Study On The Key Technologies Of Thermal Gas Mass Flowmeter And Rotameter

Thermal gas mass flowmeter has the advantages of wide measurement range,small pressure loss,high reliability,can measure the gas mixture,applicable to all kinds of pipes and overload would not be damage etc.And the rotameter has the advantages of high reliability,simple structure,low cost,wide application,etc..Therefore the thermal gas mass flowmeter and the rotameter are widely used in industrial measurement.However,when the parameters of measured fluid changing,the performance of flowmeter is changed inevitable,which cause a large measurement error.In this paper,the effects of fluid viscosity on the rotameter and the heat transfer of thermal gas mass flowmeter for sheathed probe is studied.The author concretely did the following work:1.A new measurement method of constant current for thermal gas mass flowmeter was proposed.According to the principle of heat transfer theory,the principle of the constant current method was analyzed,and the measurement model was derived.The measurement model and the arrangement of probe were determined by the theory of fluid flow across the double tube and the mixed convection heat transfer theory respectively.Then a prototype was developed,and the heat transfer performance of the thermal gas mass flowmeter by constant current method was studied by experiment under different temperature.2.A three-dimensional heat transfer model of sheathed probe was established,and the formula of temperature compensation was deduced.Then the effectiveness of the temperature compensation was verified by experiment.The error between experiment and measurement model was analyzed.Finally,the measures are proposed to reduce the error and improve the measurement performance of thermal gas mass flowmeter.3.The effects of fluid viscosity on the rotameter was analyzed by the simulation method.The effects of fluid viscosity on DN50 orifice rotameter and DN80 cone rotameter were simulated by CFD software.The simulation scheme and model of cone and orifice rotameter were established through the analysis of the flow Reynolds number,mesh and turbulence model.The simulation results were analyzed,and the rationality of the simulation was proved through compared with the viscosity experiment.The key parameter of the viscosity effect on orifice rotameter-the diffusion angle of jet flow and the key parameter of the viscosity on the cone tube rotameter-vortex size were studied by analyzing the simulation results.And the experience formula of the diffusion angle of jet flow numerical was summarized through extracting the flow rate of simulation results.4.The viscosity corrected model was established.The orifice rotameter force model in the measurement of viscous medium was established by use of the theory of concentric annulus laminar flow and the wall jet theory.The cone rotameter viscosity correction model was established by adopting the theory of vortex and the theory of concentric annulus laminar flow.The validity of the correcting model was verified by experiment.This method breaks through the limitation of traditional viscosity correction method,and improves the accuracy of measurement results.