Modeling of Catalytic Reactions on Silica Surfaces with Consideration of Slip Effects

A detailed surface chemistry model is presented for the reactions of N 2, O2, NO, N, and O on a silica surface. The model distinguishes adsorption, desorption, and recombination reactions according to the Eley‐ Rideal and Langmuir ‐ Hinshelwood mechanisms as well as dissociative adsorption reactions of the molecular species. The model parameters are adjusted by comparison of predicted recombination coefe cients for N and O with experimentally determined recombination coefe cients. For the calculation of surface heating rates of re-entry vehicles, the model is implemented into a multiple-temperature Navier ‐ Stokes code and coupled with a slip model to take into account rarefaction effects at high altitudes. Computational results obtained with the surface chemistry model for Shuttle-equivalent hyperboloids are compared to Shuttle e ight data. Nomenclature c¯ = average particle velocity E = activation energy F = energy e ux f = velocity distribution function G = particle energy H = enthalpy h = Planck constant I = moment of inertia K = equilibrium constant k = rate coefe cient or Boltzmann constant l = vibrational level m = particle mass n = particles per unit surface area P = steric factor Q = partition function s = sticking coefe cient T = temperature v = particle velocity Z = particle e ux per unit surface area = accommodation coefe cient = chemical energy accommodation coefe cient = recombination coefe cient = characteristic vibrational temperature = symmetry number = mole fraction C = reaction rate per unit surface area