Universality Research Of Different Media For Thermal Gas Mass Flowmeter

At present,the global market trade and product transportation settlement are settled by quality.The thermal gas mass flowmeter has been widely concerned with its advantages of high sensitivity,high stability and high reliability.The thermal mass flowmeter can measure the mass flow of the medium based on the heat exchange principle.However,the existing method uses a single gas real-flow calibration mathematical model,and does not consider the influence of the gas physical property parameter in the model,so it can only measure the same gas.Aiming at this problem,this paper reveals the concrete form of physical parameters of medium in the model by theoretical method,and determines the functional relationship between physical parameters and output of thermal flowmeter by means of experiment and data processing.The mathematical model can be applied to different gas measurements to improve the universality of thermal mass flowmeter.The main research contents are as follows:(1)Based on the principle of heat exchange,this paper takes the platinum film heat gas mass flowmeter of constant power type as the prototype.The mathematical measurement models of laminar and turbulent flow states are established,and the relations between the velocity u of medium,gas physical property parameter μ,Cp,γ,p and the output temperature difference ΔT are obtained.Laminar flowΔT=Nμ-1/6cp1/3γ2/3(ρu)1/2,turbulent flow:ΔT=Mμ-7/15cp1/3γ2/3(ρu)4/5,mass flow M=ρuS,mass flow is obtained through temperature difference.(2)In laminar and turbulent flow,the flow coefficient and physical property parameter index in the measurement model are constant.The theoretical results show that when the flow state and velocity are determined,only the physical property parameters of the medium affect the measurement results of the sensor.If the physical property parameter index and the velocity index are accurate,the model can be used for any gas measurement.In this paper,the least square method is used to design the correction scheme.(3)In this paper,a double-precision real flow calibration device was designed,which was combined with standard table method and volumetric method.This device was used to conduct a variety of gas experiments to provide reliable data for model correction.Since the built-in rectifier in the checklist is measured in the laminar flow state,this paper only corrects and verifies the laminar flow mathematical model,and uses gas data to modify the physical parameter indexes a,b,c and flow index u of the laminar flow mathematical model,and finally uses new gas for verification.Through the above research,the verification results show that the relative error of the mathematical model is 5%,which proves that the modified laminar flow measurement model can be used for the flow measurement of different gases under laminar flow conditions.By inputting the physical property parameters into the measurement model,different gases can be measured,and the application range of the constant power type thermal gas flowmeter is expanded.