Heterogeneous catalysis effects in Mars entry problem Valery L. Kovalev Moscow State University, Russia ERICE-SICILY:1-7 AUGUST 2005

Schematic of flow field with catalytic recombination, excited state production and quenching.

Calculated flux to MESUR spacecraft with various catalytic boundary conditions.

THREE TYPES OF SILICONIZED COATING MATERIALS Coating I : the glassy coating of the > orbiter tile heat shield based on the SiO2 - B2O3 - SiB4 system Coating II: an oxidant — resistant carbonaceous coating based on alumina borosilicate glass with a MoSi2 admixture Coating III: a coating made up of a new composite material based on the Hf — Si — С — В system.

Nonequilibrium jet from plasmatron flowing around butt-end probe (Mach number)

Experimental regimes Parameters Regimes Te, К Vs, m/s 47,3 76,1 105,6 118,0 145,0 164,0 q fc W, Wt/cm2 4 6,4 74,4 103,7 130,0 175,0 208,0 N, kWt  p, Pa 10,5 17,5 24,5 26,2 33,75 38,8

CATALYTIC MECHANISM chemical adsorption and desorption atoms 1. O + S V  O S Eley — Riddel reactions 2. O S + O  S V + O 2 3. O S +CO  S V + CO 2 physical adsorption and desorption 4. О + F V  O f, diffusion to the nearest chemisorptions site 5. O f + S V  О S + F V Lengmuir — Hinshelwood recombination 6. O f + O S  O 2 + F V + S V, 7. O S + O S  O S V

MASS RATES OF SPECIES FORMATION IN HETEROGENEOUS CATALYTIC REACTIONS

Elementary rate coefficients

DETERMINATION OF THE MODEL PARAMETERS SIMPLIFYING ASSUMPTION  ads = const (1); Q (A-S) = Q S (2) VALUES OF THE MODEL PARAMETERS (Reaction 1-3) Curve a 1 ER a 3 ER a 4 ER 5 5 7 7 E O ad E CO a d E 1 ER E 3 ER E 4 ER a b , с d , Coating II Coating III The r.m.s. deviation of the calculated heat fluxes from the measured ones did net exceed 5 %.

Temperature dependence of the heat fluxes to coating I at stagnation point

Temperature dependence of the effective coefficients of heterogeneous recombination for coating I

Temperature dependence of the effective coefficients of heterogeneous recombination for coating III

Experimental regimes Parameters Regimes Te, К Vs, m/s 47,3 76,1 105,6 118,0 145,0 164,0 q fc W, Wt/cm2 4 6,4 74,4 103,7 130,0 175,0 208,0 N, kWt  p, Pa 10,5 17,5 24,5 26,2 33,75 38,8

Table. 1 NReactionAEQRef. 1 O + S V  O S 0, [1] 2.O S + O  S V + O 2 0, _ _,, _ 3 O S +CO  S V + CO 2 0, _ _,, _ 4 О + F V  O f 0, [2,3] 5 O f + S V  О S + F V 0,053 0 _ _,, _ 6 O f + O S  O 2 + F V + S V 0,053 0 _ _,, _ 7 O S + O S  O S V 0,02125_[4] 1,0 500 _ [5] Reactions with physical adsorption atoms and model parameters

Heat fluxes on the surface taking into account processes with physical adsorbed atoms

Temperature dependences of effective recombination probability of oxygen atoms

Heat fluxes on the surface taking into account the recombination of carbon atoms

Mini-probe forebode configuration and computational domain Mole fraction CO2 distribution Temperature distribution. H = km, (sizes on Figure are indicated in cm) Free stream entry conditions H, km V , m/s P , kg/m 3 T , К         

Flight altitude dependence of the heat fluxes to different coatings at the stagnation point for the Mars miniprobe

MARS miniprobe surface equilibrium temperature along the trajectory for different coatings

Configuration of space vehicle MSRO

The distribution of heat fluxes across the frontal surface of MSRO S, м q w, Вт/см Рис. 2. Влияние гетерогенных каталитических процессов на тепловые потоки к теплозащитному экрану

The distribution of heat fluxes across the bottom surface of MSRO

Surface equilibrium temperature across the bottom surface of MSRO

Effect of physical adsorption for the bottom surface of MSRO

Summary On the basis of the Langmuir layer theory, a model of the interaction of dissociated carbon dioxide mixture with a catalytic surface is developed. This model takes into account both chemical and physical adsorbed atoms. Comparison of the calculated heat fluxes with measured ones show that the model is able to predict heat-transfer in a wide temperature range, from 300 up to 2000 K. The performances of the ciliconized coatings are compared for the entry conditions of Mars Miniprobe and MSRO. The results obtained show they could be used in the thermal insulation system of the vehicle. It is established, in particular, that using the glassy coating of the > orbiter tile heat shield would result in a 2.5-fold reduction in the maximum heat flux to the vehicle nose along the entire trajectory as compared with an ideal catalytic surface and in a reduction of the maximum surface temperature could be 500 K.

Literature 1.Kovalev V.L., Afonina N.E., Gromov V.G. Catalysis Modeling for Thermal Protection Systems of Vehicles Entering into Martian Atmosphere. AIAA Paper Kim Y.C., Boudart M. Recombination of O, N, and H on Silica: Kinetics and Mechanism, Langmuir Gordiets B.F., Ferreira C.M. Self-consistent modelling of volume and surface processes in air plasma. AIAA Paper Daiss A., Fruhauf H.H., Messerschmid E.W. Modeling of catalytic reactions on silica surfaces with consideration of slip effects. J. Thermophysics and Heat Transfer , N 3, Nasuti F., Barbato M., Bnmo C. Material — dependent catalytic recombination modeling for hypersonic flows. J. Thermophysics and Heat Transfer N Bykova N.G., Vasil’evskii S.A., Gordeev A.N., Kolesnikov A.F., Pershin I.S., Yakushin M.I. Determination of the Effective Probabilities of Catalytic Reactions on the Surface of Heat Shield Materials in Dissociated Carbon Dioxide Flows, Fluid Dynamics, Vol.32(1997), No.6, pp Kolesnikov A.F., Pershin I.S., Vaail'evskii S.A., Jakushin M.I. Study of quartz surface catalycity in dissociated carbon dioxide subsonic flows. AIAA Paper

Flight altitude dependence of the heat fluxes to coating I at the stagnation point for Mars Miniprobe

Heat fluxes on the surface with the Langmuir-Hinshelwood recombination