E. A. Nagnibeda

Transport properties of a reacting gas mixture with strong vibrational and chemical nonequilibrium

Abstract Transport properties of multi-component reacting gas mixtures are studied on the basis of the kinetic theory in the case of strong vibrational and chemical nonequilibrium. Considered are the conditions when quasi-stationary distributions of the molecules over vibrational levels do not exist and level kinetic approach is developed. The formulas for the viscosity, diffusion and thermal conductivity coefficients in terms of the nonequilibrium level populations, gas temperature and elastic collision integrals are derived. The practical algorithm for the calculation of these coefficients is given and applied for the investigation of the heat transfer behind a plane shock wave.

TRANSPORT PROPERTIES IN REACTING MIXTURE OF POLYATOMIC GASES

The mathematical modeling of transport properties in reacting gases on the basis of kinetic equations for the distribution functions is given in this paper. Thermal and chemical nonequilibrium conditions are considered. The influence of rotational and vibrational excitation and chemical reactions on the pressure tensor, heat flux and diffusion velocity is investigated. The generalization of the Chapman-Enskog method is used at the different levels of the strong nonequilibrium mixture description. Three nonequilibrium models are presented: the level approach, the generalized multi-temperature approach and the one-temperature approach. The macroscopic equations for macroparameters are derived from the kinetic theory treatment, and the expressions for the pressure tensor, diffusion velocity and heat flux as well as for the transport coefficients are given. The role of the different rates of the various energy exchanges, the anharmonism of molecular vibrations and chemical reactions in the transport properties of reacting mixtures is discussed.

On the non-equilibrium kinetics and heat transfer in nozzle flows

Abstract In this paper the influence of different vibrational distributions on heat transfer and diffusion in expanding nozzle flows is studied. Non-equilibrium flows of N 2 /N and O 2 /O mixtures with dissociation, recombination and excitation of vibrational levels are considered. Vibrational distributions, gas dynamic parameters as well as the transport coefficients and total energy flux are computed along the nozzle axis using four approaches of the transport kinetic theory: a rigorous state-to-state approximation, quasi-stationary two-temperature models for harmonic and anharmonic oscillators and a thermal equilibrium one-temperature model. A comparison of vibrational distributions and transport properties obtained in different approaches is presented.

State-to-state nonequilibrium reaction rates

Abstract The paper studies the strongly nonequilibrium vibrational and chemical kinetics in a reacting gas flow in the state-to-state approach. Considered are exchange reactions, dissociation and recombination. The algorithms for calculation of reaction rate coefficients, depending on vibrational levels of components are developed on the basis of the kinetic theory. Formulas for reaction rate coefficients are obtained taking into account non-maxwellian velocity distributions.

Rate coefficients for the reaction N2(i)+N=3N: a comparison of trajectory calculations and the Treanor–Marrone model

Abstract The Letter deals with modelling of the rate coefficients for the dissociation reaction N2(i)+N=3N. The dependence of dissociation rate coefficients on the vibrational quantum level has been obtained by using trajectory calculations and the phenomenological Treanor–Marrone model. A comparison of the results obtained on the basis of different models is discussed and practical recommendations concerning the parameters of the phenomenological model are given.

STRONG NONEQUILIBRIUM EFFECTS ON SPECIFIC HEATS AND THERMAL CONDUCTIVITY OF DIATOMIC GAS

Abstract The specific heats and thermal conductivity in a diatomic gas with a strong vibrational nonequilibrium are studied starting from the kinetic equations for the distribution functions. Three models for the heat conductivity coefficients are considered. The first one is based on a rigorous kinetic theory treatment. In the second model the inelastic collision integrals are neglected and the thermal conductivity coefficients are expressed only in terms of standard elastic collision integrals and nonequilibrium specific heats. The third model uses the Eucken empirical formula with real gas specific heats. The results are compared with experimental data and with the results of other authors. The limits of the validity of the Eucken formula are estimated and a refinement for strong nonequilibrium is given. A simplified formula for the heat conductivity coefficient is proposed which closely agrees with the experimental data and with the exact kinetic model.

Multitemperature kinetic model for heat transfer in reacting gas mixture flows

Heat transfer in a high temperature reacting gas flow is investigated taking into account the influence of strong vibrational and chemical nonequilibrium. Rapid and slow vibrational energy exchanges in a mixture of molecular gases with realistic molecular spectra are taken into account and the deviation from the Boltzmann distribution over vibrational levels is studied. A kinetic theory approach is developed for the modeling of transport properties of a reacting mixture of polyatomic gases and a generalized multitemperature model is given. This theoretical model is applied for the analysis of the heat transfer and diffusion behind a strong shock wave propagating in air. The heat conductivity, diffusion coefficients, and heat flux are calculated on the basis of this model and compared to the one-temperature approach. The influence of anharmonicity of molecular vibrations is evaluated.

Nonequilibrium Kinetics and Heat Transfer in O2/O Mixtures near Catalytic Surfaces

Nonequilibrium vibrational-chemical kinetics and heat transfer in an O 2/O mixture near the surface of a space vehicle under reentry conditions are studied. Vibration-translation, vibration-vibration energy exchange, dissociation-recombination processes in the gas phase as well as heterogeneous recombination, dissociation, and deactivation of vibrational states on a silica surface are taken into account. The effect of nonequilibrium kinetics and surface catalysis on the total heat e ux and averaged dissociation-rate coefe cients is examined. It is shown that both heterogeneous recombination and dissociation on the surface must be incorporated in the kinetic scheme. The contribution of thermal conductivity, thermal and mass diffusion, and vibrational energy diffusion to theheat transfer is evaluated. In particular, vibrational energy diffusion near the surface is found to play an important role.

Influence of Nonequilibrium Kinetics on Heat Transfer and Diffusion near Re-Entering Body

The heat transfer and diffusion near the surface of a space vehicle under re-entry conditions are studied on the basis of the kinetic theory of gases. The influence of the nonequilibrium kinetics in an (N 2 , N) mixture on the transport properties of the flow is investigated. The nonequilibrium vibrational distributions in the boundary layer near the surface of the re-entering body have been obtained in the state-to-state approach and Inserted in the transport kinetic theory code. As a result, the total heat flux, thermal conductivity, and all diffusion coefficients are calculated under different conditions in the freestream and on the surface. The effects of various energy exchanges, vibrational nonequilibrium, dissociation, and recombination on the heat transfer and diffusion are examined

State-to-state theory of vibrational kinetics and dissociation in three-atomic gases

The paper deals with the kinetic theory of gas mixtures containing polyatomic molecules with several vibrational modes. The excitation of the rotational and vibrational degrees of freedom and dissociation are taken into account. The main attention is focused on the modeling of multi-level vibrational kinetics and vibration-dissociation coupling of linear three-atomic molecules. The model is applied for the study of shock heated gas flows and some new features of non-equilibrium kinetics of CO2 behind shock waves are found.