A hot gas facility for high-temperature spectrometry

A hot gas facility is described for determining molecular absorption data and validating spectroscopically based gas analyser systems. The facility comprises a newly developed heated 0.50 m stainless steel gas flow cell mounted with CaF2 windows, which can be operated from ambient to 1100 K. The heated cell is interfaced to a Fourier transform infrared spectrometer and a black body source, and is characterized by a uniform temperature profile over the entire path length.

This profile is demonstrated by measuring the gas temperature of carbon dioxide using spectroscopic methods based on transmission-emission spectra measured simultaneously and comparing the results of these measurements with those using thermocouples. It is found that the temperatures determined by spectroscopic methods are within the uncertainty of those measured by thermocouples (±2.9 K at 1072.0 K and ±0.7 K at 462.9 K).

The gas enclosed in the cell is therefore to be considered as a uniform slab of gas. In addition, the shape of the measured emission spectra, which are very sensitive to self-absorption effects caused by small amounts of cold gas molecules present in the light path, are shown to be equal to those of the transmittance spectra to within 1% (~1-2 K).

This indicates that the presence of cold gas molecules close to the windows and in the light path is negligible.