Abstract
Simplified thermochemical ablation models are developed for three ceramic heat-shield materials, potentially useful as high-performa nce re-entry nosetips. The models are based on phase equilibrium at the ablating surface and on the simplified film-coefficient approach for unity Lewis-Semenov number. Limited test data from the Avco Model 500 arc are compared with the predictions based on equilibrium thermochemistry, and discrepancies are discussed and explained. The thermochemical models are used to compare the ablative performance of these materials in a typical high-performance nosetip environment, and the most attractive materials, from this standpoint, are identified. Nomenclature cp = specific heat C = constant defined by Eq. (35) D = diameter of test specimen / — fraction of silicon vaporized AF/ = standard molal free energy of formation of specie / at surface temperature h = heat-transfer coefficient based on enthalpy driving force h0 = heat-transfer coefficient in the absence of mass transfer He = recovery enthalpy, BTU/lbm Hs = enthalpy of heat-shield material at surface temperature,
Published Version
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