Study On Particle Concentration Characterization In Gas-solid Two-phase Flow By Ultrasonic Methods

The on-line measurement of gas-solid flows parameters is of great importance forunderstand the nature of two-phase flows and safety, economic operation of industrialprocess. Compared with Several existing measurement methods, ultrasonic method hasadvantages of strong penetrability, simple structure and environment-friendly. For moreinformation, experimental study of gas-solid flows concentration measurement byultrasonic method has been done in this paper.First of all, it present a particle size and concentration measurement method basedon the principle of ultrasonic attenuation at two different frequencies. To prove theeffectiveness of the method, experiment system was designed and the system can bedivided into hardware and software. The hardware consists of pulse generator device,signal processing device, high speed data acquisition card (NI USB-5133), transducers,experimental vessel and computer et al. The software consists of data acquisitionprogram, Spectrum analysis program, particle size and concentration calculationprogram. All of their programs were developed based on LabVIEW.Second, as a theoretical basis, the simplified ECAH model in long-wavelengthrange is employed to predict the attenuation. With the help of a gravity transport device,experiments of air-coal flow are carried out to measure the particle mean size andconcentration, in which ultrasonic signal has been generated and receiver by transducerswith fixed frequencies of100and200KHz. The ultrasonic measurement results arecompared with image processing measurements and given concentrations, which showthat the present method possesses a good foreground for the on-line measurement ofparticle concentration.Third, double-frequency ultrasonic method can only get local concentration of themeasured particle two-phase flow and the2D or3D distribution of flow parameterswhich characterize the measured two-phase flow, is often needed in many operationconditions. Process tomography techniques can provide a2D or3D image of two-phaseflow over a cross-section of pipe with many advantages. The transmission-modeultrasonic process tomography system has been developed in this paper. The systemconsisting of a sensor array with a high speed Date Acquisition Card (DAQ) and signalprocessing devices with switching device. The sensor array contains8ultrasonictransducers and each transducer can emit fan-shaped beams with angle as large as150 degree. A personal computer is used for recording experimental data and communicateswith the other device as a host. By implementing a LabVIEW-based program it cansynchronously acquire the real-time data of8channels of the DAQ Cards (PCI8501),where the multiple-channels switching device with Microprogrammed Control Unit(MCU) is of utmost importance for real-time measurements. The system can work wellin one transmitting&multi-receiving mode in which the attenuated ultrasonic wavesfrom the transmitting transducer can be received by other transducers simultaneously.Forth, a series of experiments have been done to test the system. At the first, aPTFE rod is used to simulate high concentration solid particle and which different size,different location represent different two-phase flow condition. The transducers arraycan help get all projection information at different observe angle. The cross-sectionimage of sample vessel under investigation can be reconstructed using the improvedtwo-value logic back-projection algorithm with the projection data. Compare withpreset conditions, imaging accuracy is good. Finally, measured the particleconcentration of air-coal two-phase flow on-line used this system. From thereconstruction image of the air-coal flow cross-section, the system can identify thedistribution of coal powder, but it can`t get accurate concentration distribution of coalpowder and the flow speed is limited.