Modeling of the catalytic properties of high-temperature surface insulation in a dissociated carbon dioxide — Nitrogen mixture

A model of the heterogeneous catalysis of a dissociated carbon dioxide — nitrogen mixture on high-temperature heat-shield coatings is developed; the model takes into account nonequilibrium adsorption-desorption reactions of nitrogen and oxygen atoms and carbon dioxide molecules and their recombination in the Eley-Rideal reactions. On the basis of a comparison of the calculated heat fluxes in dissociated carbon dioxide with those measured on the VGU-4 plasma generator of the Institute for Problems in Mechanics of the RAS, the parameters of the catalysis model in question are chosen for three modern oxidant-resistant coating materials. The performances of these coatings are compared for the conditions of Mars Miniprobe entry into the Martian atmosphere. Their usability for the entry path considered is shown. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 106–116, January–February, 2000. The study was carried out with the support of the Russian Foundation for Basic Research (project No. 99-01-00259) and the “Integratisya“ Federal Program (project No. 2.1–414).     

Determination of the Effective Probabilities of Catalytic Reactions on the Surfaces of Heat Shield Materials in Dissociated Carbon Dioxide Flows

The effect of heterogeneous catalysis on the heat transfer to cold and heated surfaces in subsonic dissociated carbon dioxide jet flows is studied experimentally, using a 100 kW inductive plasma generator, and simulated numerically. The effective probabilities of the heterogeneous reactions CO + O → CO₂ and O + O → O₂ on molybdenum (T_w=300 K) and quartz (T_w=470–620 K) surfaces, the Buran heat shield tile coating (T_w = 1470—1670 K), and two oxidation-resistant carbon-carbon coating materials (T_w=1420—1840 K) are determined by comparing the experimental and calculated data on the heat fluxes at the stagnation point of models at a pressure of 0.1 atm.     

On the recombination mechanism of atomic nitrogen near a catalytic surface in a stream of dissociated air

It is shown that the heterogeneous recombination of nitrogen atoms on a catalytically active surface in a stream of dissociated air is accompanied by intense gas-phase recombination of the nitrogen in exchange reactions whose rate is determined by the rate of heterogeneous recombination of atomic oxygen.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 156–158, May–June, 1980.     

Three-dimensional chemically nonequilibrium viscous shock layer on a catalytic surface with allowance for associated heat transfer

A three-dimensional flow of dissociating air past blunt bodies is investigated in the framework of the thin viscous shock layer theory. Multicomponent diffusion and homogeneous chemical reactions, including dissociation, recombination, and exchange reactions, are taken into account. The generalized Rankine-Kugoniot conditions are specified on the shock wave and the conditions which take into account the heterogeneous catalytic reactions, on the surface of the body. The viscous shock layer equations are solved together with the heat equations inside the coating, which is carbon with a deposited thin film of SiO₂, or quartz. The case of a thermally insulated surface is also considered. The problem for the case of the motion of a body along the re-entry trajectory into Earth's atmosphere is investigated numerically. The temperature of the surface and the heat flux toward it are given as a dependence on the height (tine) of the flight for different cases of the specification of the catalytic reactions. It is shown that the difference between the heat fluxes towards the thermally insulated surface and the fluxes toward the heat-conducting surface in the neighborhood of the stagnation point is of the order of 6–12% for all the cases considered. This makes it possible to decouple the solution of the problem of heat conduction in the body.Translated fron Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 140–146, November–December, 1985.deceased     

Methods and Results of an Experimental Determination of the Catalytic Activity of Materials at High Temperatures

Methods of experimental determination of the rate constants of heterogeneous catalytic recombination of nitrogen and oxygen atoms in dissociated subsonic nitrogen and air flows generated by a high-frequency inductive plasmatron are discussed. Together with the values of the probability of heterogeneous recombination used in the literature, the rate constant of the elementary process of nitrogen atomic recombination is determined in accordance with the Langmuir-Hinshelwood mechanism.     

Increased heat transfer to a titanium surface with oxygen injection into the nonequilibrium boundary layer

The results of an experimental and numerical investigation of the heat transfer between a subsonic jet of dissociated nitrogen and a titanium surface, through which molecular oxygen is blown into the jet, are presented. It is established that in the nonequilibrium boundary layer regime the dependence of the heat flux on the injected oxygen flow rate is nonmonotonic. At a certain flow rate the heat transfer to the titanium surface reaches a maximum that considerably exceeds (by 20%) the heat transfer to an impermeable wall. The observed increase in heat transfer in the presence of injection is attributed to the interaction of the gas-phase exchange reactions and the recombination of atoms on the titanium surface, which has sharply different catalytic properties with respect to the recombination of nitrogen and oxygen atoms.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 148–155, July–August, 1991.     

Modeling of catalytic activity of an Al2O3 surface on the basis of the first principles

The adsorption, desorption, impact, and associative heterogeneous recombination rate coefficients are determined for atomic oxygen in the temperature range between 500 and 2000 K on the basis of quantum chemical data on the energy of interaction of atomic and molecular oxygen with the clusters that model an α-Al₂0₃ surface. These coefficients are used to calculate the heterogeneous recombination probabilities and the heat fluxes to the surface under the conditions similar to those of the MESOX facility.     

Effect of surface catalytic activity on nonequilibrium heat transfer in a subsonic jet of dissociated nitrogen

The present paper investigates experimentally and numerically the effect of the heterogeneous recombination of atoms on the heat transfer of models in a subsonic jet of dissociated nitrogen for the conditions of an experiment in the VGU-2 plasma generator and determines the effective probabilities of the heterogeneous recombination of nitrogen atoms for a number of materials at high temperatures.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 166–172, May–June, 1985.     

Diffusion separation of chemical elements on a catalytic surface

An asymptotic expansion of the solution, for large Schmidt numbers, of the system of equations of a chemically nonequilibrium multicomponent boundary layer on the catalytic surface of a blunt body [1] is used to obtain expressions for the diffusion fluxes of the reaction products and chemical elements and the heat flux as functions of the gradients of the reaction product concentrations, chemical element concentrations and enthalpy across the boundary layer. It is shown that when the body is exposed to a supersonic air flow, the diffusion separation of the chemical element oxygen depends importantly on the atom concentration at the outer edge of the boundary layer and the nature of the homogeneous and heterogeneous catalytic reactions. If the surface promotes the rapid recombination of oxygen atoms and is chemically neutral with respect to nitrogen atoms, then an excess of the chemical element oxygen is formed on the body. Otherwise we get an enhanced concentration of the element nitrogen. As distinct from the case of an ideally catalytic wall [2–4], on a surface possessing the property of catalytic selectivity the diffusion separation of chemical elements takes place even when only atoms are present at the outer edge of the boundary layer. On a chemically neutral surface diffusion separation may be caused by homogeneous recombination reactions between oxygen and nitrogen atoms if their rate constants are essentially different.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 115–121, July–August, 1988.     

Nonequilibrium hypersonic flow of carbon dioxide gas over blunt bodies

The Navier-Stokes equations are used to investigate hypersonic flow of carbon dioxide gas over blunt bodies with allowance for nonequilibrium development of chemical reactions and vibrational relaxation of the CO₂ molecules. The problem is solved by the method of stabilization by means of an implicit difference scheme that includes the use of Newton's iterative process. The results are given of calculations of the flow field, the convective heat flux, and the frictional stresses on the surface of blunt cones with spherical noses. The influence of admixtures on the flow field and the heat fluxes is investigated. The results of the calculations are compared with the locally self-similar solution for the neighborhood of the front stagnation point.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 199–202, September–October, 1979.     

Determination of heat fluxes in the neighborhood of a double curvature stagnation point in a flow of dissociating gas of arbitrary chemical composition

Numerical solutions are obtained for the equations of a uniform compressible boundary layer with variable physical properties in the vicinity of a stagnation point with different principal curvatures in the presence of an injected gas with the same properties as the incident flow. The results of the numerical solutions are approximated for the heat flux in the form of a relation that depends on the variation of the product of viscosity and density across the boundary layer and on the ratio of the principal radii of curvature.Using the concepts of effective diffusion coefficients in a multicomponent boundary layer, previously introduced by the author in [1], and the generalized analogy between heat and mass transfer in the presence of injection, together with the numerical solutions obtained, it is always possible, even without additional solutions of the boundary-layer equations, to derive final formulas for the heat fluxes in a flow of dissociating gas of arbitrary chemical composition, provided that we make the fundamental assumption that all recombination reactions take place at the surface.By way of example, formulas are given for the heat transfer to the surface of a body from dissociating air, regarded as a five-component mixture of the gases O, N, NO, O₂, N₂, and from a dissociating mixture of carbon dioxide and molecular nitrogen of arbitrary composition, regarded as an eleven-component mixture of the gases O, N, C, NO, C₂, O₂, N₂, CO, CN, C₃, CO₂.In the process of obtaining and analyzing these solutions it was found that, in computing the heat flux, a multicomponent mixture can be replaced with an effective binary mixture with a single diffusion coefficient only when the former can be divided into two groups of components with different (but similar) diffusion properties. In this case the concentrations of one group at the surface must be zero, while the diffusion flows of the second group at the surface are expressible, using the laws of mass conservation of the chemical elements, in terms of the diffusion flows of the first. Then the single effective diffusion coefficient is the binary diffusion coefficient D(A,M), where A relates to one group of components and M to the other.In view of the small amount of NO(c(NO) < 0.05), the diffusion transport of energy in dissociated air maybe described with the aid of a single binary diffusion coefficient D(A, M)(A=O, N, M=O₂, N₂, NO). However even in the case of complete dissociation into O and C atoms at the outer edge of the boundary layer, the diffusion transport of energy in dissociated carbon dioxide can not be described accurately enough by means of a model of a binary mixture with a single diffusion coefficient, since the diffusion properties of the O and C atoms are distinctly different.     

Analysis of the heterogeneous recombination of oxygen atoms on aluminum oxide by methods of quantum mechanics and classical dynamics

On the basis of the density-functional theory, cluster models of the adsorption of oxygen atoms on aluminum oxide are constructed and the corresponding potential-energy surface is calculated. Quantum-mechanical calculations showed that it is necessary to take into account the angular dependence of the potential-energy surface and the relaxation of the surface monolayers. Using this surface in molecular dynamics calculations made it possible to obtain the probabilities of the heterogeneous recombination of oxygen atoms on the α-Al₂O₃ surface, which are in good agreement with experimental data. The calculations performed substantially decrease the amount of experimental investigations necessary reliably to describe the heterogeneous catalysis on promising reusable heat shield coatings for analyzing heat transfer during spacecraft entry into the atmosphere.     

Formulas for the heat and diffusion fluxes to a catalytic surface in a chemically nonequilibrium multicomponent boundary layer

On the basis of an asymptotic expansion of the solution of the equations of a multicomponent chemically nonequilibrium boundary layer for large Schmidt numbers, formulas are obtained for the heat flux and the diffusion fluxes of the reaction products and chemical elements on a surface with arbitrary catalytic activity. The results are compared with well-known analytic and numerical solutions. The comparison reveals the high accuracy of the formulas proposed. The results of calculating the diffusional separation of the mixture due to the selectivity of the catalytic properties of the surface with respect to recombination of oxygen and nitrogen atoms are presented. Values of the reduction of the convective heat fluxes due to the catalytic properties of the surface are obtained over a wide range of conditions in the free stream.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 171–176, March–April, 1996.     

Gas dynamic ozone generator

The formation of ozone when partially dissociated oxygen flows out of a supersonic nozzle has been investigated experimentally and theoretically. The supersonic flow of a chemically reacting gas mixture containing excess O atoms is calculated in the one-dimensional approximation for a class of plane wedge-shaped nozzles. It is shown that for initial gas pressures ahead of the nozzle inlet of about 10 atm and a temperatureT ₀=1000 K in nozzles with a total vertex angle of 30°C and a throat dimensionh.=1 mm it is possible to obtain an ozone concentration of about 1%, which is comparable with ordinary ozonizers, while the output of the device is two to three orders greater. Experiments on a shock tube fitted with a nozzle to measure the absorption of UV radiation by oxygen recombining in the nozzle under highly nonoptimal conditions revealed the presence in the flow of ozone molecules formed as a result of O+O₂ recombination.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 139–148, November–December, 1994.     

Model of the physico-chemical kinetics behind the front of a very intense shock wave in air

A model of the physico-chemical kinetics of the reactions taking place behind the front of an intense shock wave propagating in air with a speed of 9–14 km/s is proposed. The problem of describing the chemical reactions, namely, molecular dissociation and exchange reactions involving vibrationally excited molecules in the absence of vibrational equilibrium, is solved. The vital role of the vibrational excitation delay in the dissociation of oxygen and nitrogen is established. The rate of the exchange reaction between nitrogen molecules and oxygen atoms in the shock wave depends only slightly on the vibrational excitation level. It is demonstrated that the rate constants for thermally nonequilibrium dissociation reactions can be represented within the framework of the one-temperature approximation at constant vibrational temperatures of the dissociating species satisfying quasi-stationary conditions.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 169–182, March–April, 1995.     

Catalytic properties of a copper transducer for determining flow parameters in a high-frequency induction plasmatron

The rate coefficients of the elementary stages of the complete system of heterogeneous catalytic recombination of dissociated oxygen on a copper oxide surface are determined on the basis of quantum-mechanics calculations within the framework of cluster models. The coefficients are used to calculate the dependence of the effective coefficient of heterogeneous catalytic recombination of oxygen atoms on the temperature and the partial pressure on a wide range of surface conditions. It is established that it can considerably vary depending on these conditions.     

Simulation of oxygen atom adsorption on an Al<Subscript>2</Subscript>O<Subscript>3</Subscript> surface by the density functional method

Several cluster models of oxygen atom adsorption on an Al₂O₃ surface are constructed on the basis of the density functional method. The performed quantum mechanical computations allow one to reveal a number of important features of the potential energy surface to describe the heterogeneous catalytic processes with the use of molecular dynamics methods. The heterogeneous recombination of oxygen atoms is simulated according to the Eley-Rideal mechanism. It is shown that the potential energy surface should be used with consideration of the internal relaxation of surface monolayers to correctly describe the process under study.     

Some physical aspects of radiative and convective heat transfer in the case of nonself-similar blowing on a plate

Heat shielding by blowing has been fairly fully studied in the neighborhood of the stagnation point of a body in a stream [1–3], but for other flow regions the investigation has barely begun [4]. It has been found that the influence of blowing on the radiative and convective fluxes and the influence of radiation on the convection on the side wall can be very different from what is obtained for the flow conditions at the stagnation point. The present paper is a study of the radiative and convective heat transfer on a plate in a H₂ + He stream for constant and self-similar blowing of carbon vapor in the form of C, C₂, and C₃.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 28–35, January–February, 1981.     

Investigation of heat transfer on models in subsonic jets of an induction plasmatron

The results are given of an investigation of the flow parameters in an induction plasmatron and of heat transfer on water-cooled models in subsonic jets of dissociated air in the range of pressures p = 5·10³–1.0·10⁵ N/m². The obtained experimental data confirm the well-known theoretical conclusion that the catalytic activity of the surface influences the heat fluxes at low pressures when the boundary layer flow is nonequilibrium. The problem of the flow of a subsonic jet of a viscous heat-conducting gas past a model of cylindrical shape with flat end has been solved numerically. The experimental and calculated data are compared.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza., No. 6, pp. 129–135, November–December, 1983.We are very grateful to Yu, K. Rulev and V. M. Mysova for assistance in the experiment.     

Component desorption effect on the material catalyticity in high-temperature multicomponent gases

The distinctive features of the formation of the catalyticity of materials with respect to atom recombination on the material surface are investigated for mixtures of different high-temperature gases under conditions of hypersonic atmospheric flight or bench setups. It is shown that in general the catalyticity constants (heterogenous recombination probabilities) of individual components determined experimentally in dissociated flows of “pure” gases are improperly used for calculating the heat fluxes to material surfaces in multicomponent gas flows, owing to differences in the occupation of the surface by atoms in pure gases and mixtures. This effect must be taken into account in interpreting the experimental data which so far have been the only source of information on material catalyticity in gas mixtures. Otherwise, the results of calculations of the heat transfer to hypersonic flight vehicles could turn out to be invalid. Examples of the possible effect of ignoring this factor on the calculated heat fluxes are presented.