Chemical Reactions and Thermal Nonequilibrium on Silica Surfaces

Frühauf, H.-H.; Messerschmid, Ernst

doi:10.1007/978-94-009-0267-1_12

Cited by 8 publications

(6 citation statements)

References 4 publications

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“…The existence of c w maximum (¼ 6 £ 10 ¡ 3 ) points out the change of the recombination mechanism at T w ¼ 1470 K: The c w drop with T w increasing is a result of oxygen atoms desorption rate growth at a surface temperature above 1470 K. This result is in qualitative agreement with theoretical models already developed for atomic oxygen recombination on silica-based surfaces. 7,35,36 Therefore, on the basis of the data in Fig. 8, we can recommend the following approximationfor the catalyticef ciency of the silicabased surface in the dissociated carbon dioxide ow: c w = 2.58 £ 10 ¡ 2 exp ¡ 2.08 £ 10 3 T w 390 · T w · 1470 K 1.13 £ 10 ¡ 4 exp 5.79 £ 10 3 T w 1470 · T w · 1670 K (16) Note that recombination of the C atoms contributes to the heat ux at the enthalpiesabove 35 MJ/kg.…”

Section: Resultsmentioning

confidence: 98%

Study of Quartz Surface Catalycity in Dissociated Carbon Dioxide Subsonic Flows

Колесников

Pershin

Васильевский

et al. 2000

Journal of Spacecraft and Rockets

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The stagnation point heat transfer from subsonic dissociated carbon dioxide ows to quartz and cooled metallic surfaces has been measured by calorimetry and studied numerically. The aerothermal tests were performed using the 100-kW IPG-4 inductive plasmatron at 10 4 Pa pressure in the enthalpy range 14.4-38.5 MJ/kg. The numerical simulation included the computations of the carbon dioxide inductively coupled plasma torch, of the subsonic reacting ows around a cylindrical model, and in a nonequilibrium boundary layer. The model of catalysis based on the Eley-Rideal mechanism, in which adsorption of oxygen atoms predominates over other species adsorption, is proved to be suf cient to explain the heat transfer data. Silver is found to be the best catalyst and molybdenum a poor one. The ef ciencies of the catalytic recombination reactions O + O ! ! O 2 and CO + O ! ! CO 2 on quartz and silica-based thermal protection surface have been determined and combined in the surface temperature range 390-1670 K by comparing the experimental and numerical heat transfer data. The catalytic ef ciencies of quartz-and silica-based surfaces in dissociated carbon dioxide appeared to be quite similar to the ones obtained in dissociated pure oxygen. The maximum of an average catalytic ef ciency for both reactions on silica has been revealed at the surface temperature 1470 K (°w ¼ 6 £ 10 ¡ 3 ). Adsorption and desorption of oxygen atoms play the key roles in catalysis on silica-based surfaces in dissociated carbon dioxide ows. For the prediction of the aeroheating silica-based thermal-protection surfaces during entry into the Martian atmosphere, an approximation of the catalytic ef ciency as a function of surface temperature in the range 390-1670 K is given. Nomenclature b = thickness of the heat reception wall of a quartz calorimeter, mm C = mass fraction D = diameter of the plasmatron discharge channel, mm F = frequency of rf generator, MHz f = dimensionless stream function G = mass ow rate through discharge channel, g/s h = gas enthalpy, MJ/kg I = dimensionless mass diffusion ux J = mass diffusion ux, kg/(m 2 s) K w = catalytic recombination rate constant, m/s k = Boltzmann constant M = Mach number m = dimensionless molecular weight of the gas mixture m i = molecular weight of species i , kg N ap = anode power of the rf generator, kW N pl = power input in plasma, kW Pr = Prandtl number p = pressure, Pa q = stagnation point heat ux, W/cm 2 q c = heat loss density measured by water-cooled calorimeter, W/cm 2 Re = Reynolds number R m = model radius, m r = normal cylindrical coordinate related to the model surface, m S = site for the surface-adhered atom Sc = Schmidt number T = temperature, K U = longitudinal velocity component in the cylindrical coordinate system, m/s u = dimensionless velocity gradient V = ow velocity along central line, m/s y 0 = longitudinal cylindrical coordinate related to the model surface, m a = dimensionless external ow vorticity c = surface catalytic ef ciency D = dimensionless boundary-layer thickness d = boundar...

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Section: Resultsmentioning

confidence: 98%

Study of Quartz Surface Catalycity in Dissociated Carbon Dioxide Subsonic Flows

Колесников

Pershin

Васильевский

et al. 2000

Journal of Spacecraft and Rockets

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“…This type of model is often used for parametric studies seeking to bound catalytic effects [37], but lacks physics-based kinetic formulations that describe intermediate catalytic behavior under transient thermal and flow environments. A more attractive approach for including the NO surface formation in CFD computations is with a finite-rate surface chemistry model as implemented by Kurotaki [5] and others [1][2][3][4]6,7], a model that incorporates kinetic mechanisms like adsorption, thermal desorption, Eley-Rideal recombination, and LangmuirHinschelwood recombination. Unfortunately, these models contain large numbers of numerical parameters that must be chosen by theory and/or adjusted to reproduce experiment data.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…This choice is partly a matter of computational convenience and partly because of the lack of experimental information on the importance of the NO formation pathway. More recent modeling efforts have introduced finite-rate kinetic models to better capture the physics of surface catalytic reactions [1][2][3][4][5][6][7]. In at least one case, the inclusion of NO surface formation in a finite-rate surface chemistry model seems to improve agreement between aerothermal heating computations and measured flight data [5].…”

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confidence: 99%

Nitric Oxide Production from Surface Recombination of Oxygen and Nitrogen Atoms

Pejaković¹,

Marschall²,

Duan³

et al. 2008

Journal of Thermophysics and Heat Transfer

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Experimental results are presented that support the surface-catalyzed production of nitric oxide from the recombination of oxygen and nitrogen atoms on quartz. The experiments employ two-photon laser-induced fluorescence detection of atomic oxygen and atomic nitrogen to characterize changes in gas-phase atom concentrations as the ratio of O to N atoms is varied at the opening of a diffusion-tube side-arm reactor. The measurements verify a correlation between decreased O-atom loss and enhanced N-atom loss in N 2 =N=O mixtures. Computational simulations of the side-arm reactor with a multispecies reaction-diffusion model strengthen the case for NO surface formation, reproducing observed changes in O-and N-atom concentration profiles with varying O/N ratios at the side-arm entrance when surface-catalyzed NO production is included in the boundary conditions. Nomenclature c = concentration or molar density, mol m 3 D = diffusion coefficient, m 2 s 1 F = volumetric flow rate, sccm f s;r = branching fraction of reactant s into product r j = diffusive mass flux, kg m 2 s 1 k B = Boltzmann's constant 1:381 10 23 J K 1 L = side-arm length, m M = molar mass, kg mol 1 N Avro = Avogadro's number, 6:022 10 23 mol 1 P = pressure, Pa R = side-arm radius, m R = universal gas constant, 8:314 J mol 1 K 1 r = radial side-arm coordinate, m T = temperature, K v = bulk flow speed, m s 1 v = average thermal speed, m s 1 w = gas-phase production rate, kg m 3 s 1 w w = surface production rate, kg m 2 s 1 x = mole fraction z = axial side-arm coordinate, m = loss probability 1;1 rs = collision integral, m 2 = viscosity, Pa s = mass density, kg m 3 = diffusion velocity, m s 1 ! s = weighting factor, Eq. (4) Subscripts O, O 2 , N, N 2 , NO = species s = species index r = species index or radial direction w = wall z = axial direction

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“…Although models of this type are often used for parametric studies seeking to bound catalytic effects [28], a more attractive approach for including the NO surface formation in CFD computations is with a finite-rate surface chemistry model as implemented by Kurotaki [1] and others [29][30][31][32][33][34] (i.e., a model that incorporates kinetic mechanisms like adsorption, thermal desorption, Eley-Rideal recombination, and Langmuir-Hinschelwood recombination). Unfortunately, these models contain large numbers of numerical parameters that must be chosen by theory and/or adjusted to reproduce experiments.…”

Section: B Simulation Resultsmentioning

confidence: 99%

Direct Detection of NO Produced by High-Temperature Surface-Catalyzed Atom Recombination

Pejaković¹,

Marschall²,

Duan³

et al. 2010

Journal of Thermophysics and Heat Transfer

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The surface-catalytic recombination of oxygen and nitrogen atoms to form nitric oxide was confirmed by the direct detection of product NO molecules, using single-photon laser-induced fluorescence spectroscopy. Experiments were performed from room temperature to 1200 K in a quartz diffusion-tube sidearm reactor enclosed in a hightemperature tube furnace. Atomic nitrogen was generated using a microwave discharge, and atomic oxygen was produced via the rapid gas-phase titration reaction N NO ! O N 2 . The use of isotopically labeled titration gases 15 N 16 O and 15 N 18 O allowed for the unambiguous identification of nitric oxide produced by the O N surface reaction. The absolute number densities of surface-produced NO were determined from separate calibration experiments using 14 N 16 O. Observed variations of the NO number density with temperature and varying O=N atomic ratios at the sidearm entrance are generally consistent with the predictions of a simple reaction-diffusion model of the sidearm reactor that includes surface-catalyzed NO production as a species boundary condition. Nomenclature c = concentration or molar density, mol m 3 D = diffusion coefficient, m 2 s 1 E = activation energy, J mol 1 f s;r = branching fraction of reactant s into product r j = diffusive mass flux, kg m 2 s 1 k i = rate coefficient for reaction i, cm 3 molecule 1 s 1 or cm 6 molecule 2 s 2 L = sidearm length, m M = molar mass, kg mol 1 P = pressure, Pa R = sidearm radius, m R = universal gas constant, 8:314 J mol 1 K 1 r = radial sidearm coordinate, m T = temperature, K v = average thermal speed, m s 1 w = gas-phase production rate, kg m 3 s 1 w w = surface production rate, kg m 2 s 1 x = mole fraction z = axial sidearm coordinate, m = loss probability = mass density, kg m 3 = diffusion velocity, m s 1 Subscripts O, O 2 , N, N 2 , NO = species r = species index or radial direction s = species index w = wall z = axial direction

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Chemical Reactions and Thermal Nonequilibrium on Silica Surfaces

Cited by 8 publications

References 4 publications

Study of Quartz Surface Catalycity in Dissociated Carbon Dioxide Subsonic Flows

Study of Quartz Surface Catalycity in Dissociated Carbon Dioxide Subsonic Flows

Nitric Oxide Production from Surface Recombination of Oxygen and Nitrogen Atoms

Direct Detection of NO Produced by High-Temperature Surface-Catalyzed Atom Recombination

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