Novel Semi-Empirical Model for Finite Rate Catalysis with Application to PM1000 Material

Abstract

DOI: 10.2514/1.44552 A simplified model for heterogeneous catalysis is presented. A theoretical expression of the recombination coefficienthasbeenobtainedbymeansofananalogywithgas-phasekinetics,wherebydesorptionisassumedsimilar to final product formation following decomposition of the activated compound. The constants of the model are defined by fitting experimental data. The method devised is particularly useful when detailed physical modeling approaches are unrealizable, namely when material characteristics are unknown. This model has been applied to PM1000, the material planned for the ESA EXPERT capsule external skin. The expression of the recombination coefficient has been interpolated using the experimental data provided by the Centre National de la Recherche Scientifique in France and the von Karman Institute in Belgium, implemented in the Centro Italiano Ricerche Aerospaziali computational fluid dynamics code, and tested for typical reentry conditions. Its application to the EXPERT capsule reentry problem shows that it appears to work well and is promising. Results confirm the importance of realistically modeling catalytic recombination on thermal protection systems, both in terms of wall heat flux and chemical composition of the airstream near the surface. In particular, the heat flux predicted is much lower than in the case of fully catalytic surface, indicating that, at the points of the EXPERT trajectory chosen, PM1000 seems to have poor catalytic activity.