Radiative Heat Transfer in Silica Aerogel

Abstract

At ambient temperatures evacuated aerogel exhibits a very low apparent thermal conductivity (λ ≅ 8…10 mW/(m K)). With rising temperatures, however, the heat transfer is increasing very rapidly. This is mainly due to the weak absorption region in the near infrared (ir) which transmits more and more of the thermal radiation when the spectrum is shifted towards shorter wavelengths. The dominance of the radiative transport over conduction and convection at high temperatures can also be observed in glass melts [1]. In addition to the radiative heat transport in evacuated aerogel the solid conduction via the fragile skeleton has to be considered. It is possible to determine the amount of solid conductivity λ_sc if the radiative contribution and the total heat flux are precisely known. This, however, implies a detailed experimental and theoretical investigation of the radiative heat transfer as well as the precise calorimetric measurement of the total thermal transport in aerogel.