Effect of Medium Radiation on Thermal Conductivity Measurement of Aerogels Using Steady-State Heating Method

Radiative heat transfer in aerogels (semi-transparent materials) acts as a participating medium, causing notable errors in conventional steady-state thermal conductivity measurements. Coupled conduction–radiation heat transfer is numerically simulated to examine the influence of variations in the heating plate-specimen interface emissivity on thermal conductivity measurements, and the simulation results are experimentally validated using test systems with differing interface emissivities. The results show that the effect of interface emissivity on effective thermal conductivity is more obvious under high temperatures and low extinction coefficients. When the average temperature is 1273 K, the emissivity decreases from 1 to 0.2, and the effective thermal conductivity with extinction coefficients of 3.5 m⁻¹ and 3500 m⁻¹ decreases by 76.1% and 24.1%, respectively. Experimental results show that when the hot surface temperature is 873 K, the cold surface temperature differences in different test systems can reach 30 K. The experimental results have the same trend as the steady-state simulation results, which verifies the accuracy of the numerical simulations. Quantitative analysis of the steady-state heating measurement results demonstrates the effect of medium radiation in semi-transparent materials on the obtained results. The findings contribute to a more accurate characterization of silica aerogel composites and provide new insights into the influence of radiative heat transfer on thermal conductivity evaluation in semi-transparent aerogel materials, which is important for the development and application of aerogel-based thermal insulation systems.