Effect of embedded polydisperse glass microspheres on radiative cooling of a coating

Radiative cooling, as a passive cooling method, is an effective way to save energy and reduce emissions by dissipating heat into space through the “sky window,” without consuming any additional energy. The actual particles in the radiative-cooling coating constitute a particle cloud with non-uniform size distribution and the cooling effect is greatly affected by the spectral reflectance of the actual substrate. Herein, the radiative transfer of actual SiO ₂ particles doped with a radiative-cooling coating was initially studied. Monte Carlo ray-tracing method, combined with Mie theory, was used to analyze the influence of particle size, volume fraction of particles, coating thickness, and different substrate reflectances on the spectral radiative characteristics of the radiative-cooling coating. The particles size distribution and spectral substrate reflectance were considered. The numerical results show that the maximum spectral reflectance difference between a coating with a uniform-size-distribution particle cloud and a coating with a non-uniform-size-distribution particle cloud can reach 27.3%. Furthermore, the influence of particle parameters and reflectance of the substrate on the radiative characteristics of the radiative-cooling coating is mainly concentrated in the 10–12 μm band. At 8–10 μm and 12–13 μm, the radiative-cooling coating emissivity varies little with the change of particle parameters and the reflectance of substrate, which is induced by the strong absorption of SiO ₂ particles.