Deposition rate sensor development project. Final report

The objective of this research project was to develop a sensor capable of real time, in situ detection of the rate of deposition of suspended particles on the surface of gas turbine components for systems utilizing coal-derived fuels for combustion. Of the several methods investigated, the system based upon correlating the thickness of the deposit layer with the amount of heat transfer to the sensor surface offers the most advantages for high-temperature, high-pressure field applications. A commercially available sensor consisting of thermopile imbedded in a ceramic filler was tested at temperatures up to 260/sup 0/C (500/sup 0/F) with fly ash deposits at surface loading levels up to 33 mg/cm/sup 2/. The output of the sensor decreased as the loading of particulate increased, and was shown to be a function of the flow velocity and the temperature of the gas stream. Radiation heat transfer effects are significant at higher temperatures. The ceramic materials of construction coupled with the thermopile design provides a robust element which can withstand high-temperature operating conditions more reliably than other methods tested or identified in the literature. The maximum particulate surface loading which can be detected is a function of heat leakage into the sides of the sensor and can be extended by increasing the thermal insulation surrounding the sensor when installed in the test section. Within the operating range of particulate loadings, the sensor had an average output of 0.043 mV/(mg/cm/sup 2/) which was independent of velocity for flow speeds below 5 m/sec. Therefore, the rate of deposition can be determined reliably over time even though the actual deposit thickness may not be known for a sensor whose calibration is uncertain due to differences in manufacture or system effects at the site of installation. 45 figs., 9 tabs.