Measurement of Coating Thermal Properties via Induction Phase Radiometry
This research introduces a new method for in-situ measurement of the thermal resistance of thermal barrier coatings (TBCs), used in gas turbine engines. Current techniques are complex and cannot be performed in-situ with sufficient accuracy. The proposed method involves periodic internal heat generation inside the airfoil in the vicinity of the TBC-alloy boundary using low frequency modulated induction heating through a coil. The phase-lag between the radiation flux emitted to the surroundings from the exposed side of the TBC and the recorded voltage input to the modulated induction coil is proportional to the thermal resistance (L^2/α) of the thin film. A simplified analytical model is developed to quantify the relationship between the lag as a function of the thermal resistance and induction modulation frequency. Numerical experiments are conducted to solve the full physics. Comparing the output with the simplified model, precision of 0.8% under ideal conditions can be observed. The robustness of the methodology is characterized for differing levels and types of noise levels, including Gaussian and constant lag biases. For the relevant application, it is found that the suggested approach maintains a recovery error bound to range of 1-10%, dependent on input noise level and thermal resistance. Experimental demonstration was conducted showed proof-of-concept yielding transient heating results of the specimen coating surface area, Results of the experiments fit well with simulations and the expanded analytical relations are presented together with its limitations.
The work is towards PhD degree under the supervision of Prof. Beni Cukurel, Turbomachinery and Heat Transfer Laboratory, Technion