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"Analyse
and Prediction of Catalytic Properties of Heat Shield Coatings by Molecular Dynamic
Modeling." V.L. Kovalev (MSU) Abstract: To calculate the heat loads and
predict the life-time of the reusable heat shield it is necessary to have
basic information on the processes of thermo chemical interaction between
dissociated air and heat shield materials. The most important processes are
catalytic atom recombination. The heat fluxes to surfaces with different
catalytic properties can differ by several times. Despite the fact that since
the fifties it has been well known that heterogeneous atom recombination
significantly affects heat transfer at hypersonic flight velocities, the
mechanisms and rates of the processes which determine the interaction between
the gas and the surface have been much less closely studied than the kinetics
and the homogeneous chemical reaction rates.
The complexity of the problem of determining the catalytic properties
of the surface is associated with the fact that there are no direct methods
of measuring the recombination coefficients and chemical energy accommodation.
Molecular dynamics models are
useful to understand the surface chemical reactions from a molecular point of
view. Molecular dynamics simulations predict some quantities that cannot be
easily measured in experimental observations, such as: state-to-state surface
coefficients and their dependence upon the internal energy content of
reactive molecule; translational and internal energy distributions of the
product states; energy exchanged between the surface and the chemical system
reaction mechanism and reaction pathways. In this report “MD Trajectory”
software complex was developed to investigate mechanisms of heterogeneous
catalytic processes. “MD Trajectory” was tested on supercomputer clusters of Using molecular dynamics approach
the elementary catalytic heterogeneous reactions on SiO2 or SiC
based coatings have been studied in details and all its significant
characteristics including both recombination and accommodation coefficients,
distributions of molecules formed during recombination over vibrational and
rotational states have been determined. Good agreements between our results
and calculations or experimental results of other authors were revealed. It
was revealed that silicon carbide surface will be heated more effective due
to oxygen recombination than SiO2 one because chemical energy
accommodation coefficient for this surface is higher than last one on the
full range of collision energy. |
