Research On Micro-flow Measurement Technology

Micro flow metering is widely used in many occasions.With the rise of new energy vehicles,the market share of methanol fuel vehicles is increasing year by year.Methanol fuel is made of gasoline and methanol according to a certain proportion.If the proportion of methanol in gasoline fuel cannot be accurately controlled,the use of this fuel will lead to unconventional emissions of unburned methanol from automobile engines.And other harmful substances to human body,and the control of methanol proportion needs to realize the measurement of methanol micro flow.At present,the flowmeter for measuring methanol micro flow generally has the problems of low accuracy,large linear error,low lower limit and so on.Therefore,this paper focuses on the research of micro flow measurement.In order to improve the accuracy and lower limit of micro flow measurement by flowmeter,based on CFD simulation technology,the influence of structural parameters of differential pressure flowmeter and impeller flowmeter on measurement results is studied.Through comparison and analysis,differential pressure flowmeter is determined as the flowmeter for micro flow measurement.The standard device for measuring micro flow is established,which mainly realizes the precise control of solenoid valve switch and the output setting and acquisition of current signal of the meter to be inspected.Finally,the experimental prototype of differential pressure micro flowmeter is made according to the CFD simulation results,and the water flow experimental research is carried out.The final simulation data are compared,and the results show that the trend is consistent with the CFD simulation results.The main research results are as follows:(1)Based on CFD simulation,the influence of the structure parameters of differential pressure micro flowmeter and impeller flowmeter on the measurement performance is analyzed.Through comparison and analysis,the scheme suitable for measuring micro flow is determined.The scheme can realize the measurement of flow range of 50 m L/h ～ 600 m L/h,and the linear error of corresponding instrument coefficient is less than 5%.(2)A verification device of micro flow is designed.The device adopts the principle of static weighing method to realize the verification of the meter in the flow range of 10 m L/h～ 600 m L/h.The expanded uncertainty of the device is 0.12%.(3)According to the analysis of the simulation results of the differential pressure flowmeter,the experimental prototype of the differential pressure flowmeter is made,and the real flow test is carried out.The results show that the trend is consistent with the CFD simulation results,the flow measurement can be realized in the flow range of 10 m L/h ～600 m L/h,and the linearity error of the instrument coefficient is less than 3% in the flow point of 240 m L/h ～ 400 m L/h.