Modeling And Simulation Research And Fabrication Of A Thin Flim Heat Flux Gauge

In the fields of aviation and aerospace,turbine blades as one of the core parts of aero-engine,the temperature distribution status have a direct relationship with the service life of components in normal working condition,therefore it is entirely inadequate to take the temperature as the only signal while calculating and analyzing the temperature distribution of turbine blades under badly working condition.With the rapid development of science and technology,the heat flux density survey has got sufficient attention and development,especially the measuring based on turbine blades of aero-engine.Compared with traditional heat flux gauge,the film heat flux gauge shows remarkable advantages such as good compatibility with test component,fast response speed,structure miniaturization,high sensitivity and so on,while measuring surface heat flux density of turbine blades.Thermopile heat flux gauge has been applicated in heat flux density survey widely for its wide measuring range,large output signal.In this work,a kind of thermopile film gauge is designed and prepared and its properties were investigated.The film heat flux gauge is analyzed and optimized by theoretic calculation and ANSYS simulation.Conclusions can be drawn that the output of heat flux gauge is directly related to the Seeback coefficient of a thermocouple composed the film thermopile,the thermal conductivity and thickness of thermal resistance layer material.According to simulation result,three factors can influence measurement precision using heat flux gauge on heat flux measurement.The thinner thermal resistance layer is,the longer thermal insulator layer is,the larger thermal conductivity is,the higher measurement precision could be.The results of calculation and simulation can provide reference and guidance for the design and optimization of heat flux gauge.The film heat flux gauge is prepared using thin-film depositing technology.The thermopile is patterned by photolithography lift-off process,Pt/PtRh thermopile films are prepared by RF magnetron sputtering,and the SiO₂ and YSZ thermal resistance layer are prepared by electron beam evaporation.The effect of sputtering power on film morphology,electrical properties and deposition rate are studied.The results show that with sputtering power increasing,the deposition rate increases,the resistivity decreases at beginning and then trends to stable.With the sputtering power of 120 W,Pt and PtRh films are smooth and dense,and the resistivities are 2.08×10-5Ω·cm and 3.53×10-5Ω·cm respectively,the deposition rates are 9.5nm/min and 10.3nm/min respectively,and the Seebeck coefficient is 9.4uV/℃ when calibrating the film thermocouple.Moreover,the effect of substrate temperature and evaporation beam on the surface morphology and deposition rate of SiO₂ and YSZ thermal resistance layer are studied.The results show that the SiO₂ film prepared at 250 ℃ and 50 mA of evaporation beam.is mainly kept in amorphous state and the surface of the film was homogeneously smooth.with temperature increasing,the YSZ film is transformed from non crystalline state to crystalline state,and the surface is smooth and dense at 300℃ of substrate temperature and 60 mA of evaporation beam.The SiO₂ and YSZ thermal resistance layer with different thickness and the heat flux gauge with different number of thermocouples are calibrated respectively.The sensitivity K value of the heat flux gauges with 1um-5um thickness the SiO₂ thermal resistance layer is 6.41×10-4uV（W/m²）、1.10×10-3uV（W/m²）、1.34×10-3uV（W/m²）、1.55×10-3uV（W/m²）和 1.71×10-3uV（W/m²）.The sensitivity K value of the heat flux gauges with 1um-5um thickness the YSZ thermal resistance layer is 4.72×10-3μV（W/m²）and 7.90×10-3μV（W/m²）.According to the sensitivity K value,the thermal conductivity of the thermal resistance layer is deduced.The results show that the thermal conductivity of SiO₂ and YSZ thermal resistance layer is very small,and SiO₂ and YSZ thin film is very suitable as the thermal resistance material.As the film thickness increases,the thermal conductivity of the film also increases.Comparing with the signal of the sensor at different temperatures,it is found that the signal strength increases with the increase of the temperature and the thickness of the thermal resistance layer,but the test accuracy of the heat flux gauge decreases and the drift rate increases.Compared to SiO₂,the heat heat flux gauge with YSZ thermal resistance layer has not only more stronger signal,but also more stable performance.