Improvement Research On The Thermal Gas Mass Flowmeter

The thermal gas mass flowmeter can simplify the nuclear electrometer control measurement system and improve the safety and stability of nuclear power plant operation.The defects of thermal mass flowmeter are as follows:temperature,humidity,velocity distribution of flow field and the variation of gas physical parameters including thermal conductivity,viscosity and density all affect the measurement accuracy of the flowmeter.Based on the joint research and development project of domestic hot gas mass flowmeter in a nuclear power plant,this paper proposes effective methods to improve the performance of the hot gas mass flowmeter in view of the influence of temperature,humidity and flow velocity distribution on its measurement.The main work and innovation points of this paper are as follows:1)The types,principles and characteristics of current nuclear power plant flow meters are fully understood.Based on fluid mechanics and heat transfer,the working principles of thermal gas mass flow measurement are studied and analyzed.2)A temperature compensation method is proposed.The method constructs a polynomial mathematical model of thermal gas mass flowmeter characteristics.Based on the model,the least square fitting of the measured data of the flowmeter is carried out to obtain the functional relationship between the temperature and the characteristic curve coefficient of the flowmeter and complete the temperature compensation.This method further reduces the influence of temperature on the measurement accuracy on the basis of the original analog circuit temperature compensation.The experimental results show that this method can effectively improve the measuring accuracy of the flowmeter.3)A compensation method for temperature and humidity of thermal gas mass flow measurement based on improved PSO-BP neural network is proposed.The test experiment shows that this method can simultaneously compensate the influence of temperature and humidity on flow measurement and improve the accuracy of flow measurement.4)A multi-sensor measurement method based on the minimum mean square error adaptive weighted data fusion algorithm is proposed.The position of each sensor is determined by the log-linear method,and the data is preprocessed according to the relative distance method to eliminate the failure data.The experimental results show that this method can effectively avoid the influence of the irregular flow velocity distribution of incomplete developed pipe flow on the measurement of the mass flow rate of hot gas,and can effectively improve the performance of the flowmeter.