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Title: Selective radiative cooling with MgO and/or LiF layers

Abstract

A selective radiation cooling material which is absorptive only in the 8 to 13 microns wavelength range is accomplished by placing ceramic magnesium oxide and/or polycrystalline lithium fluoride on an infrared-reflective substrate. The reflecting substrate may be a metallic coating, foil or sheet, such as aluminum, which reflects all atmospheric radiation from 0.3 to 8 microns, the magnesium oxide and lithium fluoride being nonabsorptive at those wavelengths. <10% of submicron voids in the material is permissible in which case the MgO and/or LiF layer is diffusely scattering, but still nonabsorbing, in the wavelength range of 0.3 to 8 microns. At wavelengths from 8 to 13 microns, the magnesium oxide and lithium fluoride radiate power through the ''window'' in the atmosphere, and thus remove heat from the reflecting sheet of material and the attached object to be cooled. At wavelengths longer than 13 microns, the magnesium oxide and lithium fluoride reflects the atmospheric radiation back into the atmosphere. This high reflectance is only obtained if the surface is sufficiently smooth: roughness on a scale of 1 micron is permissible but roughness on a scale of 10 microns is not. An infrared-transmitting cover or shield is mounted in spaced relationship to themore » material to reduce convective heat transfer. If this is utilized in direct sunlight, the infrared transmitting cover or shield should be opaque in the solar spectrum of 0.3 to 3 microns.« less

Inventors:
Issue Date:
OSTI Identifier:
5910375
Application Number:
ON: DE85011595
Assignee:
Dept. of Energy ERA-10-025944; EDB-85-079680
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Patent
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; RADIATIVE COOLING; INFRARED RADIATION; LAYERS; LITHIUM FLUORIDES; MAGNESIUM OXIDES; REFLECTION; ALKALI METAL COMPOUNDS; ALKALINE EARTH METAL COMPOUNDS; CHALCOGENIDES; COOLING; ELECTROMAGNETIC RADIATION; FLUORIDES; FLUORINE COMPOUNDS; HALIDES; HALOGEN COMPOUNDS; LITHIUM COMPOUNDS; LITHIUM HALIDES; MAGNESIUM COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; RADIATIONS; 420400* - Engineering- Heat Transfer & Fluid Flow

Citation Formats

Berdahl, P.H. Selective radiative cooling with MgO and/or LiF layers. United States: N. p., 1984. Web.
Berdahl, P.H. Selective radiative cooling with MgO and/or LiF layers. United States.
Berdahl, P.H. Fri . "Selective radiative cooling with MgO and/or LiF layers". United States.
@article{osti_5910375,
title = {Selective radiative cooling with MgO and/or LiF layers},
author = {Berdahl, P.H.},
abstractNote = {A selective radiation cooling material which is absorptive only in the 8 to 13 microns wavelength range is accomplished by placing ceramic magnesium oxide and/or polycrystalline lithium fluoride on an infrared-reflective substrate. The reflecting substrate may be a metallic coating, foil or sheet, such as aluminum, which reflects all atmospheric radiation from 0.3 to 8 microns, the magnesium oxide and lithium fluoride being nonabsorptive at those wavelengths. <10% of submicron voids in the material is permissible in which case the MgO and/or LiF layer is diffusely scattering, but still nonabsorbing, in the wavelength range of 0.3 to 8 microns. At wavelengths from 8 to 13 microns, the magnesium oxide and lithium fluoride radiate power through the ''window'' in the atmosphere, and thus remove heat from the reflecting sheet of material and the attached object to be cooled. At wavelengths longer than 13 microns, the magnesium oxide and lithium fluoride reflects the atmospheric radiation back into the atmosphere. This high reflectance is only obtained if the surface is sufficiently smooth: roughness on a scale of 1 micron is permissible but roughness on a scale of 10 microns is not. An infrared-transmitting cover or shield is mounted in spaced relationship to the material to reduce convective heat transfer. If this is utilized in direct sunlight, the infrared transmitting cover or shield should be opaque in the solar spectrum of 0.3 to 3 microns.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1984},
month = {9}
}