Spectral selectivity or nonimaging optics: Which to use for radiative cooling?

2018 ◽  
Author(s):  
Harry N. Apostoleris ◽  
Matteo Chiesa
Keyword(s):  
Radiative Cooling ◽  
Spectral Selectivity ◽  
Nonimaging Optics

scholarly journals Theoretical and Experimental Study of Spectral Selectivity Surface for Both Solar Heating and Radiative Cooling

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Mingke Hu ◽  
Gang Pei ◽  
Lei Li ◽  
Renchun Zheng ◽  
Junfei Li ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Heating Surface ◽  
Solar Heating ◽  
Cooling Power ◽  
Radiative Cooling ◽  
Relative Temperature ◽  
Composite Surface ◽  
Spectral Selectivity ◽  
Atmospheric Window ◽  
Inclination Angles

A spectral selectivity surface for both solar heating and radiative cooling was proposed. It has a high spectral absorptivity (emissivity) in the solar radiation band and atmospheric window band (i.e., 0.2~3 μm and 8~13 μm), as well as a low absorptivity (emissivity) in other bands aside from the solar radiation and atmospheric window wavelengths (i.e., 3~8 μm or above 13 μm). A type of composite surface sample was trial-manufactured combining titanium-based solar selective absorbing coating with polyethylene terephthalate (TPET). Sample tests showed that the TPET composite surface has clear spectral selectivity in the spectra of solar heating and radiation cooling wavelengths. The equilibrium temperatures of the TPET surface under different sky conditions or different inclination angles of surface were tested at both day and night. Numerical analysis and comparisons among the TPET composite surface and three other typical surfaces were also performed. These comparisons indicated that the TPET composite surface had a relative heat efficiency of 76.8% of that of the conventional solar heating surface and a relative temperature difference of 75.0% of that of the conventional radiative cooling surface, with little difference in cooling power.

scholarly journals Simple PDMS/AIN emitter as a passive daytime radiative cooling design

2021 ◽  
Author(s):  
Mabchour ◽  
benlattar mourad
Keyword(s):  
Outer Space ◽  
Solar Spectrum ◽  
Ambient Air ◽  
Heat Radiation ◽  
Cooling Power ◽  
Radiative Cooling ◽  
Spectral Selectivity ◽  
Solar Energy Harvesting ◽  
Atmospheric Window ◽  
Cooling Design

Abstract Radiative cooling is a passive cooling purpose where a surface naturally cools by radiating the mid-infrared heat radiation to the cold outer space through the atmospheric window . Daytime passive radiative cooling technologies can be simply provided by using a multi-layer design that emits strongly in the transparency atmospheric window, while presents high reflectance in the solar spectrum . In this study, we propose a polydimethylsiloxane foil ) coated aluminum nitride (AIN) deposed onto silver (Ag) coated glass as a radiative cooler for enhancing both daytime and nighttime radiative cooling performances. The spectral selectivity of the proposed device was obtained using matrix method. Numerical results show that our proposed design can reflect more than 96 % in the solar spectrum, while its average emissivity in the atmospheric window can reach more than 90 %.In the absence of wind speed, the proposed device can achieve a net cooling power of under direct sunlight, cooling to a below the ambient air temperature. At nighttime, the proposed device temperature can drop by below the ambient, leading to a net cooling power of . Therefore, the proposed radiative design can fundamentally enable new methods for exploiting solar energy harvesting and energy conservation.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

Cellulose-Based Hybrid Structural Material for Radiative Cooling

Nano Letters ◽  
2020 ◽  
Author(s):  
Yipeng Chen ◽  
Baokang Dang ◽  
Jinzhou Fu ◽  
Chao Wang ◽  
Caicai Li ◽  
...  
Keyword(s):  
Structural Material ◽  
Radiative Cooling

scholarly journals Wearable Optoelectronics: Outdoor‐Useable, Wireless/Battery‐Free Patch‐Type Tissue Oximeter with Radiative Cooling (Adv. Sci. 10/2021)

2021 ◽  
Vol 8 (10) ◽  
pp. 2170057
Author(s):  
Min Hyung Kang ◽  
Gil Ju Lee ◽  
Joong Hoon Lee ◽  
Min Seok Kim ◽  
Zheng Yan ◽  
...  
Keyword(s):  
Radiative Cooling ◽  
Patch Type

scholarly journals Adaptive covers for combined radiative cooling and solar heating. A review of existing technology and materials

2021 ◽  
Vol 230 ◽  
pp. 111275
Author(s):  
Roger Vilà ◽  
Ingrid Martorell ◽  
Marc Medrano ◽  
Albert Castell
Keyword(s):  
Solar Heating ◽  
Radiative Cooling
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