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¯solar = 0.96) was obtained with a fill rate f = 0.6, outer radius rout = 0.5 μm, core–shell rate φ = rin / rout = 0.3, thickness t = 300 μm, and thermal infrared emittance ε¯LWIR = 0.90. Furthermore, by controlling the multisize sphere distribution within φ = 0.1 to 0.5, the cooling performance at t = 300 μm was enhanced to R¯solar = 0.98, ε¯LWIR = 0.95, and a net cooling power of 77 W / m2 was achieved at a temperature of 25°C, which was ∼38 % higher than that achieved with the single-size sphere coating (φ = 0.3) and ∼64 % higher than that of the solid SiO2 sphere coating (φ = 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.

中文翻译：

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空心结构随机介电微球涂层日间辐射冷却性能的数值增强

用于被动日间辐射冷却 (PDRC) 的介电微球涂层因其低成本和大规模生产的潜力而受到关注。通过设计适用于 PDRC 应用的微球，可以进一步增强冷却性能，以有效反射太阳辐射并向寒冷的天空发射热辐射。中空介电结构经过数值设计以提高介电微球涂层的 PDRC 性能。最大太阳反射率 (R¯solar = 0.96) 是在填充率 f = 0.6、外半径 rout = 0.5 μm、核壳率 φ = rin / rout = 0.3、厚度 t = 300 μm 和热红外发射率时获得的ε¯LWIR = 0.90。此外，通过将多尺寸球体分布控制在 φ = 0.1 到 0.5 内，t = 300 μm 处的冷却性能提高到 R¯solar = 0.98，ε¯LWIR = 0.95，并且在 25°C 的温度下实现了 77 W / m2 的净冷却功​​率，这比单尺寸球涂层（φ = 0.3）实现的高约 38%，比单尺寸球涂层高约 64%。固体 SiO2 球涂层 (φ = 0)。这些结果表明，中空结构可以通过增加空气和介电材料之间的界面数量来有效提高介电微球涂层的冷却性能。