Modeling heat transfer with micro-scale natural convection in fibrous insulation

Fibrous thermal insulation materials are vastly employed in the thermal protection system of recoverable space vehicles. The accurate determination of their apparent thermal conductivity allows for an adequate sizing of the thermal protection system of space vehicles, with effects on the weight, structural strength, manufacture and launch costs. This property is strongly dependent on the pressure of the gas within the porous. The objective of this work was to improve the accuracy of a well-established model for estimation of the apparent thermal conductivity of fibrous insulation materials filled with gas at various pressures, which presents some increasing discrepancy as the pressure rises. After a sensitivity analysis in every term of the current model, some modifications are tested and proposed. A micro-scale convection term is modeled and included in the modified model. The results of both versions of the model are compared with experimental data, with the modified version presenting better agreement than the original model at higher pressures.