Graphite Ablation Chemistry Nonequilibrium Effects
AEROSPACE CORP EL SEGUNDO CA VEHICLE ENGINEERING DIV
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This implications of the assumption of local solid-gas phase equilibrium for subliming carbon species for graphite ablation calculations in an air environment is investigated. The equilibrium assumption is eliminated by considering the Knudsen-Langmuir equation at the interface for each carbon specie. Calculated equilibrium and nonequilibrium results are compared for a very wide range of flight and ground test environments. The nonequilibrium mass addition parameter is always less than the equilibrium value and the non- equilibrium wall temperature is always larger for a given environment. Calculations made to determine the convective heat flux required to reach an incipient melt temperature of 3800 K indicate that the required flux determined from an equilibrium calculation can be too high by as much as 200-300 percent for stagnation enthalpies less than 5000 Btulb. Calculations for superorbital reentry conditions show large differences in the mass addition parameter B when the convective heating rate is low and the external radiation heating level is relatively high. Similar large differences in B could be simulated in an existing ground test facility if the reported external radiation heating level could be increased. Such an experiment would provide data to test the validity of present convective heating rate blowing corrections in a combined heating environment.
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