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Ronggui Yang1 Xiaobo Yin1 Dongliang Zhao1 Yao Zhai1

1, University of Colorado Boulder, Boulder, Colorado, United States

Fresh water withdrawal for thermoelectric power generation accounts for approximately 41% of all fresh water withdrawal in the US while 3% of cooling tower water load is evaporated and dissipated. Dry-cooling systems suffer from two major drawbacks: 1) the low air-side heat transfer coefficient, and 2) the performance penalty when ambient temperature is high. Radiative cooling has been proposed as supplemental cooling, which has no water dissipation to the atmosphere and no loss of power plant efficiency. We have developed a scalable manufactured metamaterial—an engineered material with extraordinary properties not found in nature -- a 50-micron thick polymer film randomly filled with glass microspheres of 8-micron diameter, and backed with a 100nm silver coating. While the film reflects almost all sunlight, the microspheres interact strongly with infrared radiation to emit heat at high enough rates to achieve a net cooling effect. We have demonstrated an average radiative cooling flux greater than 110 W/m2 in a continuous three-day field test and more than 90 W/m2 cooling power was observed under direct sunshine. However, due to the intrinsic low density of radiative cooling flux, cold collection becomes crucial for many engineering applications. With the ability demonstrated for radiative cooling to cool down water 10°C below ambient temperature at noon time under the sun. We propose a radiative cooled-cold collection and storage (RadiCold) system with operation scheduling to produce cold water at a constant sub-ambient temperature with reduced operational cost. The RadiCold system can be either used directly for air conditioning in buildings, or coupled to other energy systems for energy saving. The integration of the RadiCold system with a dry-cooling power plant can significantly increase the thermoelectric power conversion efficiency while reducing water consumption.

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