MIT: Better way to harness waste heat

CAMBRIDGE, Mass. – New MIT research points the way to a technology that might make it possible to harvest much of the wasted heat produced by everything from computer processor chips to car engines to electric powerplants, and turn it into usable electricity.

More than half of the energy consumed worldwide is wasted, most of it in the form of excess heat. This new technology would allow conversion of waste heat into electricity with an efficiency several times greater than existing devices. That kind of waste-energy harvesting might, for example, lead to cellphones with double the talk time, laptop computers that can operate twice as long before needing to be plugged in, or power plants that put out more electricity for a given amount of fuel.

Theory says that conversion of heat into electricity can never exceed a specific value called the Carnot Limit, based on a 19th-century formula for determining the maximum efficiency that any device can achieve in converting heat into work. But current commercial thermoelectric devices only achieve about one-tenth of that limit, says Peter Hagelstein, associate professor of electrical engineering. In experiments involving a different new technology, thermal diodes, Hagelstein worked with Yan Kucherov, a consultant for the Naval Research Laboratory, and coworkers to demonstrate efficiency as high as 40 percent of the Carnot Limit. The calculations show that this new kind of system could ultimately reach as much as 90 percent of that ceiling.

EurekAlert