Numerical Studies on Spectrally Selective Characteristics and Heat Transfer Mechanism of PMMA/SiO ₂ Radiative Cooling Film

As an important solution to the global shortage of fresh water, the spectrally selective radiative cooling film can provide a potential method for harvesting all-day freshwater. In this work, the spectrally selective radiative characteristics of a PMMA/SiO2 radiative cooling film are numerically investigated by the finite‑difference time-domain (FDTD) method, and the effect of particle size, filling rate, and particle distribution on transmissivity and emissivity is discussed. In addition, the electric field distribution of the PMMA/SiO2 radiative cooling film is further analyzed to disclose the radiative transfer mechanism. The simulation results show that for 1–1.2 μm SiO2 particle size, the transmissivity values of the radiative cooling film remain relatively high due to weak scattering. The emissivity values exhibit an obvious increase with filling rate because the addition of SiO2 particles accelerates the formation of electric dipole resonance and enhances the absorption ability. Compared with the uniformly arranged SiO2 particles, the randomly arranged SiO2 particles show more stable emissivity, and the corresponding emissivity in the 8–13 μm wavelength range is 0.951. The net cooling power of the optimized PMMA/SiO2 can reach 110.2 W/m2 at the film temperature equaling to the ambient temperature. Moreover, with the increase in the non-radiative heat transfer coefficient, the enhanced convective exchange suppresses the radiative cooling effect.