Multi-layer graded doping in silica aerogel insulation with temperature gradient

•Sizes of doping opacifiers and fibers in silica aerogel are optimized.•Optimal doping amount is obtained to reduce the effective thermal conductivity.•Multi-layer graded doping of opacifiers and fibers in aerogel is presented.•Experimental measurement of aerogel back temperature validates the predictions. Radiative heat transfer at high temperature deteriorates the insulating capability of silica aerogel due to its poor extinction characteristics for wavelength below 8μm. Both the infrared opacifier doping and fiber doping can reduce the heat transfer and improve insulating capability of silica aerogel efficiently at high temperature. We determine the optimal temperature-dependent size for typical opacifiers and silica fibers by combining the spectral extinction coefficient with blackbody radiation. The optimal temperature-dependent doping amount is obtained by minimizing the effective thermal conductivity. Based on the obtained temperature-dependent optimal parameters and the graded temperature distribution in silica aerogel, four solutions of multi-layer graded doping are presented and the insulating capability is improved effectively. The measured back temperature curves of doped silica aerogel in the experiment qualitatively verify the optimization predictions.