The Low Frequency Ultrasonic Test Research Of Meso And High Concentration Gas-solid Two-phase Flow Of Fly Ash In Conveying Pipe

The meso and high concentration pneumatic conveying has been widely applied for the advantages of low power consumption, stable operation, easy to realize automatic control.And the corresponding research of experiment and theory also got great progress. For the test of meso and high concentrations of gas-solid two-phase flow parameters has been people focus on by esearch workers. According to the characteristics of the two phase flow, it has formed many test methods such as optical method, electrostatic measurement, ultrasonic measurement, and other test methods. The ultrasonic measurement has been one of the most important methods of meso and high concentration gas-solid two phase flow because of the good penetration performance, stable performance, the easy realization of on-line monitoring and other characteristics. However, how to reduce the ultrasonic frequency and how to deal with the ultrasonic signals to get two phase flow parameter have become the bottleneck that restricted its further application.This article chooses the top fluidization warehouse pump as sending device, conveying with compressed air as a driving force and the fly ash as conveying material. In order to get flow parameters, the low-frequency ultrasonic test platform has been built. The platform including ultrasonic generator, ultrasonic trap and signal acquisition processing equipment. In the experiment, a air single-phase flow experiments was taken firstly, to get ultrasonic signals in single-phase flow. And then it will be the standard for signal processing to get the ultrasonic attenuation coefficient under different flow state. The fast Fourier transform on the ultrasonic attenuation coefficient, was carried as inversion computation to get concentration of solids in the pipe. At the same time, the short-time Fourier transform of the ultrasonic signal was taken to get the corresponding solid conveying velocity.According to the needs of the experiment research, the ultrasonic wave propagation was analyzed through the angle of quality, energy and momentum conservation based on the ultrasonic attenuation mechanism,such as viscous losses, absorb losses and heat loss, etc.,and physics and related acoustic basis,and the characteristics of gas-solid two phase flow. Then the ECAH model and the simplified McClements model which are suitable for the working condition are gotten.The ultrasonic will come up scattering loss when it come through the fly ash particles,then the attenuation was created. According to various physical parameters of solid phase particles and ultrasonic spectrum,the BLBL model which is suited to the working conditions.Thus, this this article selects the superposition of McClements model and BLBL model to deal with ultrasonic signal.The experimental research can get ultrasonic signal which contains two phase flow information. The solid concentration and solid velocity and its change rule under different apparent gas velocity can be gotten.At the same time,the solid quality change can be detected by using electronic weighing instrument,which combine with the result of vortex flowmeter solid concentration change rule can be gotten. The change rule of solid velocity can be obtained by the differential pressure transmitter monitoring and the static pressure transmitter monitoring,the theoretical relevant expression between the characterization of fly ash and main conveying characteristic parameter has been analysed with dimensional analysis method and mathematical analysis method based on massive data which are gotten from the test.. At last,the rusults obtained by ultrasonic test and two other methods were contrastive analyzed.Studies have shown that the results of ultrasonic test and other two methods have good similarity.The fly ash conveying velocity will increase with the increase of gas superficial velocity, the concentration of the fly ash will be increased with the increase of gas superficial velocity presents first then decrease.The Paper has systemly studied the change law of pressure drop along pipeline, and its correlation with solid concentration and gas superficial velocity. The studies have shown that at the starting stage, the gas superficial velocity is the dominant factor on the changes of pressure drop, pressure drop will increase with the increase of gas velocity. When gas velocity enter the high speed area, the pressure drop will decrease after a short balance.And the change rule is similar to the change of solid concentration. At this time, concentration change has become the dominant factor of the pressure drop.The paper is trying to detective the Meso and High concentrations of fly ash using ultrasonic testing device as a innovation exploration.The parameters gotten with the ultrasonic testing device were compared with the data gotten with other testing method. The result showed that ultrasonic testing have a good similarity with the normal testing method.Thus,ultrasonic testing technology can be applied in the monitoring of meso and high concentration pneumatic conveying.