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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

A survey of the reaction rate constants for the thermal dissociation and recombination of nitrogen and oxygen

The objective of the present report is to survey the various values of forward and backward reaction rate constants used by investigators in the field of high-temperature (T greater than 2000 K) gas reactions involving nitrogen and oxygen only. The objective is to find those values that correlate well so that they can be used for the studies of hypersonic flow and supersonic combustion with reasonable confidence. Relatively good agreement among these various values is observed for temperatures lower than 10,000 K.

Marraffa, Lionel↗
NASA NTRS1963

Tabulated Values of Bond Dissociation Energies, Ionization Potentials, and Electron Affinities for Some Molecules Found in High-Temperature Chemical Reactions

Values of the bond dissociation energies, ionization potentials, and electron affinities that were taken from the literature are presented in tables for some monatomic, diatomic, and polyatomic molecules which are found in many high-temperature chemical reactions including combustion reactions. Much of the information came from literature published after 1950 which either reported experimental and theoretical energy values or gave a review of previous literature on the subject. In some cases values for the bond dissociation energies were calculated from recently published heats of formation.

IONIZATION POTENTIAL↗
NASA NTRS2017

On the Development of a New Nonequilibrium Chemistry Model for Mars Entry

This paper represents a summary of results to date of an on-going effort at NASA Ames Research Center to develop a physics-based non-equilibrium model for hypersonic entry into the Martian atmosphere. Our approach is to first compute potential energy surfaces based on accurate solutions of the electronic Schroedinger equation and then use quasiclassical trajectory calculations to obtain reaction cross sections and rate coefficients based on these potentials. We have presented new rate coefficients for N2 dissociation and CO dissociation and exchange reactions. These results illustrate shortcomings with some of the rate coefficients in Parks original T-Tv model for Mars entries and with some of the 30-45 year old shock tube data. We observe that the shock tube experiments of CO + O dissociation did not adequately account for the exchange reaction that leads to formation of C + O2. This reaction is actually the primary channel for CO removal in the shock layer at temperatures below 10,000 K, because the reaction enthalpy for exchange is considerably lower than the comparable value for dissociation.

quasiclassical trajectory calculation↗
NASA NTRS2023

Effect of the Electrostatic Field due to the Surface Monolayer Metal Atoms on the Dissociation of Homonuclear Diatomic Gases in Gas-Metal Surface Reactions

The present paper examines the role of an electrostatic field generated by the outermost monolayer of metal ions prior to gas adsorption in aiding the dissociation of homonuclear diatomic gas molecules. The interaction of five homonuclear diatomic gases, Cl 2 , F 2 , H 2 , N 2 and O 2 , with several pure metals are examined using Coulomb’s law to calculate the attractive and repulsive forces between the electrons or ions in the gas molecule and the free surface metallic electrons or ions assuming a Bohr model. These calculations demonstrate that the total energy of the electrostatic fields from the metals can exceed the molecular binding energies of Cl 2 , F 2 , and O 2 at some distance from the metallic surface thereby suggesting that these gases interact primarily with the metallic surface in their atomic states after molecular bond dissociation prior to reaction. In contrast, H 2 and N 2 gases do not dissociate prior to reaching the metal surface due to the fact that the effective charge of the gas ions is less than the total electron charge at the outermost electronic shell. The present results correlate linearly with the electrochemical series standard reduction potential as well as with the Pauling electronegativity for several metals.

Gas-metal reactions↗
NASA NTRS1990

Assessment of chemical nonequilibrium in rarefied hypersonic flow

Calculations are presented of chemical nonequilibrium in the rarefied hypersonic flowfields surrounding reentering spacecraft in the upper atmosphere. The direct simulation Monte Carlo method is the solution technique employed. Methods by which chemical reactions are included in this simulation scheme are focused upon. In particular, the coupling of vibrational and dissociative nonequilibrium is investigated. The assumption of a fully excited mode has very little effect on the calculated results when the vibrational mode does not contribute to the energy available for reaction. A steric factor for dissociative reactions is developed which includes the vibrational energy of the dissociating molecule. Calculations are presented for the flow along the stagnation streamline of a blunt body for conditions representative of the entry and exit phases of the Aeroassisted Flight Experiment vehicle at an altitude of 90 km. It is found that both the flow properties and surface quantities are significantly affected by the introduction of the steric factor.

Boyd, Iain D.↗
NASA NTRS1983

Rate processes in gas phase

Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

Hansen, C. F.↗
NASA NTRS2000

A Model For The Burning of Teflon

Teflon has been identified as suitable material for use in oxygen-enriched atmospheres because of its low specific enthalpy of combustion that is, less than 1500 cal/gram. However, once ignited, Teflon burns in a heterogeneous reaction until total consumption or depletion of oxygen occurs. A model is developed for the burning of Teflon in pure, high-pressure oxygen, 3.4 to 68.9 MPa. The Teflon polymer chain dissociates via monomer units due to pyrolysis. These monomer units diffuse to the surface due to free convection. The model consists of coupled mass and energy balances for the polymer and an energy balance for the free convection of product gases. The model is used to obtain appropriate kinetic parameters for the dissociation and surface reactions. The model is validated against experimental measurements of Teflon discs supported on aluminum rods (2216) at oxygen pressures of 3.4, 6.8, 34.4, and 68.9 MPa. The model simulates the temperature distribution in the product gases above burning Teflon.

Waller, Jess M.↗
NASA NTRS1988

Comparison of vibration dissociation coupling and radiative heat transfer models for AOTV/AFE flowfields

A series of detailed studies comparing various vibration dissociation coupling models, reaction systems and rates, and radiative heating models has been conducted for the nonequilibrium stagnation region of an AFE/AOTV vehicle. Atomic and molecular nonequilibrium radiation correction factors have been developed and applied to various absorption coefficient step models, and a modified vibration dissociation coupling model has been shown to yield good vibration/electronic temperature and concentration profiles. While results indicate sensitivity to the choice of vibration dissociation coupling model and to the nitrogen electron impact ionization rate, by proper combinations accurate flowfield and radiative heating results can be obtained. These results indicate that nonequilibrium effects significantly affect the flowfield and the radiative heat transfer. However, additional work is needed in ionization chemistry and absorption coefficient modeling.

Carlson, Leland A.↗
NASA NTRS2006

Analysis of Material Sample Heated by Impinging Hot Hydrogen Jet in a Non-Nuclear Tester

A computational conjugate heat transfer methodology was developed and anchored with data obtained from a hot-hydrogen jet heated, non-nuclear materials tester, as a first step towards developing an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective and thermal radiative, and conjugate heat transfers. Predicted hot hydrogen jet and material surface temperatures were compared with those of measurement. Predicted solid temperatures were compared with those obtained with a standard heat transfer code. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

Wang, Ten-See↗
NASA NTRS1986

The reactive thermal conductivity of air at high temperatures

This paper presents the thermal conductivity of air from the dissociation and ionization reactions of the nitrogen and oxygen species in air from 1000 K to 25,000 K. The results for nitrogen are compared with results for the nonreactive (frozen) contribution to the thermal conductivity of the 'nitrogen system' (N2, N, N/+/, and the electron, e). At 6000 K, the contribution to the thermal conductivity from the dissociation of N2 is more than an order of magnitude greater than the frozen thermal conductivity and, at 15,000 K, the contribution to the thermal conductivity from the ionization of nitrogen atoms is about as large as the contribution from the frozen thermal conductivity.

Biolsi, L.↗
NASA NTRS1988

Numerical simulation of hypersonic inlet flows with equilibrium or finite rate chemistry

An efficient numerical program incorporated with comprehensive high temperature gas property models has been developed to simulate hypersonic inlet flows. The computer program employs an implicit lower-upper time marching scheme to solve the two-dimensional Navier-Stokes equations with variable thermodynamic and transport properties. Both finite-rate and local-equilibrium approaches are adopted in the chemical reaction model for dissociation and ionization of the inlet air. In the finite rate approach, eleven species equations coupled with fluid dynamic equations are solved simultaneously. In the local-equilibrium approach, instead of solving species equations, an efficient chemical equilibrium package has been developed and incorporated into the flow code to obtain chemical compositions directly. Gas properties for the reaction products species are calculated by methods of statistical mechanics and fit to a polynomial form for C(p). In the present study, since the chemical reaction time is comparable to the flow residence time, the local-equilibrium model underpredicts the temperature in the shock layer. Significant differences of predicted chemical compositions in shock layer between finite rate and local-equilibrium approaches have been observed.

Yu, Sheng-Tao↗
NASA NTRS2006

Multiphysics Thermal-Fluid Design Analysis of a Non-Nuclear Tester for Hot-Hydrogen Materials and Component Development

The objective of this effort is to perform design analyses for a non-nuclear hot-hydrogen materials tester, as a first step towards developing efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber design and analysis. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective, and thermal radiative heat transfers. The goals of the design analyses are to maintain maximum hot-hydrogen jet impingement energy and to minimize chamber wall heating. The results of analyses on three test fixture configurations and the rationale for final selection are presented. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

Wang, Ten-See↗
NASA NTRS1972

Molecular dynamics - The dissociation of H2 by He.

The dissociation of molecular hydrogen by helium was studied at 5500 deg K using the quasiclassical approximation. The temperature-dependent reaction cross sections were very dependent on the initial quantum states of the molecule. A rate constant was estimated for the dissociation reaction, and agreement between theory and experiment was satisfactory.

Brown, N. J.↗
NASA NTRS1978

Organic chemistry on Titan

Observations of nonequilibrium phenomena on the Saturn satellite Titan indicate the occurrence of organic chemical evolution. Greenhouse and thermal inversion models of Titan's atmosphere provide environmental constraints within which various pathways for organic chemical synthesis are assessed. Experimental results and theoretical modeling studies suggest that the organic chemistry of the satellite may be dominated by two atmospheric processes: energetic-particle bombardment and photochemistry. Reactions initiated in various levels of the atmosphere by cosmic ray, Saturn wind, and solar wind particle bombardment of a CH4 - N2 atmospheric mixture can account for the C2-hydrocarbons, the UV-visible-absorbing stratospheric haze, and the reddish color of the satellite. Photochemical reactions of CH4 can also account for the presence of C2-hydrocarbons. In the lower Titan atmosphere, photochemical processes will be important if surface temperatures are sufficiently high for gaseous NH3 to exist. Hot H-atom reactions initiated by photo-dissociation of NH3 can couple the chemical reactions of NH3 and CH4 and produce organic matter.

Chang, S.↗
NASA NTRS1995

Rotational And Rovibrational Energy Transfer In Electron Collisions With Molecules

Air flows around a hypervelocity reentry vehicle undergo dissociation, rovibrational excitation and ionization. More specifically the air, initially 80% N2 and 20% O2, in the shock layer consists of species such as N, O, N2, O2, NO, N+, O+, N+, O+, NO+ and 2 free electrons. It was pointed out in multi temperature models'' that the temperature of the rotational energy modes and the gas-kinetic translational temperature are quickly equilibrated by a few collisions and rise rapidly to high temperatures as 50000K before falling off to equilibrium value of 10000K. Contrary, the electronic and vibrational temperatures state energy distributions remain low (less than 15000K) because of the slow equilibration. Electron vibrational energy transfer is thought to play a crucial role in such a ionizing flow regime since chemical reaction rates and dissociation depend strongly on the vibrational temperatures. Modeling of these flowfields in principle require the rovibrational excitation and de-excitation cross section data for average electron energies from threshold up to several eV (leV=11605.4 K). In this lecture we focus on theoretical description of rotational effects i.e. energy transfer of electrons to molecules such that the molecular rotational (vojo goes to voj) or vibrational and rotational (v(sub 0)j(sub 0) goes to vj) states are changed. Excitation and de-excitation of electronic states was discussed in a previous talk at this conference.

Thuemmel, Helmar T.↗
NASA NTRS1990

Theoretical studies of important processes in planetary and comet atmospheres

Dissociative recombination (DR) reactions in planetary and comet atmospheres are discussed. A computer program was developed which determines DR cross sections and rates using potential curves and electronic capture widths. It uses Multi-Channel Quantum Defect Theory (MQDT) to include excited Rydberg resonance levels in the DR cross section and rate calculations. Each vibrational level of a molecular ion is the limit for an infinite series of Rydberg states. Above each ion vibrational level are Rydberg vibrational levels having higher ion levels as their series limit. These Rydberg vibrational levels are resonances, i.e., neutral states which are imbedded in the electron-molecular ion continuum. The process in which the Rydberg level causes an abrupt perturbation in the cross section for DR (because of interference between capture into the Rydberg level and capture into the repulsive dissociative state) is referred to as indirect recombination. The process in which the Rydberg levels are excluded and recombination goes from the entrance channel to the repulsive state is called direct recombination. The full DR process, i.e., both direct and indirect recombination, is the process of importance for planetary atmospheres. These ideas are illustrated with the new results for DR from excited ion vibrational levels of O2(+) into the dissociative state which leads to O(1S) + O(1D).

Guberman, Steven L.↗