Numerically enhancing daytime radiative cooling performance of random dielectric microsphere coatings by hollow structures

Dielectric microsphere coatings for passive daytime radiative cooling (PDRC) are gaining attention owing to their low cost and potential for mass production. The cooling performance could be further enhanced to effectively reflect solar radiation and emit thermal radiation to the cold sky by designing microspheres suitable for PDRC applications. Hollow dielectric structures were numerically designed to enhance the PDRC performance of dielectric microsphere coatings. The maximum solar reflectance ((R) over bar (solar) = 0.96) was obtained with a fill rate f = 0.6, outer radius r(out) = 0.5 mu m, core-shell rate phi = r(in)/r(out) = 0.3, thickness t = 300 mu m, and thermal infrared emittance e LWIR = 0.90. Furthermore, by controlling the multisize sphere distribution within f = 0.1 to 0.5, the cooling performance at t = 300 mu m was enhanced to R solar = 0.98, e LWIR = 0.95, and a net cooling power of 77 W/m(2) was achieved at a temperature of 25 degrees C, which was similar to 38% higher than that achieved with the single-size sphere coating (f = 0.3) and similar to 64% higher than that of the solid SiO2 sphere coating (f = 0). These results indicate that hollow structures can effectively enhance the cooling performance of dielectric microsphere coatings by increasing the number of interfaces between the air and dielectric materials. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

Automated summary

Dielectric microsphere coatings with hollow structures can enhance the performance of passive daytime radiative cooling by increasing the number of interfaces between air and dielectric materials. Controlling the distribution of multisize spheres within a certain range can effectively improve the cooling performance.