Heat and Mass Transfer in Thermal Protection Composite Materials upon High Temperature Loading

Heat and mass transfer in thermal protection composite materials, used as heat protection of the structural elements of hypersonic aircrafts, is simulated in this work. Two phases arise upon high-temperature loading of the composite materials: one, unaffected by the decomposition of the binder of the composite material, and the other, a porous residue in which phase transitions are completed. These two phases are separated by a narrow zone of the binder decomposition, limited by moving boundaries of the beginning and end of the phase transformations with gas formation and a variable density of the composite materials. Analytical solutions of the problems of heat and mass transfer are obtained for the first two phases; a transcendental equation for determining the coordinates and velocity of the pyrolysis zone is derived based on these solutions and the balance of heat flows in this zone. The found mass velocity of the pyrolysis zone made it possible to determine the mass generation rate, density, and stagnation pressure of the pyrolysis gases in the decomposition zone, as well as the mass filtration rate in the porous coke residue. The validity of the proposed mathematical model is confirmed by many numerical experiments. The results of some experiments are given as functions of time, temperature, the thermal characteristics, the mass and linear velocities of the pyrolysis zone, the density and stagnation pressure of gases in this area, and the pressure distribution and the mass filtration rate in the resulting porous residue.