Design And Experimental Research Of Microwave Steam Wetness Measurement System And Sensor

In the process of the development of public utilities and basic industries in China,the substantial increase of coal-fired power units in the power industry has made great contributions to the previous economic development.As the main energy conversion device for thermal power and nuclear power plants,steam turbines are of great significance for their safe and economic operation.When a conventional thermal power unit or nuclear power unit is involved in peak-shifting operation,the fluctuation of the load will cause the wetness of the last few stages of the turbine to change,and the presence of wetness seriously affects the operation of the unit and the safety of the blade.Based on microwave perturbation theory,the method of measuring the wetness of the cavity can realize the real-time,continuous and high-precision measurement of wet steam.Based on the original cavity sensor design,this paper further develops and designs the sensor and its supporting measuring system.As well as optimization,the error of the measurement system,the preparation of the PC software and the influence of temperature changes on the cavity still need further study.The specific research contents of this paper are as follows:1.Wet steam wetness measurement resonant cavity sensor selects a cylindrical cavity that is easy to process and assembles easily.The working mode is TE₀₁₁ mode.Based on the working mode to determine the structural size of the cavity and its resonant frequency,the high frequency sensor design with a no-load frequency of 12GHz is theoretically determined.Coupling structure selection loop coupling,HFSS electromagnetic simulation software is used to model the cavity proportionally.The cavity coupling thickness,opening aperture,opening spacing and coupling loop penetration of the cavity with the best energy coupling are obtained through simulation optimization.Parameters such as length.The simulation results have good electrical characteristics and quality factors,which can meet the actual measurement needs.2.In order to realize the industrial application of the resonant cavity,the wetness measuring system was designed,and the measuring components were selected according to the designed measuring system.Since the system error is accumulated and inevitable by the error of each component of the system,the error of the system is optimized or corrected by analyzing the measurement system.The system standard uncertainty is determined to be 0.004%maximum and the maximum uncertainty is 0.008%,the overall integrated uncertainty of the measurement system is 0.764%.3.Labview software is used to write the upper computer software for communication with the single chip microcomputer.The supporting software receives the data transmitted from the single chip microcomputer,adopts a certain method to perform polynomial fitting on the data,and obtains the resonant frequency of the high frequency resonant cavity through analysis,thereby obtaining the Steam wetness in the cavity.4.The relationship between resonant frequency and temperature change is analyzed theoretically,and the temperature characteristics of the cavity are tested.The experimental results show that the frequency offset due to temperature change is about206.47kHz.Through the experiment of dynamic temperature characteristics of the resonant cavity,it is found that when the air temperature changes greatly,the resonant cavity reaches the equilibrium time for more than 30 min,which will affect the real-time performance of the steam humidity measurement,so the corresponding solution is proposed.Finally,the effects of factors such as oxidation of the cavity material and changes in ambient air composition on the temperature characteristics were analyzed qualitatively.