Rivera Guzmán, Leslie A.

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    Design and characterization of non-invasive thermal sensors for Laser Induced Fluorescence Thermometry (LIFT)
    (2005) Rivera Guzmán, Leslie A.; Rivera, Luis A.; College of Arts and Sciencies - Sciences; Mina, Nairmen; Robledo, Cynthia; Vega, Carmen; Department of Chemistry; Díaz, Ricardo
    Laser Induced Fluorescence Thermometry (LIFT) is a technique based on imaging to measure the temperature of a substance. The substance is doped with small concentrations of a natural fluorescent dye. LIFT takes advantage of the fluorescence properties of a substance in response to excitation from a laser source. It is selective to a specific wavelength range of emission, it reacts quickly and the temperature can be measured for highly dynamic systems. The objective of the present work is to apply LIFT to measure the thermal history of micron size in-flight droplets and for microscale nucleate boiling processes using water as the main working fluid. For these purposes two LIFT sensors have been developed. Pyrene, which is one of the most widely studied sensitive organic dyes, was one of the sensors evaluated. To perform the experiments in water it was necessary to add surfactants to enhance Pyrene’s solubility in water. A protocol, which considers several parameters, was designed and evaluated to prepare the solutions for the fluorescence studies. The second set of water based temperature sensors were Rhodamine B and the mixture Rhodamine B/Rhodamine 110. Rhodamine B and Rhodamine 110, are very soluble in water and therefore did not required additives. Even though the addition of surfactants was not required for solubilization, they were used to enhance their fluorescence intensities. Rhodamine 110 was used as a non-temperature sensitive reference dye. A mixture of dyes was used because, in principle, the variation in exciting light intensity due to refraction of the light passing through the thermal field was avoided. In general, the fluorescent dyes studied showed fluorescence emission intensities in the range of 1.0 x 10⁷ to 1.5 x 10⁷, which depend directly upon temperature. The requirements to develop a robust sensor for LIFT were fulfilled. The water-based sensors studied were selective to a specific wavelength range, sensitive to temperature from ambient to near boiling point range, reversible to temperature changes, and reproducible within the experimental error.