Design And Realization Of Wide-temperature And Wide-humidity Thermal Mass Flowmeter

With the rapid development of the environmental protection industry,the control of flue gas pollutant emissions has become an important measure in the environmental protection management for our country.Accurate measurement and control of flow play an important role in environmental monitoring.Among gas flowmeters,the thermal gas mass flowmeter has the characteristics of high measurement accuracy and large measurement range.This dissertation analyzes the measurement principle,advantage and disadvantage of thermal gas mass flowmeter,in addition,designs the flow measurement scheme suitable for wide-temperature and wide-humidity flue gas combined with the practical engineering application of flue gas pollutant emissions.The main research contents of this dissertation are given as follows:(1)The model of the wide-temperature and wide-humidity mass flowmeter is given with the simulation results.The position of the temperature measurement probe is determined according to the temperature field distribution in the pipeline when the heating probe is in different positions.The relation between power consumption and temperature difference of the probes is obtained by the simulation result of the constant temperature differential measurement method,which can be used to determine the temperature difference between two probes.The relation between mass flow and power consumption with different gas temperature is analized,which can provide fundamental basis for the design of the digital temperature compensation program.These simulation results provide theoretical guidance for the engineering realization of the wide-temperature and wide-humidity thermal mass flowmeter.(2)Considering the hardware cost and development efficiency comprehensively,the hardware scheme and software scheme of wide-temperature,wide-humidity thermal mass flowmeter are designed and realized.The method of automatic heating to control the temperature of the measuring chamber prevents gas condensation and solves the effect of wide-humidity flue gas on system stability.The PID control algorithm is applied to the program of constant temperature differential type,which can improve the reliability of the instrument constant temperature differential control under wide-temperature conditions.According to the simulation results at different gas temperatures,a digital temperature compensation program is designed to solve the influence of wide-temperature flue gas on the measurement accuracy.(3)The experimental platform with a standard flow generation system is built to test and debug the module of the wide-temperature and wide-humidity thermal mass flowmeter.The mass flowmeter were installed and applied in the industry after the technical parameters of the mass flowmeter were tested and analyzed in the calibration experiment.The experimental result shows that both the repeatability and the indication error of the designed thermal gas mass flowmeter are within 2%,which meet the measurement accuracy requirements of the wide-temperature and wide-humidity thermal mass flowmeter to be applied in the industry.The thermal gas mass flowmeter designed in this dissertation can realize the gass flow measurement with expected accuracy under the premise of controlling costs of wide-temperature and wide-humidity flue gas,which will play an important role in the engineering application.