CORVALLIS, Ore. - Researchers at Oregon State University have demonstrated a highly efficient method to capture the low-to-medium grade waste heat produced by automobiles, diesel generators, or being wasted by factories and electrical utilities and use much of that heat either for cooling or the production of electricity. A prototype has been completed to show the effectiveness of this technology.

“This could become a very important new energy source and way to improve energy efficiency,” said Hailei Wang, a research associate in the School of Mechanical, Industrial and Manufacturing Engineering at Oregon State University. “The prototype shows that these systems work as well as we expected they would.”

More than half of the heat generated by industrial activities is now wasted, Wang said, and even very advanced electrical power plants only convert about 40 percent of the energy produced into electricity. The internal combustion engines of automobiles are even worse - they generally operate around 25-40 percent conversion efficiency. The very function of an automobile radiator is to dissipate wasted heat.

Various approaches have been attempted, and are sometimes used, to capture and use at least some of that waste heat to produce cooling. The new system being developed at Oregon State may do that as, or more, efficiently than past approaches, be more portable, and also have one major advantage - the ability to also produce electricity.

It’s called a “thermally activated cooling system” that gains much of its efficiency by using extraordinarily small microchannels which help to better meet the performance, size, and weight challenges. It effectively combines a vapor compression cycle with an “organic Rankine cycle,” an existing energy conversion technology.

The new prototype completed at Oregon State succeeded in turning 80 percent of every kilowatt of waste heat into a kilowatt of cooling capability. Researchers say the conversion efficiency wouldn’t be nearly as high if the goal is to produce electricity - about 15-20 percent - but it’s still much better than the current approach, which is to waste the energy potential of all of the heat.

“This technology would be especially useful if there’s a need to have cooling systems where heat is being wasted,” Wang said. “That’s one reason the research has been supported by the Department of Defense, because they see it being used to provide needed air conditioning for electronics and other purposes when they are using generators in the field.”

However, the Oregon State scientists said that may be just the beginning. Factories often produce enormous amounts of wasted heat in their operations. The systems could also be incorporated into alternative energy technologies such as solar or geothermal, the scientists said, in addition to fossil fuel use.

Conceptually, it should also be possible for such systems to be used in hybrid automotive technology, taking waste heat from the gasoline engine and using it not only for air conditioning but also to help recharge the battery that powers the vehicle, Wang said.

Continued research will be needed to perfect the technology and adapt it to different uses, the scientists said.

The work takes advantage of Oregon State’s advanced programs in microchannel technology, a key focus of the Microproducts Breakthrough Institute operated by Oregon State University and the Pacific Northwest National Laboratory. This study was co-authored by Rich Peterson, an Oregon State professor of mechanical engineering, expert in thermal sciences and energy systems, and associate director of the Microproducts Breakthrough Institute.

Publication date: 06/20/2011