Influences of gas permeation with adsorption effect on the transient thermal insulation performance of silica aerogel at pressure and temperature differences

Silica aerogel is a thermal protective material for an outer space launch under aerodynamic heating, significant temperature difference, and pressure gradient conditions. This paper proposes a gas permeation model by considering the gas adsorption effect for silica aerogel under pressure differences. The gas (N-2) adsorption behavior of silica aerogel is simulated by the grand canonical Monte Carlo method. This simulation provides the concentration of the adsorbate gas layer and the average thickness of adsorbate gas in the nanopore. An unsteady-state heat transfer model within silica aerogel, coupling with the acquired gas diffusion effect, heat conduction, and thermal radiation, is developed to study the thermal insulation performance. The gas permeation with the gas adsorption inside silica aerogel exerts a prominent influence on the dynamic temperature response of the hot surface. At the temperature of 77-90 K, the gas adsorption has a remarkable impact on the gas permeation within silica aerogel, which would finally affect the energy migration. The order of the coefficient changes from 10(-14) to 10(-10) m(2). In contrast, the adsorption effect is negligible at the temperature of 298-1300 K. When the gas diffusion and heat transfer directions are opposite, gas diffusion will impede heat transfer, and thus the thermal insulation performance will be improved up to 88.94% and 25.65% at unsteady- and steady-state, respectively.