CO2-Based Thermometry of Supercritical Water Oxidation

Abstract

We have demonstrated the suitability of CO₂ Raman spectra as a thermometry probe of the fluid mixtures encountered in supercritical water oxidation. Measured temperature accuracies of ±6% are presented. Measurements were made of the v₁ 2 v₂ Fermi resonance features of CO₂ in a supercritical water environment. Over the temperature range of interest to researchers of supercritical water oxidation, ∼400–650°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°C, the intensity ratio of the first pure hot band feature to the fundamental of v₁ 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.