A scalable manufactured metamaterial — an engineered material with extraordinary properties not found in nature — to act as a kind of air conditioning system for structures and even under direct sunlight has the ability to cool objects with zero energy and water consumption — has been developed by a team of University engineers of Colorado Boulde.
The metamaterial film when applied to surface cools the object underneath by efficiently reflecting incoming solar energy back into space while simultaneously allowing the surface to shed its own heat in the form of infrared thermal radiation.
As described, in the journal Science, the new material can provide supplementary cooling for thermoelectric power plants which could be eco-friendly, to maintain the operating temperatures of their machinery the thermoelectric power plants currently require large amounts of water and electricity.
The researchers’ glass-polymer hybrid material is a potentially viable large-scale technology for both residential and commercial applications as it measures just 50 micrometers thick — slightly thicker than the aluminium foil found in a kitchen — and can be manufactured economically on rolls.
Xiaobo Yin, co-director of the research and an assistant professor holds dual appointments in CU Boulder’s Department of Mechanical Engineering and the Materials Science and Engineering Program. Yin had received DARPA’s Young Faculty Award in 2015.
“We feel that this low-cost manufacturing process will be transformative for real-world applications of this radiative cooling technology,” said Xiaobo Yin.
The material takes advantage of passive radiative cooling, the process by which objects naturally shed heat in the form of infrared radiation, without consuming energy. Some natural night-time cooling is provided by Thermal radiation and it can also be used in some areas for residential cooling, but cooling during the daytime has historically been more of a challenge. Even a small amount of directly-absorbed solar energy is enough to negate passive radiation for a structure exposed to sunlight.
The CU Boulder researchers challenge was to create a material that could provide a one-two punch: reflect any incoming solar rays back into the atmosphere while still providing infrared radiation with a means of escape. In order to solve this, visibly-scattering but infrared-radiant glass microspheres were embedded by the researchers into a polymer film. So, maximum spectral reflectance can be achieved after a thin silver coating was added by them underneath.
Ronggui Yang, also a professor of mechanical engineering and a Fellow of the American Society of Mechanical Engineers said, “Both the glass-polymer metamaterial formation and the silver coating are manufactured at scale on roll-to-roll processes.”
In Boulder, Colorado and Cave Creek, Arizona, the metamaterial during field tests successfully demonstrated its average radiative cooling power larger than 110W/m2 for continuous 72 hours and larger than 90W/m2 in direct, noon-time sunlight. Roughly that cooling power is equivalent to the electricity generated using solar cells for similar area, but both day and night the radiative cooling has the advantage of continuous running.
Gang Tan, an associate professor in the University of Wyoming’s Department of Civil and Architectural Engineering and a co-author of the paper said,” Just 10 to 20 square meters of this material on the rooftop could nicely cool down a single-family house in summer.”
The material could also help improve the efficiency and lifetime of solar panels, in addition to being useful for cooling of buildings and power plants. Panels can overheat to temperatures that hamper their ability to convert solar rays into electricity in direct sunlight.
“Just by applying this material to the surface of a solar panel, we can cool the panel and recover an additional one to two percent of solar efficiency,” said Yin. “That makes a big difference at scale.”
A patent has been applied by the engineers for the technology and they are working with CU Boulder’s Technology Transfer Office to explore potential commercial applications. They plan on creating a 200-square-meter “cooling farm” prototype in Boulder in 2017.
A $3 million grant was awarded in 2015 to Yang, Yin and Tang by the Energy Department’s Advanced Research Projects Agency-Energy (ARPA-E) and the invention is the result of this.
“The key advantage of this technology is that it works 24/7 with no electricity or water usage,” said Yang “We’re excited about the opportunity to explore potential uses in the power industry, aerospace, agriculture and more.”
News Source: sciencedaily.com
Picture source: google.co.in