An approximate methodology to simulate combined conduction-radiation heat transfer for multi-layer insulator

Abstract

A quasi-analytical methodology was developed to model combined conductionradiation heat transfer through the thickness of a re ective multi-layer insulator. This methodology was validated based on the experimental result. It can be applied to the initial design of high-temperature multi-layer insulators. Traditionally, radiation thermal conductivity approximation was employed for the initial stages of design. Despite the acceptable accuracy of this approach in steady state cases, it yields some unacceptable errors when thermal load is transient. It was shown that the older version of this methodology could not predict maximum temperature and time of occurrences by acceptable margins. The developed model originated from the radiation thermal conductivity approximation. Unlike the primitive one, the developed model shows acceptable performance in transient cases. This model was developed with emphasis on thermal emittance through the thickness of the insulator. It can predict the maximum temperature of a structure and its occurrence time with an error less than 4%.

Thermal Insulation Performance of Aerogel Nano-Porous Materials: Characterization and Test Methods

“…Aerogel nano-porous materials have strong permeability to near-infrared radiation with wavelengths of 3–8 μm at high temperature, which leads to the poor shielding ability of aerogel at high temperature, and the thermal conductivity of aerogel increases significantly with the increase in temperature [ 24 ]. For this reason, compared to the heat conduction heating and convective heating methods for measuring nano-porous materials, the infrared heating method has “extra” energy penetrating into the aerogels, resulting in higher measurement results.…”

“…For aerogel nano-porous materials, the radiation heat imported from the outside or emitted by the solid skeleton in the nano-porous material will be absorbed and scattered by the solid phase material when it passes through the pores or skeleton in the nano-porous material [ 22 , 23 ]. It must be mentioned that aerogel has strong permeability to near-infrared radiation with wavelengths of 3–8 μm at high temperature, which leads to the poor shielding ability of aerogel at high temperature, and the thermal conductivity of aerogel increases significantly with the increase in temperature [ 24 ].…”