Raman Scattering in Two-Phase Flows with Application to Temperature Measurements
In several important applications of dispersed, two-phase flow, the possible occurrence of thermodynamic nonequilibrium between the vapor and liquid phases is of fundamental interest and practical concern. The measurement of the potential super-heated temperatures of the vapor, in the presence of colder liquid droplets remains a difficult experimental task, and to date, only partial success has been obtained by use of intrusive, aspirating thermocouple probes.
Laser Raman spectroscopy is a nonintrusive optical technique which has been developed as a diagnostic probe for gas dynamic studies. The feasibility of using Raman scattering to measure vapor temperatures in gas-liquid two-phase flows is under investigation here. A Raman system developed for the two phase measurements is described and experimentally obtained vibrational Raman bands are presented.
The Stokes vibrational Raman band was measured for single-phase steam at atmospheric pressure, with 20 to 190 K vapor superheat. Integrated intensity ratios, calculated from these spectra, are calibrated, and can be used for temperature measurements.
Water droplets, in gas-liquid two-phase samples, cause Mie and Raman scattering which interfere with the desired vapor measurement. Raman spectra, measured for atmospheric nitrogen in an air/water mist, show that Stokes vibrational spectra for the gaseous phase can be measured in dispersed two-phase samples. The principles and apparatus used for the above two-phase flow can be used for nonequilibrium two-phase flows for the measurement of vapor temperature.
KeywordsWater Droplet Raman Band Atmospheric Nitrogen Band Shape Laser Raman Spectroscopy
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