Lifetime Surface Phosphor Thermometry - Technique Developments, Sources of Error, and Applications
Sammanfattning: Temperature is not only a fundamental aspect of everyday life, but it is also an essential metric for thermal conversion systems concerning efficiency, emissions, and component lifetime estimation. Therefore, a vast range of different methods to measure temperature has been developed. The technique of focus in this thesis is lifetime-based surface phosphor thermometry.In phosphor thermometry, one leverages the changes in luminescence of materials called phosphors to measure temperature. The spectral changes can result from shifts in the relative intensity of emission lines in the spectra or shifts in emission line wavelength with temperature. In addition, changes in the lifetime of the phosphorescence signal with temperature can be utilized for thermometry. Inorganic phosphors are ceramic substances that can operate with a range of luminescence activators. Most often, the luminescence originates from trivalent lanthanide ions or transition metal ions doped in a host crystal.Surface phosphor thermometry has the benefit of being a remote sensing technique, where one coats a phosphor on a surface of interest. This phosphor coating is then excited with a remote source, for example, pulsed laser light, and the phosphor luminescence is detected remotely. In this thesis, technology developments, error sources analysis, and applications of phosphor thermometry are presented. The technology developments present a high-temperature calibration system and a method for analyzing the lifetime components in the luminescence decay of phosphors in detail. An analysis of upconversion phosphors for temperature measurements beneath thermal barrier coatings and an investigation of high-temperature phosphors to 1900 K and their sensitivities to the oxygen content of the gas environment are also included in this work.The investigations into potential error sources include how PMT nonlinearity effects can influence the measured lifetime with excitation frequency from 10 Hz up to 10 kHz. In addition, the phosphor luminescence decay time impact of high repetition excitation was also investigated and analyzed to see potential error sources for temperature measurements.Phosphor thermometry was also used in two applications, including measuring the surface temperature of burning wood pellets and the surface temperature of a combustion nozzle in a down-scaled gas turbine combustor using hydrogen-enriched methane as fuel.
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