Study of Quartz Surface Catalycity in Dissociated Carbon Dioxide Subsonic Flows

Abstract

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...

Dissociation of CO2 molecules in microwave plasma

“…In order to predict the behavior of the materials at the entry of space vehicles to the Mars or Venus atmospheres, extensive studies on the treatment of suitable materials with carbon dioxide plasma at elevated temperatures should be performed on Earth. Most experiments were performed in special high-frequency plasma reactors producing subsonic flow of carbon dioxide while some experiments were also performed in microwave (MW) plasma reactor as in our case [3][4][5]. Sepka et al [5] have used MW source and experiments were performed in the side-arm diffusion tube which was used to study surface catalycity according to Smith diffusion method (sink of reactant species on the tube walls as a function of axial location along the side-arm tube).…”

Survey of European and Major ISC Facilities for Supporting Mars and Sample Return Mission Aerothermodynamics and Tests Required for Thermal Protection System and Dynamic Stability

“…The plasma Hall accelerator of HMTI is able to test heatproof materials and is working with CO 2 , but there is no available information about its technical features for CO 2 . Ablation tests and catalysis studies can also be performed at IPM Moscow [41]. Characteristics are available for the IPG-4 Plasmatron, located at IPM.…”

Simulation of Subsonic and Supersonic Flows in Inductive Plasmatrons

“…1 The efficient capabilities of the 100-kW IPG-4 plasmatron for the simulation of physicochemical processes accompanying the hypersonic entry of a vehicle aeroshell in the Martian atmosphere have been recently demonstrated. 3,4 But in fact, the potential capabilities of research and design facilities to simulate reacting flow physics and plasma/surface interaction can be revealed, if the measurements are properly combined with computational-fluid-dynamics (CFD) modeling. CFD modeling is an indispensable tool for aerothermal testing in order to carry out CFD codes validation, to rebuild flowfield in plasmatron, and to extract TPM catalycity, related to atom recombination, from heattransfer measurements.…”

“…11, the code used has been validated by a comparison against the computational results obtained in the von Kármán Institute (VKI) for Fluid Mechanics (Brussels) 5,8,12 and the IPM RAS. 4 Simulation of both underexpanded and overexpanded supersonic jets in the plasmatron has been carried out. A quite reasonable correspondence with the experimental data is observed.…”

“…Up to now there are few computations of the nonequilibrium air 5 and argon 6 plasma flows coupled with the rf electromagnetic field. In prior papers 4,7 the entire flowfield into plasmatron has been calculated separately in two, 7 three, 4 or several 8 computational zones. Usually, plasma torch is the first zone, jet flow around the model is the second one, and boundary layer on the test model is the third one.…”