Cooling the coating to a radiation spot colors

Cooling buildings, vehicles and other ground objects and data centers are the key challenges we face today. Cooling typically requires a lot of energy, because a lot of power consumed based on a compressor cooler. Using the reflection of sunlight and heat radiation surface sustainable way of cooling an object in the sun. However, these white or silver surface can not meet the demand for color. To solve this problem, people of color to study the radiation cooler (CRC). CRC may selectively display the desired portion of the visible spectrum absorbed by a color, and other solar wavelengths, especially in the past to SWIR is reflected. However, the existing CRC or performance range are restricted. Thus, in a highly scalable manner while achieving color and radiation cooling performance remains a challenge. Recently, Columbia University Yang Yuan , Southern Yu in \” Science Advance [ 123] \”describes a two-layer coating of one color and radiative cooling may be achieved simultaneously on. The light scattering layer coating comprises a non-absorbing visible light-absorbing layer and the top layer. Top reflector to maximize the absorption of visible wavelength suitable to display a specific color, and the bottom layer is the near SWIR (NSWIR) light to reduce solar radiation. Accordingly, the temperature of the two-layer coating in strong sunlight low 3.0 ° to 15.6 ° C than the commercial single layer coating of the same color, and can obtain a higher reflectance NSWIR (0.1 to 0.51). These properties indicate that the double layer coating can be designed simple, inexpensive and scalable way to achieve efficient radiative cooling and color.

Figure 1. double CRCs NSWIR enhanced reflection. (A) while maintaining the visible spectrum reflectance of NSWIR increase the reflectivity. (B) light and thermal radiation and the interaction between the schematic design may be coated bilayer. (C) a double (left) and monolayer (right) applied to the photo on a plastic substrate. (D) four pairs of different colors P (VdF-HFP) bilayer and monolayer coating visible (left) and NSWIR photographs (right).double layer coating having a thick absorbent layer and non-light scattering thin colored top. Since the top layer is thin (FIG. 2D) and the coloring agent of light NSWIRWeak scattering, the light transmittance will NSWIR wavelength, along the optical path enters the bottom of the short without substantial absorption. Sunlight scattered into the non-absorbent underlayer, NSWIR backscattered light will strongly to the top, return almost unhindered free space, resulting in higher R

NSWIR . In addition, a conventional thin top layer having the same color of the target single colorant concentration and composition. Although much thinner than the single layer coating, it still has a sufficient thickness to ensure that the target is strongly absorbed by the complementary color of visible light, while other wavelengths were scattered sunlight itself or the underlying reflector.

Figure 2. bilayer design principles. (A and B) show the sun and monolayer (A) and a double interaction of the coating (B). Spectrum of the complex refractive index of the polymer (C) comprises a selective black dye. A schematic view of (D) 🙁 left set of three analog) sunlight scattering porous polymer, (middle) refractive index (C), a single-layer porous polymer staining (right) at the bottom is a scattering medium, the top of a monolayer film It doubles. (E) (D) of three analog reflectance structure.This paper studies the ground floor are two types of scattering sunlight. One is a thickness of 500μm having about 50% porous P (VdF-HFP) thick layer, which comprises interconnected micropores and nanopores (FIG. 3A), resulting in an efficient backscattered sunlight. Another standard commercial radiation cooling 250μm nonporous TiO2-based white coatings. Compared with commercial single layer coating, the two layer design showed almost the same color, but was significantly higher RNSWIR. As shown in FIG 3 (C to F), each of the visible spectrum of single and double color trends closely matched, resulting in similar CIE x and y chromaticity values ​​and a smaller difference in brightness (FIG. 3B). However, in NSWIR based on double porous P (VdF-HFP) is higher than the reflectivity of TiO2 based on the bilayer.

Figure 3. Structural and optical properties of the double layer coating is cooled. (A) Red porous P (VdF-HFP) optical microscope bilayer, bilayer and monolayer coatings – TiO2 (a) (scale bar, 20 [mu] m) and scanning electron microscopy (lower) (scale, 5 microns) image. Black, chroma (B) CIE 1931 color space display blue, red and yellow coatings cooling. (C toF) are black (C), the blue reflectance (D), red (E), yellow (F) cooling the coating spectrum.in FIG. 3 by the double and single layer Sample (C to F) exposed to direct sunlight (Fig 4, A and B) can be demonstrated in a double-implemented method may lead to better enhance RNSWIR daytime cooling performance. In the extreme case (sample black), because larger RNSWIR contrast, at about 1025 W m

-2 ^{of the solar radiation, the porous P (VdF-HFP) and the ratio of TiO2-based double monolayer and low temperature 15.6 ° C 13.2 ° C (FIG. 4C).}

Figure 4. Experimental cool outdoor temperature color paint. (A and B) a schematic view of apparatus for testing and photographs temperature in the sun. (C to F) are black (C), blue (D), red (E), yellow (F) cooling the coating in an outdoor test detailed solar intensity (half of the y-axis) and temperature (y-axis lower half part of data.These results indicate that the design layer coating, in particular based on a porous P (VdF-HFP) design, the building can be reduced, and cost of the automobile air conditioning and the temperature of other objects on the ground. From a practical point of view, the two-layer coating may satisfy the cooling performance through a simple manufacturing process, while meeting the aesthetic requirements of color. The full text link: https: //advances.sciencemag.org/content/6/17/eaaz5413