Temperature Modulation Method for In-situ Measurement of Surface Temperature & Emissivity

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For materials at high temperature, the emitted spectrum of electro-magnetic radiation is the most convenient non- intrusive probe of temperature, if the spectral emittance of the material is known, and if the emitted radiation can be distinguished from extraneous radiation which is reflected or scattered. The Phase I program demonstrated that many of the problems of in-situ temperature and emissivity measurement could be overcome by a technique which modulates the temperature of the hot surface of interest at the point at which the emitted spectrum of electromagnetic radiation is being monitored. By modulating the temperature, it is possible to distinguish emitted from reflected radiation. Routine calculations involving the observed spectrum of modulated radiation can then be applied to determine both the temperature and emissivity. Phase I demonstrated the measurement of temperatures to within > 1 K for surfaces of known emissivity and temperatures to within > 15 K and emissivity to within >7% for surfaces with unknown emissivities. For this Phase II project, we will complete the research which will allow us to design, build, test, calibrate and field test a research prototype system based on an FT-IR spectrometer and a CO2 laser to modulation the frequency. We will improve upon the Phase I apparatus by: 1) decreasing the measurement uncertainty by modulating the temperature in sequence with the FT-IR spectrometer to eliminate problems of long term drift; 2) reduce measurement noise by using a more sensitive detector; 3) extend the high frequency limit to accommodate higher temperature surfaces; and 4) make the system user friendly and automated. The target specifications for the system will be as follows: temperature measurements for surfaces of known emissivity to within > 0.25>C; temperature measurements for surfaces of unknown emissivity to within > 5>C; and emissivity measurements for surfaces of unknown emissivity to within > 2%. The system will be field tested in a coal combustion pilot plant.