Comparison of Surface Chemical Kinetic Models for Ablative Reentry of Graphite

A general formulation for surface chemical reactions is used with a finite element heat conduction code to compare computations of the ablated mass flux from carbon bodies experiencing conditions representative of Earth reentry. Several credible models for the surface chemical kinetics are exercised with the formulation and are compared both to each other and to test data obtained by the Passive Nosetip Technology program in the mid-1970s. Sublimation of C 5 and C 7 is shown to be a concern for surface temperatures greater than about 3900 K. The best match between measurements and the calculations is obtained with surface chemical models that use the usual CO formation reactions and the sublimation of C 1 -C 3 but that also include CN formation and the sublimation of C 5 and C 7 . For surface temperatures above 3500 K and for similar assumptions for the equilibrium vapor pressure and evaporation coefficients of the sublimated species, the net reaction rate approach and the surface site occupation approach give similar ablated mass fluxes.