A spectrally selective surface structure for combined photothermic conversion and radiative sky cooling
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RESEARCH ARTICLE
Bin ZHAO, Xianze AO, Nuo CHEN, Qingdong XUAN, Mingke HU, Gang PEI
A spectrally selective surface structure for combined photothermic conversion and radiative sky cooling
© Higher Education Press 2020
Abstract The sun and outer space are the ultimate heat and cold sources for the earth, respectively. They have significant potential for renewable energy harvesting. In this paper, a spectrally selective surface structure that has a planar polydimethylsiloxane layer covering a solar absorber is conceptually proposed and optically designed for the combination of photothermic conversion (PT) and nighttime radiative sky cooling (RC). An optical simulation is conducted whose result shows that the designed surface structure (i.e., PT-RC surface structure) has a strong solar absorption coefficient of 0.92 and simultaneously emits as a mid-infrared spectral-selective emitter with an average emissivity of 0.84 within the atmospheric window. A thermal analysis prediction reveals that the designed PTRC surface structure can be heated to 79.1°C higher than the ambient temperature in the daytime and passively cooled below the ambient temperature of approximately 10°C in the nighttime, indicating that the designed PT-RC surface structure has the potential for integrated PT conversion and nighttime RC utilization. Keywords solar energy, photothermic conversion, radiative sky cooling, spectral selectivity, multilayer film
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Introduction
The practice of harvesting heat and coolness for buildings Received Feb. 15, 2020; accepted May 15, 2020; online Sept. 15, 2020
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Bin ZHAO, Xianze AO, Nuo CHEN, Qingdong XUAN, Gang PEI ( ) Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei 230027, China E-mail: [email protected]
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Mingke HU ( ) Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei 230027, China; Institute of Sustainable Energy Technology, University of Nottingham, University Park, Nottingham NG7 2RD, UK E-mail: [email protected]
from renewable energy sources has recently been a hot topic in energy fields. Photothermic conversion (PT) is one such method to provide heat for buildings and there are already numerous kinds of commercial PT products for energy saving of buildings, such as the flat-plate solar collector [1], the evacuated tube collector [2], and the trombe wall [3]. Recently, radiative sky cooling (RC) has been widely investigated as an alternative cooling method to provide cooling and/or dissipate heat passively, and, it has successfully applied in many potential applications such as building-scale cooling supply [4], radiative cooling of solar cells [5,6], personal thermal management [7], and power generation [8]. The principle of RC is that heat is radiated from the surface to the cold outer space in the form of electromagnetic waves, relying on the transparent “atmospheric window” to allow thermal emission within the wavelength range of 8 to 13 mm to effectively escape to the uni
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