Research On The Measurement Characteristics And Compensation Method Of The Novel Thermal Mass Flowmeter

The measurement of the thermal mass flowmeter is based on the heat exchange between the velocity sensor and the fluid being measured.It is widely used in the semiconductor,energy metering,medical,aerospace and other fields because of its simple structure,wide measurement range and high measurement accuracy.The current traditional thermal mass flow meter installation requirements are high,measurement results are easily affected by the flow velocity distribution.In this paper,a novel thermal mass flowmeter that is insensitive to the flow velocity distribution in the pipe is proposed by improving the composition and structure of the probe.By means of theoretical analysis,numerical simulation and experimental testing,the measurement characteristics of the novel thermal mass flowmeter were analyzed,and the temperature and component compensation method of the novel thermal mass flowmeter was proposed and verified.The application range of the novel thermal mass flowmeter was broadened.The main work of this paper is as follows:(1)Numerical model of flow heat transfer considering axial heat conduction of the velocity probe for a novel thermal mass flowmeter was developed,which effectively improves the calculation accuracy of the numerical model.And the axial thermal conductivity of the velocity probe was calculated by the numerical model of the composite material,and a feedback adjustment procedure was used to maintain a constant temperature difference between the velocity sensor and the fluid.So that the temperature distribution on the surface of the velocity sensor is consistent with the actual temperature distribution.By comparing the simulated values of the three turbulent flow models with the measured values,it was determined that the SST k-ω model could better represent the heat transfer process of the flow in the pipe.(2)The effect of the installation method on the measurement characteristics of the novel and traditional thermal mass flowmeter was investigated by numerical simulations.When the pipe axial installation position of the velocity sensor is 120 D and 5 D,the maximum power deviation is 7.40%and 1.00%for the traditional and novel thermal mass flowmeter,respectively.When the insertion depth of the velocity sensor is l and l/8,the maximum deviation of the traditional thermal mass flowmeter is 43.30%,while the insertion depth of the novel thermal mass flowmeter is fixed and unique,so its measurement result is independent of the insertion depth.Compared with the traditional thermal mass flowmeter,the measurement characteristics of the novel thermal mass flowmeter is almost independent of the flow velocity distribution in the pipe,and the installation is more convenient.(3)Through numerical simulations and experimental tests,it was obtained that temperature variations can cause large deviations in the measurement results of the novel thermal mass flowmeter.According to the numerical calculation results,the temperature compensation formula of the novel thermal mass flowmeter was established based on polynomial fitting.The experiment of the novel thermal mass flowmeter was carried out under variable temperature conditions when air temperature ranges from 298.0 to 353.0 K.The maximum deviation of measurement results under different temperature conditions before temperature compensation is 21.97%,while the maximum deviation after temperature compensation is only 0.91%,which greatly reduces the influence of temperature on the measurement results.(4)The measurement results of the common thermal mass flowmeter will have larger deviations in the measurement of different fluid,a component compensation method is proposed in this paper,and the formula of component compensation coefficient is obtained,so that the novel thermal mass flowmeter can be used for the measurement of different fluid.Simulations were performed for carbon dioxide,hydrogen and natural gas,and the maximum deviation between the simulated and calculated power values of the three gases was less than 5%,which verified the reliability of the component compensation method and broadened the range of the flowmeter.