Scientific Results

Infrared diode laser absorption features of N2O and CO2 in a laval nozzle

Year: 1992

Authors: Baldacchini G., Chakraborti P.K., D’Amato F.

Autors Affiliation: Dip. Sviluppo Tecnologie di Punta, ENEA, Area INN, P.O. Box 65, Frascati (Rome), I-00044, Italy

Abstract: Design and operation of a pulsed Laval nozzle and the characterization of molecular flow through such a nozzle using IR tunable diode laser (TDL) is the central theme of this work. The results here deal with He diluted N2O and CO2 gaseous systems. Boltzmann type plots of the spectral intensity data of both N2O and CO2 show non-linear behaviour. We have attempted to understand this non-linear behaviour of Boltzmann plots in terms of (1) instability in the jet and (2) a two-temperature model for the flowing gas, a cold central core and a hot boundary layer close to the nozzle walls. The model based on jet instability represents the data somewhat poorer than the two-temperature model. The parameters derived from fitting our experimental data to the former model could be used to calculate the thermodynamic parameters only through further approximations. Measured absorption line profile of the P(15) line of the v 2 band of N2O as a function of axial distance from the nozzle exit gradually shifts from a Lorentzian to a Gaussian type. Velocity distribution of N2O molecules in a Laval nozzle is determined by differentiating the absorption line profile of the P(15) line (v 0=576.235 cm–1) of the v 2 band of N2O. Translational temperature of N2O molecules is determined from the observed spectral profiles.


Volume: 55 (1)      Pages from: 92  to: 101

KeyWords: Molecular beam; Diode laser; N2O; CO2
DOI: 10.1007/BF00348620

Citations: 3
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