Engineering topics

Kunc, J. A.

Publications and source records attributed to Kunc, J. A..

At least 19 records

NASA NTRS1992

Relaxation of higher vibrational states in diatomic gases

A general and computationally efficient approach evaluating the transition probabilities for the V-T exchange, involving highly excited levels and the transitions of delta-v of more than 1, in diatomic gases is presented. The role of the repulsive part of the intermolecular potential on the transition probability is also investigated. Examples of numerical results are given for number of transitions in nitrogen and oxygen molecules in the ground electronic states. The approach can be used for interactions involving diatomic molecular ions.

Kunc, J. A.↗

NASA NTRS1992

Viscosity of dissociating gases

Recent calculations of the viscosity of iodine suggest that existing predictions of viscosities of high-temperature (up to several thousands degrees) gases should be revised, with much more attention being paid to the atomic and molecular interactions in the gas. As the gas starts to dissociate, the frequency of atom-molecule and atom-atom interactions increases, and those collisions must be taken into account in calculations of viscosity at high temperature. In this study, the iodine is chosen as an example, and the dependence of its viscosity on the gas dissociation degree is shown. Several possible channels for I+I interaction are considered in addition to I+I2 and I2+I2 collisions, and the resulting collision integrals are averaged over all the important channels.

Kang, S. H.↗

NASA NTRS1992

A code validation strategy and facility for nonequilibrium, reacting flows

The rotational and vibrational population distributions in a hypersonic flow of hot iodine vapor were investigated using a pilot wind tunnel. The tunnel provides run times of about 20 min, with a scale-up to a larger facility appearing to be possible. It will provide a 20-cm-diameter, Mach 9 flow of iodine vapor with only small amounts of free stream nonequilibrium. An analysis of the flow response to a normal shock wave indicates that significant chemistry will occur in model flow fields in the larger facility.

Muntz, E. P.↗

NASA NTRS1992

Dissociation energy of molecules in dense gases

A general approach is presented for calculating the reduction of the dissociation energy of diatomic molecules immersed in a dense (n = less than 10 exp 22/cu cm) gas of molecules and atoms. The dissociation energy of a molecule in a dense gas differs from that of the molecule in vacuum because the intermolecular forces change the intramolecular dynamics of the molecule, and, consequently, the energy of the molecular bond.

Kunc, J. A.↗

NASA NTRS1992

An iodine hypersonic wind tunnel for the study of nonequilibrium reacting flows

A pilot scale hypersonic wind tunnel operating on pure iodine vapor has been designed and tested. The wind tunnel operates intermittently with a run phase lasting approximately 20 minutes. Successful recirculation of the iodine used during the run phase has been achieved but can be improved. Relevant issues regarding the full scale facility's design and operation, and the use of iodine as a working gas are discussed. Continuous wave laser induced fluorescence was used to monitor number densities within the plume flowfield, while pulsed laser induced fluorescence was used in an initial attempt to measure vibrational energy state population distributions. Preliminary nozzle flow calculations based on finite rate chemistry are presented.

Pham-Van-diep, G. C.↗

NASA NTRS1991

Analytical ionization cross sections for atomic collisions

General analytical expressions for cross sections for direct ionization in atom-atom collisions are evaluated using the classical impulse approximation. The approach is also applied to ion-atom and molecule-molecule interactions. The overall accuracy of the obtained cross sections in a broad range of energy is better, when compared with existing measurements for many collision systems, than accuracy of other analytical predictions available in literature.

Kunc, J. A.↗

NASA NTRS1991

Cross sections and rate coefficients for inelastic interactions of heavy particles

The existing analytical inelastic cross-sections for direct atom-atom ionizing collisions of Firsov (1959), Fleischmann et al. (1972), and Drawin (1968) are discussed. General analytical expressions for direct ionization cross-sections in atom-atom collisions are derived. The main advantage of the present cross-sections is their generality, simplicity, and overall accuracy, which is acceptable in most applications and is better than the overall accuracy of the cross-sections of Firsov, Fleischmann et al., and Drawin. The atom-atom interaction is considered as a superposition of all the pairwise interactions between the test particle and all the electrons of the outer nl shell of the target atom. Such a picture of atom-atom collision is acceptable at low- and medium-impact energies because then the electrons of the outer shell of the target atom are most likely the ones that get ionized. At high-impact energy, the picture becomes inaccurate because of strong overlapping of the atomic shells.

Kunc, J. A.↗

NASA NTRS1991

Effect of the rotational-vibrational excitation on molecular diameters

The kinetic molecular diameters of rotationally and vibrationally excited diatomic molecules and molecular ions are derived as functions of the rotational and vibrational quantum numbers of the molecules. Typical molecular diameters are studied in two cases: in low-temperature gas, where the molecular diameter is independent of the degree of rotational-vibrational excitation of the molecules, and in high-temperature gas, where the molecular diameter depends on the degree of rotational-vibrational excitation of the molecules. The rotational-vibrational excitation of molecules is shown to have a meaningful effect on the collisional properties of gases. The effect is stronger in gases of weakly-bound molecules.

Kang, S. H.↗

NASA NTRS1991

Electron Boltzmann equation in nonthermal plasmas

Numerical and analytical solutions of the electron Boltzmann equation for a two-temperature steady-state He plasma are examined in a broad range of conditions, i.e., atom temperature ranging from 5000 K to 20,000 K; electron temperature ranging from 10,000 K to 20,000 K; and atom density ranging from 10 to the 10th to 10 to the 18th per cu cm. The WKB analytical solution is shown to be satisfactory in most situations. Attention is also given to the deviation of the electron distribution from Maxwellian, and to the possibility of raising the tail of the distribution.

Kunc, J. A.↗

NASA NTRS1991

Kinetics and continuum emission of negative atomic ions in partially ionized plasmas

Kinetics and continuum emission of negative ions are studied in stationary atomic hydrogen, nitrogen, and oxygen plasmas. The intensity of the negative-ion emission was found to be neglibible when compared to those of bound-bound and free-bound emission at low and medium particle densities. However, the negative-ion continuum emission can contribute significantly in certain parts of the emission spectrum at high particle densities.

Soon, W. H.↗

NASA NTRS1991

The negative ions emission in nitrogen

The contribution of negative atomic ions to continuum radiation in nitrogen plasma is discussed. It is shown that both unstable N(-)(3P) and metastable N(-)(1D) ions have a significant effect on the total production of the continuum radiation at electron temperatures below 12,000 K.

Soon, W. H.↗

NASA NTRS1990

Radiation of partially ionized atomic hydrogen

A nonlinear collisional-radiative model for determination of production of electrons, positive and negative ions, excited atoms, and spectral and continuum line intensities in stationary partially ionized atomic hydrogen is presented. Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions. It is found that the contribution of the negative ion emission to the total continuum emission can be important. Comparison of the calculated total continuum emission coefficient, including the negative ion emission, is in good agreement with experimental results.

Soon, W. H.↗

NASA NTRS1990

Negative radiation in partially ionized gas

A stationary, nonlinear collisional-radiative model for high-temperature atomic oxygen is presented. Populations of negative ions, electrons, positive ions and excited atoms and intensities of spectral, continuum and dielectronic recombination radiation are calculated in a wide range of conditions. Calculated total continuum emission is in good agreement with existing measurements. The contribution of the negative ion emission to the total continuum emission is found to be significant.

Soon, W. H.↗

NASA NTRS1990

Kinetics of metastable atoms and non-Maxwellian electrons in two-temperature plasmas

Numerical and analytical solutions of the electron Boltzmann equation in two-temperature steady-state helium plasma are studied in a broad range of conditions T(a) = 5,000-20,000 K, T(e) = 10,000-20,000 K; N(a) = 10 to the 10th - 10 to the 18th per cu cm. The WKB analytical solution is found to be satisfactory in most situations. The deviation of the electron distribution from Maxwellian and a possibility of raising of the tail of the distribution in presence of sources of fast electrons is also discussed.

Kunc, J. A.↗

NASA NTRS1990

Thermal nonequilibrium in partially ionized atomic oxygen

A stationary, nonlinear collisional-radiative model for high-temperature atomic oxygen is presented. Populations of electrons, ions, and excited atoms and intensities of spectral, continuum, and dielectronic recombination lines are calculated in a wide range of conditions. Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the concept of the escape factors that are not constant but dependent upon plasma conditions. The calculated total continuum emission is in good agreement with existing measurements.

Soon, W. H.↗

NASA NTRS1989

Collisional-radiative nonequilibrium in partially ionized atomic nitrogen

A nonlinear collisional-radiative model for determination of nonequilibrium production of electrons, excited atoms, and bound-bound, dielectronic and continuum line intensities in stationary partially ionized atomic nitrogen is presented. Populations of 14 atomic levels and line intensities are calculated in plasma with T(e) = 8000-15,000 K and N(t) = 10 to the 12th - 10 to the 18th/cu cm. Transport of radiation is included by coupling the rate equations of production of the electrons and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions.

Kunc, J. A.↗

NASA NTRS1989

Radiation of hot atomic hydrogen

A nonlinear collisional-radiative model for the determination of nonequilibrium production of electrons, ions, excited atoms, and spectral and continuum line intensities in stationary partially-ionized atomic hydrogen is presented. Transport of radiation is included by coupling the rate equations for production of the electrons and excited atoms with the radiation escape factors which are not constant but depend on plasma conditions.

Kunc, J. A.↗

NASA NTRS1989

Collisional-radiative non-equilibrium in high-temperature helium

A stationary, nonlinear collisional-radiative model for determination of production of electrons, excited atoms and atomic line intensities for high-temperature helium is presented. The populations of several atomic levels and the intensities of spectral and continuum lines are calculated in a wide range of conditions (Te = 12,000-22,000 K, Nt = 10 to the 12 - 10 to the 20th per cu cm. Transport of radiation is included by coupling the rate equations for production of the electrons and excited atoms with the radiation escape factors which are not constant but depend on plasma conditions.

Kunc, J. A.↗