Mark P. Freeman

Determination of the Radial Distribution of Brightness in a Cylindrical Luminous Medium with Self-Absorption

The two-path method (utilizing a mirror) is shown to provide sufficient information to solve for the true radial brightness distribution of a luminous medium in the presence of self-absorption. In the case where self-absorption is not large, an approximate solution to the problem is shown to be no more difficult than a solution for the “optically thin” approximation.

Determination of a Radiance-Coefficient Profile from the Observed Asymmetric Radiance Distribution of an Optically Thin Radiating Medium

A hypothetical experiment involving cross spectrographs is described in which the determination of the radiance-coefficient distribution of a circular optically thin asymmetric radiating medium is treated with some rigor. It is then shown that one may start from normal data (i.e., a single mildly asymmetric radiance distribution) and with equal rigor determine a radiance coefficient profile through the flame. Furthermore, it is shown that the solution is surprisingly indifferent to choice of center for reasonable errors of judgment. For purposes of intercomparison a numerical measure of asymmetry is proposed and some mention is made of the numerical techniques employed by the authors which seem to be exceptionally stable.

Velocity of Propagation and Nature of Luminosity Fluctuations in a Plasma Jet

The velocity of propagation of the luminous detail in a plasma jet was determined by the time required for transit between photomultiplier stations at different axial positions of an expanded plasma jet. The measurements were synchronized with power supply ripple to eliminate this as a random perturbation.It is found that the luminous fluctuations travel at two velocities. The slower fluctuations move with nearly the calculated speed of the jet and may therefore be ascribed to temperature or possibly composition fluctuations while the (much) faster fluctuations travel with jet speed plus local sonic velocity and are evidently pressure waves.

A QUANTITATIVE EXAMINATION OF THE LTE CONDITION IN THE EFFLUENT OF AN ATMOSPHERIC PRESSURE ARGON PLASMA JET

Abstract A sensitive and relatively unambiguous experimental test for local thermodynamic equilibrium (LTE) has been carried out 3 mm from the orifice of an unconfined atmospheric-pressure argon plasma jet with a front electrode L/D ratio of about 3. It was assumed only that the plasma consisted of the four species, argon atoms, metastable argon atoms, electrons, and argon ions, in intimate mixture. The Kramers-Unsold relation normalized by in situ use of an Olsen arc (a device taken to be in thermodynamic equilibrium) was used to determined from the continuum radiance coefficient the pointwise electron and hence argon ion concentration. The concentration of 19·22 eV excited argon ions was determined by absolute intensity measurement of the 4806·90 A line. The ratio of the concentration of these excited emitters to the measured total ion population was used in the appropriate Boltzmann equation to obtain a unique and sensitively determined ion-excitation temperature parameter, Tα. To demonstrate LTE, it remains only to show that the absolute populations of argon ions and of metastables, calculated by the well-known principles of statistical mechanics for temperature Tα, are in agreement with those observed. Ion populations were determined as described above, and metastable populations inferred from those for the 1·78 eV excited metastable state which gives rise to the 6965·43 A line. Finally, the ion excitation temperature profile was extrapolated in a reasonable way to the edge of the jet, and the theoretical heat flow was computed for a proportional velocity profile. Satisfactory agreement with measured heat flux was obtained.

Physical enhancement of high-temperature heterogeneously catalyzed reaction rates in molecular-scale capillaries

Abstract It is shown that for gas/solid heterogeneous catalysis in cavities a substantial augmentation of reaction rate (∼ four orders of magnitude) and reaction selectivity (one to two orders of magnitude) occurs as the capillary size is reduced to a few molecular diameters (the case in molecular sieve catalysts). This effect readily emerges from an interconsistent treatment of collision theory and high-temperature physical adsorption theory and is independent of the nature of the reactive sites. It is seen to be a nearly obvious effect from contemplation of the limiting relationships. That is, physical adsorption has virtually no effect on reaction rates for large capillaries, but for small capillaries, only that gas physically adsorbed will be available to react. This accounts for the selectivity enhancement. Because of the smallness of the capillaries, the mean-free path for collision becomes very small and this accounts for the increased activity.