Preparation Of High Transparent SiO₂ Aerogel And Its Application In Dish Solar Thermal Power Generation System

Transparent SiO₂ aerogel has promising foreground in the utilization of solar energy photothermal conversion because of its transparency and thermal insulation.However,the properties of transparent SiO₂ aerogel are highly related to its preparation.Meanwhile,the transparency and thermal insulation performance analysis of transparent SiO₂ aerogel is also the basis for its application in the field of solar energy high-temperature photothermal conversion.In this dissertation,a supercritical CO₂ extraction drying process was developed for the preparation of highly transparent SiO₂ aerogel,and the effects of high temperature were studied by characterization methods.Al-doped Zn O（AZO）was used as the dopant of transparent SiO₂ aerogel to study the effects of doping on the transmission of solar radiation and infrared thermal radiation,and a wavelength-dependent radiation model of transparent SiO₂ aerogel was established to investigate its photothermal conversion performance.To improve the thermal performance of dish solar thermal power system at high temperature,a cavity receiver enhanced with transparent SiO₂ aerogel was proposed,and its photothermal conversion performance under different conditions were simulated.Finally,a dish Stirling thermal power generation system based on lunar regolith thermal energy storage was proposed to achieve the circadian continuous energy supply for future lunar base,and the energy supply characteristics of the system were investigated using finite-time thermodynamic method.The main conclusions are as follows:（1）The supercritical CO₂ extraction drying process can achieve the rapid cleaning of SiO₂ wet gel and shorten the preparation period to prepare highly transparent SiO₂ aerogel.The solar spectral weighted transmittance of the transparent SiO₂ aerogel after high-temperature treatment can reach 93.8%.However,high-temperature treatment increases the transmission of SiO₂ aerogel to infrared thermal radiation and decreases the thermal insulation performance of the aerogel.The high temperature of 900℃will significantly reduce the nanoporous characteristics of the aerogel.（2）The transmittance analysis of aerogel shows that the transmittance of transparent SiO₂ aerogel in the short waveband range（250～750 nm）is mainly affected by its scattering,whereas the transmittance in the long waveband range is mainly affected by its absorption.The wavelength-dependent radiation model based on the radiation characteristics of transparent SiO₂ aerogel can be used to analyze the photothermal conversion performance of the aerogel.The results show that nano AZO doping can enhance the absorption of transparent SiO₂ aerogel in the infrared thermal radiation,but reduce the photothermal conversion performance of aerogel because of the decrease of solar radiation transmission.（3）Transparent SiO₂ aerogel can be used to reduce heat loss of a cavity receiver.The simulation results show that a 10 mm-thickness transparent SiO₂ aerogel can reduce the heat loss of the aerogel cavity receiver by 22.3%and increase the thermal efficiency by 4.2%at an operating temperature of 1000 K.The improvement of the thermal performance of the aerogel on the cavity receiver will increase with the increase of the operating temperature,but decrease with the increase of the intercepted solar radiation energy.（4）The simulation study of the dish Stirling thermal power system based on lunar regolith thermal energy storage shows that the output power and efficiency of the system gradually decrease whether in lunar day or lunar night.The average output power during the lunar day and night are 10.7 k W and 7.1 k W,respectively.The system can achieve a high energy efficiency of 40.39%,which is mainly owing to the full utilization of lunar in-situ resources such as solar radiation,lunar regolith and the space cold source on the moon.