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University of Utah scientists want to turn wasted heat into useful energy

SALT LAKE CITY — New research from the University of Utah could blaze a path to help wasted energy become a source of added electrical power.

Scientists from the U.'s Department of Mechanical Engineering believe they have found a method that will turn excess heat into a useful energy source. The findings were published in the paper titled "A Near-Field Radiative Heat Transfer Device," in the journal Nature Nanotechnology.

Up to 2/3 of the energy consumed in the U.S. each year is wasted as heat, researchers said. Vehicle engines, laptops, mobile devices and refrigerators are examples of things that heat up with overuse, explained Mathieu Francoeur, University of Utah mechanical engineering associate professor.

University of Utah mechanical engineering associate professor Mathieu Francoeur holds a near-field radiative heat transfer device on his fingertip in the Radiative Energy Transfer Lab at the U. in Salt Lake City on Thursday, July 11, 2019. The device conv
University of Utah mechanical engineering associate professor Mathieu Francoeur holds a near-field radiative heat transfer device on his fingertip in the Radiative Energy Transfer Lab at the U. in Salt Lake City on Thursday, July 11, 2019. The device converts heat into energy.
Kristin Murphy, Deseret News

Capturing the excess heat to generate energy could be a significant improvement for consumers and industry, he said.

Francoeur, along with former U. mechanical engineering doctoral student John DeSutter and former U. mechanical engineering master’s student Lei Tang, co-authored the article detailing their discovery of a way to produce more electricity from heat by creating a silicon chip — known as a “device” — that converts more thermal radiation, or heat, into electricity.

"We can extract that heat from the processor using a device, and once we extract that heat, we convert it into radiation and then convert that into electricity that we can (put) back into the battery and increase the battery life," he said. In time, he wants to see the technology employed to develop applications for everyday use, which could happen in the next five years or so.

Researchers determined a theoretical “blackbody limit” to how much energy can be produced from thermal radiation. Francoeur and his colleagues have been able to demonstrate they can go far beyond the typical blackbody limit to generate more power by using a device with two silicon surfaces very close together, a news release stated

The team produced a 5--by-5-millimeter chip, about the size of a pencil eraser, using two silicon wafers separated by a nanoscopic gap that was approximately 100 nanometers in thickness — or one-thousandth the diameter of a human hair. The chip was placed in a vacuum, then heated on one side with another side cooled creating a heat flux that was able to produce electricity, the release stated.

University of Utah mechanical engineering associate professor Mathieu Francoeur holds a near-field radiative heat transfer device on his fingertip at the University of Utah in Salt Lake City on Thursday, July 11, 2019. The device converts heat into energy
University of Utah mechanical engineering associate professor Mathieu Francoeur holds a near-field radiative heat transfer device on his fingertip at the University of Utah in Salt Lake City on Thursday, July 11, 2019. The device converts heat into energy.
Kristin Murphy, Deseret News

While creating energy in this way is not unique, Francoeur and his team discovered a way to place the two silicon surfaces uniformly close together at a microscopic level without having them touch each other. The closer in proximity, the more energy that can be generated, he said.

“Nobody can emit more radiation than the blackbody limit,” he said. “But when we go to the nanoscale, you can.”

Francoeur said he one day envisions using such technology to not only cool portable devices like laptops or smartphones, but also to channel that heat into increased battery life.

"You can basically increase the lifetime of your battery by 50%," he said. "Heat is detrimental to the performance of your phone, so if you extract that heat you put that electrical power back in your battery."

He also said the chips could be used to improve the efficiency of solar panels by increasing the amount of electricity generated from the sun’s heat or in automobiles by extracting the heat from the vehicle's engine to help power its electrical systems. In the future, the chips could also be designed for use in implantable medical devices like a pacemaker, which would eliminate the need for replacing batteries, the release stated.

An added advantage with the technology would be improving the life of computer processors by keeping them cool — reducing overall wear and tear, he said. It would save energy that would otherwise power fans to cool the processors and the technology could also be environmentally beneficial, he noted.

“You put the heat back into the system as electricity,” Francoeur said. “Right now, we’re just dumping it into the atmosphere. It’s heating up your room, for example, and then you use your (air conditioner) to cool your room, which wastes more energy.”

"Our work is just one potential solution. It will not solve all the world's problems," he said. "We'll need different solutions and different types of technologies."