Propagation Model And Characteristics Of Ultrasound In Gas-Solid Two-Phase Medium

Gas-solid two-phase media widely exist in the fields of energy,chemical industry and metallurgy.It is of great significance to achieve online measurement of particle size for the safe and economical operation of the system,energy saving and optimal control.Ultrasound has been widely concerned due to its advantages of excellent directivity,strong penetrating power,non-contact and can be transmitted in opaque media.In this paper,the ultrasonic propagation model and characteristics in gas-solid two-phase medium have been studied through the combination of theory and experiment based on the monitoring of pulverized coal particle size in power plant,which provides a theoretical basis for the development of reliable particle size measurement system.The main research results are as follows:(1)This paper simplifies the gas-solid two-phase model and changes the uncontrollable distribution of the solid particles in the gas phase into a controllable distribution,the dense phase system is simulated by natural accumulation of small particles,the dilute phase system is simulated by layered large particles,and proposed correction coefficient to solve the problem of uneven concentration.The acoustic attenuation and the velocity of sound were numerically simulated with the variation of particle size based on the expended coupled phase model and Rayleigh scattering model.In the range of 50?m~1000?m,with the increase of particle size,the sound attenuation decreases first and then increases,the sound velocity increases and approaches the speed of sound in the air.(2)The piezoelectric transducer simplified model was established and the finite element analysis of piezoelectric ultrasonic transducer was carried out.Structure and frequency domain characteristics of the transducer were simulated.It is suggested that the driving frequency of ultrasonic transducers should be higher than its characteristic frequencies in workplaces with large wear level,such as pipelines in power plants.(3)The ultrasonic measurement experiment system was built according to the theoretical model and the characteristics of ultrasonic transducer.The glass beads were used instead of pulverized coal to study the relationship between sound velocity and sound attenuation coefficient as a function of particle size.The results show that in the range of 50?m?300?m at the natural state of accumulation,with the increase of particle size,the sound attenuation decreases when the frequency is 22KHz,the sound attenuation at the frequency of 40KHz decreases first then rises slightly when he particle size is 250?m,the sound attenuation at the frequency of 75 KHz decreases first then increases after the particle size is greater than 180?m,but the sound velocity increases.The trend is consistent with the simulation results.Sound attenuation measured in stratification is smaller than that in natural accumulation at equal particle sizes,mainly because the structural attenuation and scattering attenuation in natural accumulation are greater than that in stratification.