| In recent years,it is more and more important for China to develop high parameter units and realize efficient and clean coal-fired power generation.For the power plant units with high parameters,the steam pressure will drop to a very low level after thermal cycle,which is in the state of wet steam two-phase flow.The humidity of wet steam is very important to the safety,stability and economy of steam turbine.Based on this background,combining the monitoring of wet steam humidity parameters with the research direction of the research group,an acoustic method for steam humidity measurement is proposed.Based on the research content of the measurement of wet steam humidity by acoustics,this paper mainly studies the relationship between the sound velocity and attenuation coefficient and steam humidity.The first part is based on the study of the propagation characteristics of ultrasound in wet steam gas-liquid two-phase flow.Because the attenuation of sound wave in the medium is more obvious in the high-frequency ultrasonic section,and the attenuation of audible sound in the medium is smaller.Therefore,this paper selects the ultrasonic frequency band to study the influence of sound attenuation on humidity in wet steam.According to the flow characteristics of two-phase flow and the influence of physical parameters,the appropriate ultrasonic calculation model(ecah model)is selected.According to IAPWS-IF97 standard,the physical parameters of wet steam are obtained.The influence of temperature,droplet size,humidity and ultrasonic frequency of wet steam on ultrasonic attenuation coefficient is calculated.Using COMSOL software,the sound pressure distribution and attenuation of wet steam medium under different humidity parameters are simulated from another point of view.The simulation results are consistent with the numerical calculation results.The results show that different factors have different effects on the sound attenuation.The influence of steam humidity and droplet size on the sound attenuation coefficient is obvious.The relationship between steam humidity and sound attenuation coefficient presents a positive linear correlation,which provides a good theoretical support for the sound attenuation in medium to deduce the steam humidity.In the second part,the relationship between sound velocity and steam humidity in wet steam is studied.It is found that there is a one-to-one linear relationship between steam humidity and sound velocity in two-phase flow.On the basis of theoretical analysis,the steam velocity measurement method is used to verify the theory.Considering the flow characteristics of wet steam and the large space wet steam area which needs to meet the conditions when measuring the velocity of sound,the self condensation law and state change of wet steam in large space are simulated.Based on the limitations of the simulation results and the actual wet steam environment,an alternative scheme is proposed for the feasibility experimental study,and the water content in wet steam environment is simulated by the velocity of sound method The experiment of quantity proportion.The experimental results show that with the increase of humidity,the sound velocity decreases gradually,which is basically in linear relationship,which is consistent with the theoretical calculation results.Finally,some suggestions and future work are put forward for the application of acoustics in the measurement of steam humidity. |
