Fabrication and Characterization of an Ag–AgPd Thick-Film Thermopile Heat-Flux Sensor for High-Temperature Applications

High-temperature metallic surfaces in aero-engine hot sections and related thermal systems are subjected to MW/m2-level heat-flux loads and transient thermal conditions, creating a need for sensors capable of quantifying heat flux under high-temperature conditions. This study aims to develop a screen-printed Ag–AgPd thick-film thermopile heat-flux sensor (HFS) for MW/m2-level heat-flux measurement on high-temperature metallic surfaces. Its main feature is the integration of an Ag–AgPd thermopile sensing layer, an insulating layer, and a thermal-resistance layer on a SUS430 stainless-steel substrate through a screen-printing-based multilayer fabrication route. Microstructural characterization, annealing condition comparison, laser comparison calibration, repeated loading, dynamic-response testing, and flame-heating testing were conducted to evaluate the sensor structure and performance. Under laser comparison calibration, the sensor achieved a MW/m2-level calibrated heat-flux response over 0.32–1.37 MW/m2, with a near-linear output relationship of R2>0.998, a sensitivity of 2.67 μV/(kW/m2), a nonlinearity of 1.83%, a hysteresis error below 0.29%, a repeatability error below 0.43%, a sample-to-sample consistency error of 1.06%, a maximum accuracy-test deviation of 1.84%, and a maximum repeated-loading stability error of 1.33%. The sensor also exhibited a time constant of 0.806 s under laser step excitation, and the baseline-corrected equivalent heat-flux response remained stable during approximately 120 s of flame heating at about 800 °C. These results indicate that the proposed HFS provides a feasible thick-film thermopile sensing approach for MW/m2-level heat-flux measurement on high-temperature metallic surfaces.