Researches On Fabrication And Properties Of Flexible Hot-film Mass Flow Sensor

The measurement of the gas flow on the surface of the aircraft has a significant impact on the performance and life of the component.It not only provides a clear diagnosis of near-wall flow and shows laminar or turbulence characteristics,but also directly relates to active control resistance.The aerospace industry(eg,aircraft wings,aero engines)has very high requirements for mass flow sensor performance(especially the device's sensitivity,stability,measurement range and so on.The traditional measurement method has the advantages of interference flow field,low test progress and slow response speed.While the flexible hot film flow sensor has the advantages of small volume,fast response speed and no interference to the flow field.In order to meet the requirements of high sensitivity,good stability and suitable for heterosexual components,a flexible hot film mass flow sensor are designed for aircraft wing surface.The preparation technology and resistance temperature coefficient of the heat-sensitive Ni film were studied.The sensitivity and calibration of the flexible hot-film mass flow sensor were studied.First of all,the dimensions of the sensor model were designed with ANSYS simulation software,including the thickness of the substrate and the spacing between the hot films.Besides,the resistances of hot film,arrangement of sensor and wire distribution were designed.The results show that the smaller the thickness of the substrate is,the smaller the heat loss is.When the distance of the hot film was constant.The measurement result is more accurate.So,the distance of the thermistor was designed with 2 mm.When the air flow velocity was constant,the distance of adjacent thermistor increases,the diffusion of heat would be less interference on each other.So the substrate thickness was 0.05 mm.When the thickness and distance of the flexible hot film mass flow sensor are constant,the heat dissipation of the adjacent thermistor decreases with the increasing of the flow rate,which is more beneficial to improve the sensitivity of the sensor.The metal Ni with high resistance temperature coefficient was used as the sensitive material and PI with high thermal insulation coefficient was used as the substrate.The flexible hot film mass flow sensor was prepared by combining the hard mask technology with the microelectromechanical processing technology.By studying on the preparation process of sensor,the sputtering power was 120 W,the pressure of argon gas was 0.6 Pa and the thickness of the film was about 1 ?m,the resistance temperature coefficient was the largest.A relatively high resistance temperature coefficient was measured with a TCR value of 4.41x10-3 /?.Secondly,the output voltage of the hot film mass flow sensor at different wind speed was measured with the wind tunnel test.The larger the air flow velocity was,the greater the output voltage of the thermistor was.When the wind speed reached 30 m/s or more,the air flowed from the laminar flow state to the turbulent state.When the air flow rates was less than 30 m/s.The sensitivity of the sensor was 0.388 V/Pa and the maximum error of the non-linearity was 1.2%.At the same time,the calibration of the sensor was carried out.The results show that the linear relationship between the airflow velocity and the output voltage was good and the sensitivity was high.The mass flow rate and shear stress measurement of the wing surface could be realized at the speed of 0~30 m/s.