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, and a cold collection system comprising a plurality of the polymer-based selective radiative cooling structures.
1. A cold collection system comprising:
a plurality of cold collection devices, each cold collection device configured to be in thermal communication with a heat transfer fluid;
a plurality of selective radiative cooling structures, each selective radiative cooling structure in thermal communication with a surface of one of the plurality of cold collection devices and each of the plurality of selective radiative cooling structures comprising:
a selectively emissive layer comprising a polymer, and a plurality of dielectric particles dispersed in the polymer, the volume percentage of the plurality of dielectric particles in the selectively emissive layer ranging from 1% to 25% and the plurality of dielectric particles characterized by an average size ranging from 3 μm to 30 μm; and
a reflective layer that is a silver film characterized by an average thickness from 20 nanometers to 300 nanometers, wherein the selectively emissive layer of each selective radiative cooling structure is provided on the reflective layer of each selective radiative cooling structure;
wherein the selectively emissive layer of each selective radiative cooling structure is characterized by an average emissivity ranging from 0.6 to 1.0 over the wavelength range of 7 μm to 13 μm, and the selectively emissive layer of each selective radiative cooling structure has a transmissivity of 0.7 to 1 over a solar wavelength range of 0.3 μm to 3 μm;
wherein the polymer of the selectively emissive layer of each selective radiative cooling structure 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; and
wherein the plurality of dielectric particles of the selectively emissive layer of each selective radiative cooling structure comprises silicon dioxide (SiO 2 ); and
wherein the selectively emissive layer of each selective radiative cooling device is in thermal communication with one of the plurality of cold collection devices.
2. The cold collection system of claim 1 further comprising a heat exchanger, wherein the heat transfer fluid is in fluidic communication with the heat exchanger.
3. The cold collection system of claim 1 , wherein the cold collection device is a passive thermosiphon or active channel array.
4. The cold collection system of claim 1 , wherein each selective radiative cooling structure is in the form of a sheet.
5. The cold collection system of claim 1 , wherein each selective radiative cooling structure provides a radiative heat flux from 250 W/m 2 to 150 W/m 2 at a working temperature of 15° C.
6. The cold collection system of claim 1 , wherein the dielectric particles of the selectively emissive layer of each selective radiative cooling structure are characterized by an average size ranging from 4 μm to 10 μm.
7. The cold collection system of claim 1 , wherein the selectively emissive layer of each selective radiative cooling structure is characterized by an average thickness from 10 μm to 3 mm.
8. The cold collection system of claim 1 , wherein each selective radiative cooling structure further comprises a protective film that is solar transparent and weather-resistant.
9. The cold collection system of claim 1 , wherein each selective radiative cooling structure is characterized by a solar absorptivity from 0 to 0.2 over a wavelength range of 0.3 μm to 3 μm.
10. The cold collection system of claim 1 , wherein in each selective radiative cooling structure, a barrier layer is provided between the selectively emissive layer of each selective radiative cooling structure and the reflective layer of each selective radiative cooling structure.
11. The cold collection system of claim 1 , wherein the polymer of each selective radiative cooling structure and the plurality of dielectric particles of each selective radiative cooling structure are mixed as a uniform blend.
12. The cold collection system of claim 1 , wherein the polymer of the selectively emissive layer of each selective radiative cooling structure 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.