Radiative cooling structures and systems
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.
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, the volume percentage of the dielectric particles in the selectively emissive layer selected from the range of 1% to 25% and the particles characterized by an average size ranging from 3 μm to 30 μm;
a reflective layer comprising a metal film or metal substrate, wherein the selectively emissive layer is provided on the reflective layer;
wherein the selective radiative cooling structure is characterized by an average emissivity ranging from 0.6 to 1.0 over the wavelength range 7 μm to 13 μm;
wherein the selectively emissive layer has a transmissivity of 0.7 to 1 over a solar wavelength range of 0.3 μm to 3 μm;
wherein the polymer is selected from the group consisting of polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), a 4-methyl-1-pentene polymer, a 4-methyl-1-pentene copolymer and polyvinyl fluoride;
wherein the dielectric particles comprise silicon dioxide (SiO 2 ); and
wherein the reflective layer is a silver film characterized by an average thickness from 20 nanometers to 300 nanometers.
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 of 15° C.
4. The selective radiative cooling structure of claim 1 , wherein the dielectric particles are characterized by an average size ranging from 4 μm to 10 μm.
5. The selective radiative cooling structure of claim 1 , wherein the selectively emissive layer is characterized by an average thickness from 10 μm to 3 mm.
6. The selective radiative cooling structure of claim 1 , wherein the selective radiative cooling structure further comprises a solar transparent, water-proof or weather resistant protective film that is a solar transparent and weather-resistant polymer.
7. The selective radiative cooling structure of claim 1 , wherein a barrier layer or a protective layer is provided between said selectively emissive layer and said reflective layer.
8. The selective radiative cooling structure of claim 1 , wherein the particles are characterized by an average size of 8 μm.
9. The selective radiative cooling structure of claim 1 , wherein the polymer and dielectric particles are mixed as a uniform blend.
10. The selective radiative cooling structure of claim 1 , wherein the selectively emissive layer is characterized by an average thickness from 5 μm to 500 μm.
11. The selective radiative cooling structure of claim 1 , wherein the volume percentage of the dielectric particles in the selectively emissive layer selected from the range of 5% to 15%.
12. The selective radiative cooling structure of claim 1 , wherein the polymer is selected from the group consisting of polyethylene terephthalate (PET), a 4-methyl-1-pentene polymer, and a 4-methyl-1-pentene copolymer.
13. The selective radiative cooling structure of claim 1 , wherein the polymer is selected from the group consisting of a 4-methyl-1-pentene polymer, and a 4-methyl-1-pentene copolymer.
14. The selective radiative cooling structure of claim 1 , wherein the polymer is a 4-methyl-1-pentene copolymer copolymer.
15. The selective radiative cooling structure of claim 1 , wherein the polymer is a copolymer of poly(4-methyl-1 pentene) with α-olefins selected from the group consisting of 1-pentene, 1-hexene and 1-octene.
16. The selective radiative cooling structure of claim 15 , wherein the dielectric particles are silica.
17. The selective radiative cooling structure of claim 16 , wherein the selectively emissive layer is characterized by an average thickness from 5 μm to 500 μm.
18. The selective radiative cooling structure of claim 17 , wherein the dielectric particles are characterized by an average size ranging from 4 μm to 10 μm.
19. The selective radiative cooling structure of claim 18 , wherein the volume percentage of the dielectric particles in the selectively emissive layer selected from the range of 5% to 15%.
20. The selective radiative cooling structure of claim 19 , wherein the polymer and dielectric particles are mixed as a uniform blend.