Effects of ordered hierarchically porous structure on methane reforming performance in solar foam reactor

Biomimetic hierarchical structure for enhancing concentrated solar energy converting and utilizing efficiency

Concentrated solar technology has the problems of local overheating, inadequate light absorption, and insufficient diffusion of solar irradiation energy flow. In this study, the idea of using biomimetic hierarchical structure is proposed to solve these problems through radiation regulating and photon managing, thereby enhancing the conversion and utilization efficiency of concentrated solar energy. The performance of uniform porous structure and biomimetic hierarchical structure are comparatively investigated. The geometrical parameters (diameters, ratio, and filling factor) of the biomimetic hierarchical structure are investigated and optimized by finite-difference time-domain (FDTD) method combined with particle swarm optimization algorithm. The results indicate that the biomimetic hierarchical structure can enhance the effective light absorption and energy flow diffusion efficiency of concentrated solar energy, an increasing pore size is better for the biomimetic hierarchical structure than a decreasing pore size, and the feature sizes which serve as the boundary between large and small pores are found. For the effective light absorption, the biomimetic hierarchical structure has an enhancement of 3.4%, and for the energy flow diffusion efficiency, this structure has an enhancement of over 25%, compared with the uniform porous structure. This research can provide general and valuable guidance for enhancing solar energy utilizing efficiency of high-temperature solar thermochemical reactors, solar cells, and photocatalytic carriers, based on the biomimetic hierarchical structure.

Wrinkled surface microstructure for enhancing the infrared spectral performance of radiative cooling

Radiative cooling is a passive cooling method that does not consume additional energy and has broad application prospects. In recent studies, the surface microstructure was found to have a significant influence on improving the emissivity in infrared spectra for radiative cooling. Accordingly, in this paper, an innovative wrinkled surface microstructure without any periodicity is proposed for enhancing the infrared spectral performance of radiative cooling. The effects of the height and number of wrinkles as well as the radius and volume fraction of particles on the infrared spectral performance of radiative cooling are investigated. The radiative cooling performances of the plane, pyramid, moth-eye, and wrinkled microstructures are comparatively investigated using the finite-difference time-domain (FDTD) method. The results show that the mean emissivity of innovative radiative cooling films with the wrinkled surface microstructure reaches 99.58% in the "atmospheric window" wavelength range. The mean emissivity of the wrinkled microstructure is improved by 19%, 22.16%, and 8.41% over those of the plane, pyramid, and moth-eye microstructures, respectively. This indicates that the wrinkled microstructure exhibits a better performance for radiative cooling than single periodic surface microstructures. Furthermore, the wrinkled microstructure has no periodicity so it has low production cost, which makes it possible to replace other periodic surface microstructures.