The radiative cooling efficiency of silica sphere embedded polymethylpentene (TPX) systems

The silica sphere embedded hybrid system is a promising emitter for radiative cooling in construction applications. Optimization of its cooling performance requires a thorough understanding of how the fabrication parameters influence its cooling performance. The objective of this study was to explore the influence of the silica sphere radius, sphere volume fraction, and layer thickness on a material's optical properties and cooling efficiency through theoretical prediction. Using OptiFDTD and Mie theory, the optical property of eight different silica sphere radii, five different silica sphere volume fractions, and five different silica-TPX layer thicknesses were simulated and analyzed. A well-validated thermal model predicted the cooling power of these scenarios under various climatic inputs. These inputs covered the common range of the related parameters in most middle and low latitude areas. The 0.3 mu m and 0.5 mu m radii had higher emissivity in the atmospheric window and higher cooling power under various climatic conditions. Emissivity in the atmospheric window and other infrared wavelengths increased as the silica sphere volume fraction or silica-TPX layer thickness increased. The best cooling performance was balanced between high emissivity in the 8-13 mu m range and low emissivity in other infrared ranges.