Abstract
We present noninvasive, spatially resolved measurements on low-pressure, subsonic, laminar gas flows using Raman spectroscopy. From the Raman signal, the density and temperature of the flow can be extracted directly, with reasonable integration times (∼10 min-1 h). The use of a high-power laser diode makes it a very attractive low-cost, efficient technique. Temperatures studied range from 290 to 790 K; the spatial resolution was 2.5 × 1 mm2 in the flow cross section, and 10–20 μm in the flow direction, within a flow profile of diam. ∼ 15 mm. The flow was generated by a conical double-nozzle system with CO2 as the sample and Ar as the sheath gas. Vibrational and rotational state population and relaxation properties in the gas flow have been studied, and nonequilibrium conditions were found. A computational fluid dynamics (CFD) calculation is compared with the data; it supports the physical model suggested within the experimental errors.
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