DOE OSTI · 1069310
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Allison, Stephen W., Gillies, George T.. 2011-11-01. Phosphor thermometry at the cellular level. https://doi.org/10.1109/fiiw.2011.6476833
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Since the last International Temperature Symposium, phosphor thermometry has continued to mature with considerable attention given to combustion and turbine engine applications. More recently the utility to problems on the micro- and nano-scales has appreciated, particularly in regard to biological and biomedical situations. The method is therefore used for a wide range of situations. Signal interpretation is important and experience teaches that without sufficient care phosphor signals can be misleading. In order to advance the method, signal analysis investigations should prove fruitful. The specific aspect addressed here is the question of waveform sampling. A simple phenomenological approach is described that explores how the number of points digitized per waveform affects the measurement repeatability and accuracy. This is demonstrated for single shot signals and the average of 512 sequential waveforms. A bright temperature-independent luminescence signal from YVO4:Eu is sampled every 800 ps for a highly sampled condition and every 8 microseconds for a low sampled condition. When the average of 512 waveforms are compared for the two sampling conditions, they differ by only 0.4%. For the highly sampled case, a noisy single shot waveform compared to the averaged waveform differed by 1.8%. Future efforts on this subject will address intermediate and lower sampling rates. Also, variable window techniques should be explored that are especially important for non-log-linear signals. Investigations, such as this, give the developer the requisite information for designing analysis systems appropriate for the intended application in terms of precision, accuracy, and response time.
Abstract: A transformative calibration methodology is presented for predicting transient surface temperatures in a thermally conducting medium from in-depth, time-varying temperature measurements. The surface temperature is resolved using two experimental runs and a newly devised first-kind Volterra integral equation. The first experimental run involves calibration with known surface temperature while the second run involves resolving the surface temperature of interest through the ill-posed integral equation. This paper presents the concept genesis and numerically demonstrates the concept for feasibility, robustness, stability and accuracy. From this demonstration, we propose to implement surface placed thermographic phosphors in the calibration stage of the inverse method for estimating the required surface temperature. As a preliminary study, we consider transient, constant property, onedimensional heat conduction in a semi-infinite medium. It is mathematically demonstrated that a Volterra integral equation of the first kind is developed for estimating the surface temperature using a calibrated system (host material and sensor). Sensor characterization, explicit sensor positioning and thermophysical properties are implicitly contained in the new calibration integral equation. The calibration integral equation displays only four terms; namely, the measured front surface temperature and corresponding measured in-depth temperature response associated with the calibration run; and, the unknown surface temperature and its measured in-depth temperature response associated with the second run. Preliminary numerical results indicate the merit of the concept. This paper suggests using thermographic phosphors for estimating the surface temperature in the calibration portion of the process owing to their rapid thermal response, good surface thermal contact characteristics and lack of capacitance for assuring minimal delay. Though the present paper describes the theoretical basis for resolving such problems, it is intended for near-term application using the UTK s high-heat flux laser facility which is presently under development
Progress towards fielding luminescence-based temperature measurements for the Versatile Affordable Advanced Turbine Engine (VAATE) program is described. The near term programmatic objective is to monitor turbine vane temperatures and health by luminescence from a rare-earth doped thermal barrier coating (TBC), or from a thermographic phosphor layer coated onto a TBC. The first goal is to establish the temperature measurement capability to 1300 C with 1 percent uncertainty in a test engine. An eventual goal is to address rotating turbine blades in an F135 engine. The project consists of four phases, of which the first two have been completed and are described in this paper. The first phase involved laser heating of a 2.54-cm-diameter test sample, coated with a TBC and a thermographic phosphor layer, to produce a thermal gradient across the TBC layer similar to that expected in a turbine engine. Phosphor temperatures correlated well with those measured by long wavelength pyrometry. In the second phase, 10x10- cm coupons were exposed to a jet fuel flame at a burner rig facility. The thermographic phosphor/TBC combination survived the aggressive flame and high exhaust gas velocity, even though the metal substrate melted. Reliable temperature measurements were made up to about 1400 C using YAG:Dy as the thermographic phosphor. In addition, temperature measurements using YAG:Tm showed very desirable background radiation suppression.