Radiative cooling structures and systems

Abstract

Polymer-based selective radiative cooling structures are provided which include a selectively emissive layer of a polymer or a polymer matrix composite material. Exemplary selective radiative cooling structures are in the form of a sheet, film or coating. Also provided are methods for removing heat from a body by selective thermal radiation using polymer-based selective radiative cooling structures.

We claim: 
     
         1 . A selective radiative cooling structure, the structure comprising
 a selectively emissive layer comprising a polymer and a plurality of dielectric particles dispersed in the polymer, where the dielectric particles have an average size ranging from 3 μm to 30 μm;   wherein the selective radiative cooling structure has an average emissivity ranging from 0.6 to 1.0 over the wavelength range 7 μm to 13 μm; the volume percentage of the dielectric particles in the selectively emissive layer ranges from 1% to 25%; and   the selectively emissive layer is substantially solar transparent or translucent.   
     
     
         2 . The selective radiative cooling structure of  claim 1 , wherein the structure is in the form of a sheet. 
     
     
         3 . The selective radiative cooling structure of  claim 1 , wherein the selective radiative cooling structure provides a radiative heat flux from 50 W/m 2  to 150 W/m 2  at a working temperature in the range of −100° C. to 500° C. 
     
     
         4 . The selective radiative cooling structure of  claim 1 , wherein the dielectric particles have an average size ranging from 3 μm to 15 μm. 
     
     
         5 . The selective radiative cooling structure of  claim 1 , wherein the dielectric particles are selected from the group consisting of silicon dioxide (SiO 2 ), calcium carbonate (CaCO 3 ), silicon carbide (SiC), zinc oxide (ZnO), titanium dioxide (TiO 2 ), and alumina (Al 2 O 3 ). 
     
     
         6 . The selective radiative cooling structure of  claim 1 , wherein the polymer of is selected from the group consisting of a 4-methyl-1-pentene polymer, a 4-methyl-1-pentene copolymer, polyvinyl fluoride, polyethylene terephthalate. 
     
     
         7 . The selective radiative cooling structure of  claim 1 , wherein the polymer is a copolymer of poly(4-methyl-1 pentene) with a-olefins selected from the group consisting of 1-pentene, 1-hexene and 1-octene. 
     
     
         8 . The selective radiative cooling structure of  claim 1 , wherein the selectively emissive layer has an average thickness of from 10 μm to 3 mm. 
     
     
         9 . The selective radiative cooling structure of  claim 1 , wherein the selective radiative cooling structure further comprises a protective film that is solar-transparent and weather-resistant. 
     
     
         10 . The selective radiative cooling structure of  claim 1 , wherein the selective radiative cooling structure has a solar absorptivity from 0 to 0.2 over a wavelength range of 0.3 μm to 3 μm. 
     
     
         11 . The selective radiative cooling structure of  claim 1 , further comprising a solar reflective layer in contact with the selectively emissive layer, the solar reflecting layer comprising a metal film or metal substrate, wherein the selectively emissive layer has an emissivity ranging from 0.6 to 1.0 over the wavelength range 7 μm to 13 μm and the selective radiative cooling structure has a solar reflectivity ranging from 0.8 to 1 over the wavelength range 0.3 μm to 3 μm. 
     
     
         12 . The selective radiative cooling structure of  claim 10 , wherein the metal film has an average thickness from 20 nanometers to 1000 nanometers. 
     
     
         13 . The selective radiative cooling structure of  claim 1 , wherein the dielectric particles have an average effective diameter selected from the range of 3 μm to 30 μm 
     
     
         14 . A method for removing heat from a body by selective thermal radiation, the method comprising the steps of:
 a. placing a selective radiative cooling structure according to  claim 1  in thermal communication with a surface of the body, wherein the selective emissive layer of the selective radiative cooling structure is in thermal communication with the body,   b. transferring heat from the body to the selective radiative cooling structure; and   c. radiating heat from selectively emissive layer of the selective radiative cooling structure.   
     
     
         15 . The method of  14 , wherein the body is a solar panel, a roof or window of an automobile, a roof or window of a building, or a cold storage structure for energy, food, oil or other commodity. 
     
     
         16 . The method of  claim 14 , wherein the selective radiative cooling structure further comprises a solar reflecting layer comprising a metal film or substrate and has a solar absorptivity from 0 to 0.2 over the wavelength range of 0.3 μm to 3 μm. 
     
     
         17 . The method of  claim 14 , wherein the body is a passive thermosiphon or an active channel array and wherein the heat transfer fluid circulates inside the body. 
     
     
         18 . A cold collection system comprising:
 a. a plurality of cold collection devices, each cold collection device configured to be in thermal communication with a heat transfer fluid;   b. a plurality of selective radiative cooling structures, each selective radiative cooling structure in thermal communication with the surface of one of the plurality of cold collection devices;   wherein each selective radiative cooling structure comprises a selectively emissive layer of  claim 1 .   
     
     
         19 . A method for making a selective emissive layer, the method comprising the steps of:
 a. extruding a feed material comprising a polymer, in which a plurality of dielectric particles is dispersed, through a die to form a film or sheet, wherein the polymer is characterized by an absorptivity of 0.6 to 1.0 in the range 7 μm to 13 μm; wherein the plurality of dielectric particles has an average size ranging from 3 μm to 30 μm and the volume percentage of the plurality of dielectric particles in the polymer ranges from 15 to 25%; and   b. cooling the film or sheet.