Feasibility Experimental Study On Steam Wetness Measurement By Ultrasonic Sensor

Wet saturated steam is the main working medium of PWR nuclear power plant.The wetness of steam will directly affect the safety and economy of steam over-flow equipment such as steam turbines,steam pipes and valves.The existing wetness measurement methods themselves has many defects,such as thermodynamic method and tracer method can’t achieve online-measurement,the adaptability of optical method is poor,the measurement accuracy of the microwave method is insufficient,and the ray method is complicated to operate,and the safety requirements are high.Therefore,it is of great significance to propose,study and verify a new wetness measurement method that meets the requirements of modern engineering measurement.In view of the strong correlation between the sound velocity of the medium and the wetness of the two-phase flow,this paper proposes a two-phase flow wetness measurement scheme based on the ultrasonic velocity detection method.Firstly,the micro-pressure disturbance equation of one-dimensional fluid is taken as the starting point,and the motion characteristics of acoustic waves in single-phase fluid medium are briefly analyzed.On this basis,for the complex two-phase flow medium,the initial theoretical model of the sound velocity method wetness measurement scheme is proposed by introducing some reasonable assumptions.Theoretical analysis and calculations show that,for wet saturated steam,the medium wetness is only a function of two direct variables of sound velocity and temperature.The overall structure of the wetness measurement model is relatively simple.The feasibility of the ultrasonic wetness measurement scheme at the theoretical level is preliminarily verified.In order to further verify the feasibility of this scheme,we design and build an acoustic wave two-phase flow wetness measurement experimental system.The experimental results show that: with the increasing of wetness,the sound velocity gradually decreases,and the two have a strong linear relationship,the sound velocity changing is about 22m/s in the wetness range of 0~20%.Based on the experimental research,this paper uses the CFD method to study the influence of the temperature and pressure parameters on the sound velocity.The results show that the sound velocity of the medium increases with the increasing of temperature.The speed of sound is linear with temperature.The speed of sound increases with the increasing of pressure.Finally,the saturated steam is taken as the research object.The effects of two-phase flow wetness,temperature and pressure parameters on the sound velocity are studied by CFD.The research results show that with the increasing of steam wetness,the sound velocity is gradually reduced,and the two exhibit a relatively obvious linear relationship.Quantitatively,the amount of sound velocity changes is greater than 50 m/s,which indicates that the sound velocity is sensitive to wetness changes.Based on the above experimental and numerical simulation results,we believes that the sonic velocity steam wetness measurement scheme based on ultrasonic detection technology has some feasibility and is worthy of further research.