Study On Fast Preparation And Building Energy Eiffciency Application Of Aerogels For Super Thermal Insulations

Silica aerogels have attracted increasing attentions in thermal insulationapplications in building and industrial areas owing to their unique characteristics suchas lightweight, high porosity, super-low thermal conductivity and super hydrophobic.This paper focuses on the fast preparation technique and the thermal insulationapplications in building glazing systems of SiO₂aerogels. A fast and low-costpreparation technique of SiO₂aerogels insulations is established based on one stepsolvent exchange and surface modification and atmospheric drying. The effectmechanisms of the preparation parameters on the hydrophobic, thermal conductivity,and mechanical strength of the SiO₂aerogels are explored by using both the singleand the orthogonal experimental designs so as to optimize the preparation parameters.Based on the as-prepared SiO₂aerogels, a newly aerogel glazing systems is developedfor building energy efficiency.By using single factor experimental design, the effect of preparation parametersof SiO₂aerogels during the sol-gel, solvent exchange and surface modification wereexplored. The rough ranges of the preparation parameters were accordingly defined.The orthogonal experiments with four parameters and three levels were carried out tooptimize the four key parameters （viz., hydrolysis time, aging fluid volume ratio,modification time, and ratio of modification solvents）. The optimized preparationparameters could be obtained as12h for hydrolysis time,1:4for ratio of aging fluidvolume,10%of modification solvents, and72h for modification time. Under theoptimized preparation conditions, the as-prepared SiO₂aerogels had the super-lowthermal conductivity of0.018W/（m·K） and super-high contact angle of153.6°.Moreover, the preparation period of SiO₂aerogels could be shorten to half of thetraditional preparation period.The infrared transmission coefficients of the as-prepared SiO₂aerogels wereexperimentally measured by using the instrument of architectural glass visibletransmittance. The results showed that the visible light transmittance and shading coefficient of the SiO₂aerogels were64.2%and0.87, respectively. The as-preparedSiO₂aerogels were filled in two pieces of clear glass to form a type of SiO₂aerogelglazing system. The results showed that the visible light transmittance and the directsolar transmittance of the aerogel glazing system were43.2%and40%, respectively.The shading coefficients and heat transfer coefficients of the aerogel glazing systemwere0.66and1.2W/（m2·K）. This indicates that newly developed aerogel glazingsystem had super-low heat transfer coefficients and good visual transmittance.The cooling and heating loads of a model building assembling traditionalbuilding glass and newly developed aerogel glazing system were calculated by usingVirtual Environment （VE） codes. The results showed that the heat transfer load ofbuilding glass assembling the newly developed aerogel glazing system could bereduced by75%,63%and58%, respectively, compared to the clear glass, Low-Eglass and hollow double-layer glass. In cold climate zones heating dominated, theannual building energy saving rate could be up to18%.