High-pressure,high-temperature thermophysical measurements on tungsten

Abstract

Wire shaped tungsten samples (0.25 mm diameter, 40 mm length, 99.97%) are resistively pulse heated as part of a coaxially built up capacitor discharge circuit. With heating rates of more than 10⁹ K/s, temperatures up to 12000 K are reached. The tungsten wire is contained with the surrounding medium water in a high pressure vessel with sapphire windows and a maximum pressure capability of 0.5 GPa. Time correlated measurements of the current through the wire and the voltage drop across it as well as surface radiation and wire expansion can be performed simultaneously and allow the determination of thermophysical properties for the liquid tungsten (see key words). All measuring systems have rise times less than 10 ns.     

Investigation of the hyperfine structure of Ta I lines (VI)

We have classified about 200 new lines and have discovered 13 energy levels with even parity and 1 level with odd parity by means of the systematic hyperfine structure investigation of a large number of spectral lines of the neutral tantalum atom. For the new levels we deduced their angular momenta, parity and magnetic hyperfine interaction constants A as well as the electric quadrupole interaction constants B. Received 8 August 2001     

Effect of flame thickness variation on the mass burning rate of premixed counterflow flames with an oscillating strain rate

The mass-based stretch rate is used to study the response of premixed axisymmetric counterflow flames subject to an oscillating strain rate. Integral analysis is used to estimate the mass burning rate of the oscillating counterflow flames. From this study it can be concluded that the flame responds in a nonlinear manner. With an increase of the applied strain frequencies, it is found that unsteady stretch effects arising due to flame thickness variations become significant and the mass-based stretch rate is able to capture these nonlinear effects. The inclusion of these unsteady stretch effects in the mass-based stretch helps the integral analysis to predict the mass-burning rate of oscillating flames more accurately.     

Experimental investigation of the hyperfine spectra of Pr I – lines: discovery of new fine structure levels with low angular momentum

We present 39 odd and 15 even parity newly discovered fine structure levels of Pr I with low angular momentum: J = 1/2, 3/2 and 5/2. Spectral lines in the range 4200 Å to 7500 Å were experimentally investigated using laser induced fluorescence spectroscopy in a hollow cathode discharge lamp. The levels were discovered by analysis of the recorded hyperfine patterns of the investigated transitions. With the help of these levels, 119 spectral lines were classified directly by laser excitation and 127 lines were classified as fluorescence lines.     

Progress in the analysis of the even parity configurations of tantalum atom

The experimental work of L. Windholz, G.H. Guthöhrlein and co-workers, concerning observation of the tantalum spectrum, yield many information about new energy levels and hyperfine structure splitting. We contribute the results of the complex parametric studies of the fine- and hyperfine structure of the mentioned element up to second-order of perturbation theory, including the effects of closed shell - open shell excitations. The work has been performed for the systems including 47 even configurations. The values of the radial parameters describing the one- and many-body interactions effects on atomic structure are given. We predicted values of energy levels and their A- and B- hyperfine structure constants, also for experimentally levels not observed up to now.     

Investigation of the hyperfine structure of TaI-line (II)

The hyperfine structure of several spectral lines of the neutral tantalum atom was investigated by means of saturated laser spectroscopy, detecting optogalvanic signals and/or laser induced fluorescence. From the spectra we could determine the magnetic hyperfine interaction constants A and the electric quadrupol interaction constants B of 11 levels of even parity and 13 levels of odd parity.     

Laserspectroscopic investigations of the lithium-D-lines in magnetic fields

Laser-atomic-beam investigations of the lithiumD ₁- andD ₂-line in magnetic fields were performed using cw-laser excitation and fluorescence detection. For both isotopes⁶Li and⁷Li, the hyperfine splittings of the ground level 2² S _1/2 and the upper level of theD ₁-line, 2² P _1/2, as well as the isotopic shifts of theD ₁- and theD ₂-line were determined from the registrations without field. In magnetic fields, Zeeman- and Paschen-Back-effects of the lines were studied. Using the Zeeman pattern of theD ₁-line for a calibration of the field strength, values for the hyperfine constantsA andB of the 2² P _3/2-level of⁷Li could be derived from the Zeeman pattern of theD ₂-line.     

Interaction of laser radiation with doppler-broadened media in coherent population trapping regime: law of light propagation

The influence of thermal motion of atoms on laser light propagation through a coherent optically dense medium is investigated theoretically. If the laser light intensity does not exceed a certain threshold value (intensity of coherent population trapping switching on multiplied by square of ratio of Doppler broadening to natural linewidth), the propagation law is strongly influenced by atomic motion: the laser intensity decreases neither exponentially, nor linearily, but as second-order polynomial of the optical depth. Above this threshold the propagation law is linear.     

The sodium D2-line in electric and magnetic fields

The splitting of the hyperfine structure of the D₂ line of the sodium atom was investigated under the influence of simultaneously acting parallel magnetic and electric fields of comparable strength. The experimental spectra were taken by laser-atomic-beam spectroscopy. Theoretical spectra obtained by quantum mechanical calculations agree very well with the experimentally observed spectra, therefore allowing their clear interpretation, especially at anticrossing regions.     

Effect of Soret diffusion on lean hydrogen/air flames at normal and elevated pressure and temperature

The influence of Soret diffusion on lean premixed flames propagating in hydrogen/air mixtures is numerically investigated with a detailed chemical and transport models at normal and elevated pressure and temperature. The Soret diffusion influence on the one-dimensional (1D) flame mass burning rate and two-dimensional (2D) flame propagating characteristics is analysed, revealing a strong dependency on flame stretch rate, pressure and temperature. For 1D flames, at normal pressure and temperature, with an increase of Karlovitz number from 0 to 0.4, the mass burning rate is first reduced and then enhanced by Soret diffusion of H₂ while it is reduced by Soret diffusion of H. The influence of Soret diffusion of H₂ is enhanced by pressure and reduced by temperature. On the contrary, the influence of Soret diffusion of H is reduced by pressure and enhanced by temperature. For 2D flames, at normal pressure and temperature, during the early phase of flame evolution, flames with Soret diffusion display more curved flame cells. Pressure enhances this effect, while temperature reduces it. The influence of Soret diffusion of H₂ on the global consumption speed is enhanced at elevated pressure. The influence of Soret diffusion of H on the global consumption speed is enhanced at elevated temperature. The flame evolution is more affected by Soret diffusion in the early phase of propagation than in the long run due to the local enrichment of H₂ caused by flame curvature effects. The present study provides new insights into the Soret diffusion effect on the characteristics of lean hydrogen/air flames at conditions that are relevant to practical applications, e.g. gas engines and turbines.