 – is important in its own right, Ren said, and he has formed a company, called APower, to commercialize the material, along with frequent collaborator Gang Chen of the Massachusetts Institute of Technology and two former students.
But he said another key point made in the paper is the importance of looking for materials with a high power factor, or output power density, in addition to the traditional focus on a high figure of merit, or efficiency, commonly referred to as ZT.
“Everyone pursued higher ZT,” he said. “That’s still true. But the way everybody pursued higher ZT is by reducing thermal conductivity. We were, too. But the reduction of thermal conductivity is limited. We need to increase the power factor. If thermal conductivity remains the same and you increase the power factor, you get higher ZT.”
Thermoelectric materials produce electricity by exploiting the flow of current from a warmer area to a cooler area. In the germanium-doped magnesium stannide, the current is carried by electrons.
“Pursuing high ZT has been the focus of the entire thermoelectric community …” the researchers wrote. “However, for practical applications, efficiency is not the only concern, and high output power density is as important as efficiency when the capacity of the heat source is huge (such as solar heat), or the cost of the heat source is not a big factor (such as waste heat from automobiles, steel industry, etc.)”
Germanium-doped magnesium stannide has a fairly standard figure of merit, at 1.4, but a high power factor, at 55, the researchers report. That, coupled with a raw material cost of about $190 per kilogram, according to the U.S. Geological Survey Data Series, makes it commercially viable, they said.
Ren, who also is a principal investigator at the Texas Center for Superconductivity at UH, said several competing materials have lower power factors and also more expensive raw materials.
The material was created through mechanical ball milling and direct current-induced hot pressing. It can be used with waste-heat applications and concentrated solar energy conversion at temperatures up to 300 degrees Centigrade, or about 572 degrees Fahrenheit, Ren said. He said typical applications would include use in a car exhaust system to convert heat into electricity to power the car’s electric system, boosting mileage, or in a cement plant, capturing waste heat from a smokestack to power the plant’s systems.
In addition to Ren, researchers on the paper include Weishu Liu, Hee Seok Kim, Shuo Chen, Qing Jie, Bing Lv and Paul Ching-Wu Chu, all of the UH physics department and the Texas Center for Superconductivity; Mengliang Yao, Zhensong Ren and Cyril P. Opeil of Boston College, and Stephen Wilson of the University of California at Santa Barbara.
Shuo Chen, an assistant professor in the Department of Physics, has been awarded a Robert A. Welch Professorship in High Temperature Superconductivity and Materials Physics from the Texas Center for Superconductivity at the University of Houston (TcSUH). The Robert A. Welch Foundation created the two-year professorships to support outstanding faculty, research faculty and visiting scientists.
The appointment was effective Oct. 1.
“Understanding physical properties of materials are of great importance for their vast applications,” Chen said. “I am appreciative of the support from the Robert A. Welch Professorship to accelerate my work on exploring novel physics in materials for electronics, energy and superconductivity.”
Her research includes synthesis, in situ electron microscopy and device application of materials. She aims to discover new physics and materials in superconductivity, electrocatalysis for fuel and energy generation, thermoelectrics for heat-electricity conversion, batteries for energy storage and phase change materials for electronics.
She is particularly interested in interfacial mass and electrical and thermal transport properties in materials. Such transport phenomena can play dominant roles in materials, especially where there are a large amount of nanostructures.
With her expertise in materials synthesis and in situ electron microscopy, she intends to fabricate individual nanostructures and interfaces, then apply in situ atomic resolution electron microscopy for simultaneously acquiring structures and transport properties in nanoscale interfaces with controllable temperature, electrical and mechanical conditions. Ultimately, she plans to apply the fundamental understanding gained to design superior materials for applications.
Allan J. Jacobson, TcSUH director and the Robert A. Welch Chair of Science in the UH chemistry department, said he is pleased the Center for Superconductivity is expanding its energy materials program.
“We look forward to Chen’s exciting research,” he said.
For more information, read the original news release.
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