CO2-BASED THERMOMETRY OF SUPERCRITICAL WATER OXIDATION

We have demonstrated the suitability of CO2 Raman spectra as a thermometric probe of the fluid mixtures encountered in supercritical water oxidation. Measured temperature accuracies of +/- 6% are presented. Measurements were made of the upsilon-1, 2-upsilon-2 Fermi resonance features of CO2 in a supercritical water environment. Over the temperature range of interest to researchers of supercritical water oxidation, approximately 400-650-degrees-C, hot bands appear in the Raman spectrum of CO2 with sufficient spectral intensity to serve as a convenient measure of the fluid temperature. We have analyzed these hot bands by taking the ratio of their integrated intensity with the integrated intensity of the fundamental. Over the temperature range of 390 to 540-degrees-C, the intensity ratio of the first pure hot band feature to the fundamental of upsilon-1 shows a very nearly linear dependence on temperature. The experimental ratio measurements are well explained by standard Raman theory if the Fermi resonance is accounted for. As discussed, the CO2 spectral line shape is affected by the high pressure (P > 22.1 MPa) used in supercritical work, but these changes do not affect the extraction of a fluid temperature from the spectra.