| The real-time monitoring of the heat flux of the aircraft surface and engine is of great significance for flight safety and thermal protection design of the aircraft.The thin-film heat flux sensor has the advantages of small volume and instantaneous measurement,which can measure the instantaneous heat flow of the aircraft shell and engine under the condition of little interference to the test surface.At present,however,the thin film heat flux sensor has poor high temperature resistance and weak output signal.In order to prepare a sensor with strong output signal,high sensitivity and resistance to high temperature of 1000?,the following work is carried out in this paper around the design,preparation and calibration of thin-film transient heat flux sensor.A thin film heat flow sensor based on MEMS technology was designed.The whole structure of the sensor is designed based on Fourier theory.According to the working principle of thermopile,the output signal strength is increased by increasing the number of thermocouples in thermopile.According to Fourier's law and the formula of thermopile output potential,the method of calculating the sensitivity is deduced.According to the characteristics of the first-order heat conduction system,the calculation method of response time is derived.The materials and size of each part of the sensor were determined according to the design requirements of working temperature of 1000?,can measure 800kW/m2 heat flux,the sensor size less than13mm×13mm×1.1mm,sensitivity higher than 0.01?V/?W/m2?,instantaneous measurement and other restrictions,and the process flow of the sensor is designed according to the structure of the sensor.The encapsulation structure of the sensor was designed for the wind tunnel experiment.According to the law of intermediate conductor,the signal circuit was designed,and the intermediate conductor Ag and Cu/CuNi compensation wires were used.The sensor was fabricated by MEMS process,and the simple test was carried out after packaging.114 pairs of Pt/PtRh thermocouples with wire width of 60?m and length of 1mm were prepared by exposure and development,magnetron sputtering and stripping processes.The success rate was as high as 100%in the three batch preparation.Through radio frequency sputtering and wet corrosion process,an efficient SiO2 step thickness control method without affecting the surface quality was developed,and the thermal resistance layer with low order of1?m and high order of 6?m was prepared,and the thermal conductivity of SiO2 film was tested to be 0.92W/?m·K?.The sensor was encapsulated and the output of the sensor before and after packaging was tested.It was found that the output of the sensor after packaging was reduced by 3.6%,which verified the feasibility of the signal circuit.Moreover,the sensor was placed under the conditions of 200kW/m2 and 800kW/m2,and the measured sensitivity was 0.028?V/?W/m2?and 0.019?V/?W/m2?,respectively,which met the design requirements.The calibration equipment based on contrast method is designed for the calibration of transient heat conduction heat flux and steady state heat conduction heat flux.For the calibration of steady-state heat conduction heat flow,the heat flow can be preset by adjusting the temperature and water speed according to the given formula.Induction heating equipment is selected as the appropriate heat source.Among them,the steady-state heat conduction heat flux needs the water cooling device.According to the principle of convection heat transfer,the cooling pipeline is designed in this paper,and the equipment can calibrate 1000kW/m2 heat flux through theory. |
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