Research On The Influence Of Oil Pollution On Flow Measurement Of Hot Film Gas Flow Sensor

MEMS hot-film gas flow sensor has been widely used in aerospace,automotive,environmental monitoring and other fields due to its rapid dynamic response,low power consumption and small size.The ideal working medium for hot-film flow sensor is clean air or other clean gas,but the air is mixed with a lot of fine dust and oil mist particles in some occasions with harsh working environment.During the use of the sensor,particles in the gas will be deposited on the surface of the chip,which will cause the measurement accuracy of the sensor to decrease continuously with the increase of working time,resulting in inaccurate measurement and the equipment may be damaged.By studying the distribution of oil deposition on the surface,this paper analyzes the influence of the position,thickness and other paramaters of the oil pollution on the measurement accuracy of the sensor,which is of great significance to improve the measurement accuracy of the hot-film flow sensor.This paper introduces the internal structure and working principle of the hot-film flow sensor,and deduces the mathematical model of the hot-film flow sensor based on the basic principles of thermodynamics.The oil mist generating device is designed,and a pneumatic experiment circuit which can produce oil mist is set up.The PFM725 flow sensor is used to conduct a staged chip oil deposition experiment.The deposition of oil on the chip surface is analyzed,and the influence of natural oil deposition at different stages on the accuracy of sensor flow measurement is obtained.According to the oil deposition,the oil pollution model is established and simplified.The influence of location,thickness and other parameters on temperature field and flow field of sensor chip is investigated by FLUENT numerical simulation.Different types of oil deposition models are built on the surface of the chip by controlling fiber filament,and the effect of different types of oil pollution on the accuracy of sensor flow measurement is analyzed.By comparing with the results obtained from the numerical simulation,the main influencing factors of oil pollution on the measurement accuracy of the sensor are obtained.