Cavity ring down absorption of oxygen in air as a temperature sensor Carlos E. Manzanares and Parashu R. Nyaupane Department of Chemistry and Biochemistry Baylor University, Waco, TX 76798

Optical Cavity Our current research uses the phase shift method for determining the photon lifetime within the optical cavity

PS-CRD The absorption spectrum is obtained by : The PS method obtains the lifetime from the change in phase angle after passing through a CRD cavity using: The absorption spectrum is obtained by :

Low Temperature Cryostat Liquid N2 Path length range : (2- 6)Km Lewis, E.K., Moehnke, C.J., Manzanares, C. Rev. Sci. Instrum. 2006, 77,073107

For our low resolution spectra the only transitions considered are the PP transitions that correspond to absorptions from the ground state rotational quantum number J”= K” = 1, 3, 5, 7…, with final states J’ = 0, 2, 4, 6…, respectively.

Open cavity

# Peaks Aver. Slope/10-3 cm Intercept Calculated Temp (K) Measured Temp (K) 6 ‒ (16.4 ± 0.8) ‒ (24.32 ± 0.09) 88 ± 5 90 4 ‒ (9.62 ± 0.54) ‒ (24.60 ± 0.12) 150 ± 8 150 7 ‒ (4.78 ± 0.09) ‒ (25.47 ± 0.02) 301 ± 6 298 ‒ (4.40 ± 0.10) ‒ (25.58 ± 0.03) 327 ± 8 321 2 ‒ (4.13 ± 0.12) ‒ (25.62 ± 0.03) 348 ± 11 356 1 ‒ (3.76 ± 0.15) ‒ (25.67 ± 0.04) 386 ± 15 383

Summary The study has shown that the oxygen absorption is a very good choice to determine temperature in a flow system. Although it will be ideal to have a diode laser to resolve the peaks, the study has shown that a low resolution spectrum is capable of giving the correct temperature of the flowing air. The flowing air temperature sensor will be used to measure the temperatures of cooling air at the input (cold air) and output (hot air) after cooling the blades of a laboratory gas turbine. The results could contribute to improvements in turbine blade cooling design.

Robert A. Welch Foundation Acknowledgement Robert A. Welch Foundation Baylor University Undergraduate Research and Scholarly Achievement (URSA) Program