Research On Regulation Mechanism Of Spectral Radiative Properties Of Transparent Thermal Insulation Aerogels

As a clean renewable energy source,solar energy has the advantages of abundant reserves,wide distribution and easy access,and it plays an important role in constructing an efficient energy system and realizing green and low-carbon energy development.Solar energy can be utilized by solar thermal conversion,photovoltaic conversion,and photochemical conversion.Among them,solar thermal conversion is currently the most applied and the most mature technology.Depending on the target solar wavelength,solar thermal conversion can be divided into full-spectrum solar utilization and spectral selective solar utilization.The full-spectrum solar utilization absorbs the solar radiation in the entire spectral range and converts it into thermal energy.To improve the efficiency of solar thermal conversion,transparent insulation materials are required to reduce heat loss;The spectral selective solar utilization absorbs the solar radiation in a specific wavelength range and achieves the solar thermal conversion,which requires the use of transparent insulation materials to achieve spectral filtering.All of the above problems require to regulate the radiative characteristics of transparent insulation materials,design and optimize the spectral radiative properties of transparent insulation materials,and realize the full spectrum/spectral selective absorption of solar energy by transparent insulation materials,which is of great significance to improve the solar energy utilization.In this paper,we conducted an investigation on regulating the radiative properties of transparent thermal insulation materials for various solar energy utilization occasions,and the specific research content and conclusions are as follows:(1)The radiative properties of gold/silver nanocylinders and nanospheroids were investigated by Discrete Dipole Approximation and T-matrix methods.The excitation law of plasmon resonance in nanoparticles was clarified,and a nanoparticles doping scheme of plasmonic aerogels was designed.The full-spectrum solar absorption and spectral selective absorption performance were simulated by the Monte Carlo method with different particle morphologies,aspect ratios,and doping concentrations.It is found that hybrid doped silver nanocylinders and indium tin oxide nanoparticles achieved excellent solar absorption efficiency in the full solar spectrum,which provids an important guideline for designing efficient solar desalination devices.Doping silver nanocylinders(AR=0.15)and nanospheroids(AR=0.3)achieved the selective absorption of near-infrared and green light respectively,which provides theoretical basis for designing transparent anti-/deicing surfaces and spectral filtering membranes for enhancing photosynthesis in greenhouses.The study aims to analyze the influencing factors of plasmon resonance effect,and reveal the regulation mechanism of radiative properties of nanoparticles,which provides a new perspective for achieving selective absorption of solar energy.(2)Based on the complex refractive index of transparent conductive indium tin oxide(ITO)obtained from the Drude model,the radiative properties of ITO nanocylinders were investigated,and the regulation law of ITO nanocylindrical radiative properties was revealed.A transparent thermal insulation aerogel composite formed by doping ITO nanocylinders was proposed and optimized,a heat transfer model by coupling the transparent thermal insulation aerogel composiote with a concentrated solar power plant was established to investigate the hightemperature thermal insulation performance.The transparent thermal insulation aerogel composite can reduce the high-temperature radiative thermal loss significantly,which can reach a higher oprtation temperature with a smaller solar concentration compared to pure silica aerogel.The study shows that the ITO nanocylinders doped aerogel has excellent hightemperature thermal insulation performance,which demonstrates that the transparent thermal insulation aerogel composite will play an important role in enhancing high-temperature solar thermal conversion.(3)The 3D porous SiO2/Al2O3 core/shell aerogel microstructure was reproduced by an improved Diffusion Limited Cluster Aggregation.The cross-scale radiative transfer properties of the core/shell aerogel were investigated by combining Discrete Dipoles Approximate and Monte Carlo methods,and the relationship between the microstructure and radiative transfer properties was obtained.A high thermally stability core/shell aerogel structure with high solar transmission,excellent infrared radiation suppression,and extremely low effective thermal conductivity was achieved by optimizing the structure design.The study indicates that reproducing the microstructure of aerogel is an effective way to tune the radiative properties,which provides significant guidance for developing thermally stable aerogel suitable for the next-generation high-temperature concentrated solar thermal plants.