Device could convert waste heat into electricity

Source :MIT News

An MIT scientist and a colleague have invented a semiconductor technology that could allow efficient, affordable production of electricity from a variety of energy sources–including waste heat–without a turbine or similar generator. The researchers presented the work at a Nov. 27 poster session during the Materials Research Society’s fall meeting in Boston.

Many researchers have worked to convert heat to electricity directly without using the moving parts of a generator. Among other advantages, such a device would be virtually silent, vibration-free and low in maintenance costs. Until now, however, the efficiency of such devices has been a problem. The amount of electricity they produce from a given amount of energy has been low.

The new device is twice as efficient as its closest commercial competitor. “That such good results were obtained in the first generation of the new device technology … indicates that the general approach has great promise for improved performance in more mature implementations,” wrote Associate Professor Peter L. Hagelstein of electrical engineering and computer science and Dr. Yan Kucherov of ENECO, Inc., in the paper accompanying their poster.

The new technology could have major implications for the recovery of waste heat from power plants and automobiles. For example, the heat lost through engine exhausts might be captured by the technology and converted into electricity to augment or replace a vehicle’s electrical and air conditioning systems. It could also be important in the primary generation of electrical power.

The technology is based on thermionics, which originated nearly a century ago with the basic vacuum tube, which consisted of two parallel conductive plates (cathode and anode) separated by a vacuum gap. In this high-temperature tube, electrons boiled off the cathode, traversed the gap and then were absorbed into the colder anode. The conversion of heat to electricity “occurs as the electrons transport ‘uphill’ against an electric field in the gap region,” said Hagelstein, who is also affiliated with Research Laboratory of Electronics.

These early “vacuum gap” designs had prohibitive manufacturing costs and high operating temperatures–above 1,000 degrees C (about 2,000 degrees F)–which have limited the technology to nuclear-powered converters in space probes, satellites and special military systems.

The new technology essentially replaces the traditional vacuum gap with a multilayer semiconductor structure. Hagelstein credits Professor Gerald D. Mahan of the University of Tennessee with first suggesting such a solid-state implementation of vacuum thermionics. Hagelstein and Kucherov demonstrated two basic enabling physical mechanisms that allow this technology to be implemented practically.

Louis D. Smullin, professor emeritus of electrical engineering, said of the new work: “Thermocouples and thermopiles have been with us for over a century. I believe that these new devices represent the first big step in performance of these devices. In the 50s there was much hope that direct conversion of heat to electricity would open up a new era, but it was not to be. With these new devices, maybe these dreams will come true.”

By careful selection of materials, ENECO scientists are creating highly efficient, solid-state conversion devices, called “thermal diodes,” that will operate from 200 to 450 degrees C–typical temperatures for waste heat and for concentrated solar radiation.

An added plus: the technology is environmentally friendly. “Solid-state thermal-to-electric energy conversion converts energy due to how electrons transport in the conductor, a process that generates no pollution,” Hagelstein said. He noted, however, that some of the materials used in the present generation of devices are toxic, which will affect the eventual disposal of the devices.

The work has been sponsored by ENECO with additional support from the Defense Advanced Research Projects Agency. Technical development is now focused on optimizing the types of materials used in buliding the thermal diodes.

Hagelstein is a technical consultant for ENECO, which is developing the technology and has applied for patents in the United States and Europe. At least one patent has been issued.

A version of this article appeared in MIT Tech Talk on December 5, 2001.

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Why we should have a climate change agreement

Today, the Kyoto Protocol regulates the greenhouse gas emissions up to 2012.

If the world’s nations are to decide upon a new agreement to enter into force before the first commitment period of the Kyoto Protocol expires, 2009 is the final opportunity to do so.

A global climate change agreement is necessary so that we can limit the negative man-made effects on the climate system for future generations.

Global climate changes have always taken place. There have been ice ages and warm periods. Ice core drilling has shown how temperatures and emissions of greenhouse gases have fluctuated over the last 650,000 years. Greenhouse gases in the atmosphere have not been the decisive factor for the temperature swings, but they have contributed to intensifying them.

Climate changes in themselves are nothing new. What is new is that man-made emissions have led to the volume of greenhouse gases in the atmosphere being increased massively, and for that reason global warming is happening significantly faster than previously.

Source :#
# Ministry of Foreign Affairs of Denmark

UN climate chief Yvo de Boer :A day before “The Copenhagen” start

A day before two weeks of climate talks in the Danish capital formally begin, the UN climate chief on Sunday said time was up to agree on the framework of a tougher climate deal after troubled negotiations have deepened a rift between rich and poor nations.

“I believe that negotiators now have the clearest signal ever from world leaders to draft a solid set of proposals to implement rapid action,” Yvo de Boer told reporters, according to Reuters.

“Never in the 17 years of climate change negotiations have so many different nations made so many firm pledges together. Almost every day countries announce new targets or plans of action to cut emissions,” he said.

In recent weeks, China, India, Indonesia and other countries have announced commitments to reduce emissions, raising hopes of success in Copenhagen.

South Africa on Sunday became the latest country to announce an emissions target. It said over the next 10 years it would reduce emissions by 34 percent from “business as usual,” the level they would reach under ordinary circumstances, AP reports. By 2025 that figure would peak at 42 percent, effectively leveling off and thereafter begin to decline.

Japan said on Sunday it would stick with its target to cut emissions by 25 percent from 1990 levels by 2020, although the pledge depends on all major emitters, including China and the United States, being ambitious.

The closing stages of the UN conference will be attended by 105 world leaders who will try to seal a deal after years of bitter debates over how to divide up the burden of emissions curbs and who should pay.

Source : The Copenhagen

The Copenhagen Starting from today

Good Morning People ,
United Nations 15th Climate Change conference “The Copenhagen” is starting from today in Denmark.We all are hoping for some good , collaborative descions out of this conference .

See u ahead …

What is the greenhouse effect and global warming?

The greenhouse effect is a natural mechanism that retains the heat emitted from the earth’s surface. The earth’s average temperature is at the moment around 14 degrees celsius (57 degrees fahrenheit). If the natural greenhouse effect did not exist, the average temperature would be around minus 19 degrees celsius (minus 2 degrees fahrenheit).

The greenhouse effect is caused by a range of different gases in the earth’s atmosphere. Water vapour makes the most significant contribution to the greenhouse effect, followed by CO2. The atmospheric content of greenhouse gases – in particular CO2 – and the consequences for the climate are being discussed because the content of these gases in the atmosphere has risen precipitously in a period covering approximately the latest 250 years, and especially the last 50.

At present the concentration of CO2 in the atmosphere is about 385 ppm (parts per million). Before industrialization it was about 280 ppm. Analyses of air contained in ice from the Antarctic ice cap show that there is far more CO2 in the air today than at any time in the last 650,000 years.

The consequence is that the greenhouse effect is becoming stronger, and therefore the earth is becoming warmer. How much warmer has, however, been a matter of dispute. The most recent assessment report from the IPCC is from 2007. It concludes that the earth’s average temperature has risen by 0.74 degrees in the period from 1906 to 2005. The warming is stronger over land areas than over the sea, and accordingly it is strongest in the northern hemisphere. At the same time occurrences of heat waves and violent downpours have also increased, the oceans have risen, and the ice at the world’s poles and on its mountains has begun to melt. All of these effects are predictable in the event of global warming.

The IPCC’s most recent assessment report concludes that the average temperature will continue to rise, but that the extent and the duration of this rise, and the severity of its consequences, depend on how quickly and how effectively emissions of greenhouse gases can be restricted and, over time, reduced. (Photo: Scanpix/Reuters)

Reference :-http://en.cop15.dk/climate+facts/background+articles/what+isthe+greenhouse+effect

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