Engineering topics

Kunc, Joseph A.

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

10 records

NASA NTRS1991

Viscosity of high-temperature iodine

The viscosity coefficient of iodine in the temperature range 500 - 3000 K is calculated. Because of the low dissociation energy of the I2 molecules, the dissociation degree of the gas increases quickly with temperature, and I + I2 and I + I collisions must be taken into account in calculation of viscosity at temperatures greater than 1000 deg. Several possible channels for atom-atom interaction are considered, and the resulting collision integrals are averaged over all the important channels. It is also shown that the rigid-sphere model is inaccurate in predictions of the viscosity.

Kang, Steve H.↗

NASA NTRS1991

The V-T energy transfer in collisions of diatomics

A general approach evaluating the transition probabilities for the V-T exchange, involving highly excited levels and the Delta-v greater than 1 transitions, in diatomic gases is presented. Examples of numerical results are given for a number of transitions in nitrogen and oxygen molecules in the ground electronic states. The approach can be used for the V-T exchange involving diatomic molecular ions.

Kunc, Joseph A.↗

NASA NTRS1990

Central-force potentials for interaction of rotationally and vibrationally excited molecules

A general and computationally efficient approach evaluating the central-force potentials for interaction of rotationally and vibrationally excited molecules and molecular ions is presented. Examples of numerical calculations are given for interactions of diatomic systems (H2, N2 and O2) in ground electronic states. The approach can be applied in a straightforward way to interactions of atoms and atomic ions with diatomic molecules in arbitrary rotational-vibrational states.

Kunc, Joseph A.↗

NASA NTRS1990

Model gases for the detailed study of microscopic chemical nonequilibrium in diatomic gas flows

It is shown that chlorine (Cl2) and iodine (I2) are suitable model diatomic gases to use in theoretical studies of chemical nonequilibrium that account for rotational and vibrational as well as electronic processes in a gas. Because of the low temperature at which significant dissociation can be achieved in iodine, it is a particularly attractive candidate for the study of relatively low temperature chemically reacting flows, permitting detailed knowledge of the nonequilibrium populations of translational, rotational, vibrational and electronic energy levels. A preliminary investigation indicates that a useful iodine flow facility can be constructed and that diagnostic techniques are available to validate in detail prediction techniques for nonequilibrium flows.

Kunc, Joseph A.↗

NASA NTRS1989

Energy loss of fast nonthermal electrons in plasmas

Simple analytical expressions for equilibration times of nonrelativistic monoenergetic electrons in plasmas are evaluated in the 'weak'-beam approximation when the density of the monoenergetic electrons is much smaller than the plasma density. The equilibration time is defined as the time needed by the beam of monenergetic electrons to lose most of its energy as a result of collisions with plasma particles having a Maxwellian energy distribution. The process of energy equilibration is treated as a statistical superposition of both elastic and inelastic collisions in the plasma. The possibility of collisionless equilibration is discussed. Comparison of the equilibration times with the Spitzer relaxation times indicates that the former times are more appropriate for an estimate of the energy loss of the 'weak' electron beams in highly ionized plasmas.

Kunc, Joseph A.↗

NASA NTRS1989

Effect of rotational and vibrational excitation on interaction of diatomic molecules

A general and computationally efficient approach evaluating the central-force potentials for interaction of rotationally and vibrationally excited molecules and molecular ions is presented. Examples of numerical calculations are given for interactions of diatomic systems (H2, N2 and O2) in ground electronic states. The approach can be applied in straightforward way to interaction of atoms and atomic ions with diatomic molecules in arbitrary rotational-vibrational states.

Kunc, Joseph A.↗

NASA NTRS1989

Semiclassical approach to atomic and molecular interactions

A general approach, combining quantum and classical mechanics, is used to determine the electron position and velocity distributions in atoms and atomic ions (positive and negative). The Hartree-Fock electronic wave functions and the classical central field approximation are used for evaluation of the dynamic properties of the localized electrons. The distributions, which are of fundamental importance in applications of the binary encounter approximation to description of atomic and ionic collissions, are obtained in the form of simple analytical expressions. The quantum-classical distributions of this work are compared with several other distributions in Ne, Ar, and Al atoms in the ground state.

Kunc, Joseph A.↗

NASA NTRS1988

Quantum-classical electron distributions in atoms and atomic ions

A quantum-classical approach is used to obtain the velocity distributions in atoms and positive and negative ions in both ground and excited states. In the analysis, Hartree-Fock electronic wavefunctions are used to determine the radial electron distributions, and the central-field approximation is used to study the the dynamic properties of the localized electrons. The distributions for the outer and inner shells are found to agree well with exact results obtained by numerical calculations.

Kunc, Joseph A.↗

NASA NTRS1988

Transport of low- and medium-energy electron and ion beams in seawater and its vapors

A general theory of stopping power for electrons and ions in a target medium (gas, liquid, or thin solid foil) containing neutral as well as positive and negative ions is developed. The approach is quite accurate in the low- and medium-energy range (less than 1 MeV), where the Bethe stopping-power cross section is inaccurate. The energy transfer during individual collisions is treated by the binary-encounter approximation. The theory is applied to determine the stopping power of seawater, whose major components are H2O molecules and Na(+) and Cl(-) ions. The stopping-power cross sections for low- and medium-energy protons in water show excellent agreement with existing measurements.

Erwin, Daniel A.↗

NASA NTRS1988

Determination of electron density and temperature in non-LTE plasmas from spectral lines of impurity ions

A novel approach for calculating the populations of the excited Li-like ions C IV, N V, O VI, and Ne VIII is presented. The populations of the 2(2P), 3(2S), 3(2P), and 3(2D) electronic levels in these ions in optically thin plasmas with a broad range of electron density, N(e), and temperature, T(e), are determined from the collisional-radiative model by solving the system of rate equations for the production of excited ions; the equations are linear with respect to the excited ion populations, and the N(e) and T(e) are taken as independent variables. These populations are used to determine the ratios of line intensities for dipole allowed transitions between various energy levels. This approach can be applied to impurities other than the lithiumlike ions and is especially useful for diagnostics of systems where nonintrusive spectroscopic techniques must be used.

Kunc, Joseph A.↗