Theoretical and numerical predictions of the thermal conductivity of thermal protection systems

The present work evaluates the effective thermal conductivity of an ablative composite in the state of virgin material and in three different paths of degradation. The material is assumed to undergo ablation with formation of void pores and with formation of char and void pores. The one dimensional effective thermal conductivity is evaluated theoretically by the solution of heat conduction under two extreme assumptions, i.e. parallel isotherms and parallel heat fluxes. The paper presents the theoretical model applied to an elementary cubic cell of the composite material made of two crossed fibres and matrix. A numerical simulation is carried out to compare numerical results with the theoretical ones for different values of the filler volume fraction.