Gas-liquid Two-phase Flow Tomograph System Based On γ-ray CT And ECT

Gas-liquid two-phase flow, as a one common kind of multi-phase flow, exists widely in the filed of industrial processes. Process tomography is an important non-invasive tool for on-line analysis of multi-phase flows. As one type of successful process tomography, industrial computed tomography is thought to have the potential applications as an effective tool for two-phase flow measurement.A third-generation X-ray CT scanning configuration is applied to theγ-ray computed tomography system for gas-liquid two-phase flow. In order to improve the real-time performance of the imaging system, an electrical capacitance tomography system is designed here. The main work and conclusions are as follows:(1) Firstly, a brief summary is given on industrial process tomography, and then a detail discussion of the history and current status of computed tomography is presented. A fan-beam CT model based on physics theory and maths calculation is built. Meantime, a simulation using the Geant4 toolkit is carried out. The simulation model of theγ-ray CT system is established firstly, and then the physical process of scattering and attenuation during the interaction of matter and radiation is successfully analyzed. The simulation results show that theγ-ray CT with seven sources and seventeen detectors can meet the need of two-phase flow imaging.(2) A system scheme of theγ-ray CT system for gas-liquid two-phase flow is given firstly, which comprises one 300mCi 241Am source and 17 CdZnTe detector units. And then every part of the system, such as a Gaussian pulse-shaping network and a digital counter based on FPGA, is designed. TJU_CT, the visualization system software, has been designed in C++ for industrial imaging application. And some algorithms are embaded in the software, such as ART, Landweber iteration method and CG. Thisγ-ray CT system has a high SNR and a user-friendly interface with a low cost.(3) A particular system analysis is provided in the following section about basic factors which affect the image quality of theγ-ray CT scanner. And spatial resolution and photon count statistics are discussed in detail. Experiments show that a system with seven sources can fulfill the designing requirements for the on-line study of gas-liquid two-phase flow effectively. When the velocity of the dynamic model is less than 40mm/s, this system has a spatial resolution of 7mm and image rates of 33 frames per second. Limited-angle tomography is introduced into industrial CT system here, and can perform as well as full-angle tomography. And wavelet denoising technique is also used to remove noise of dynamic count, which can remove the fuzzy areas and stripes and improve the image qulity in the dynamic test.(4) An ECT system based on DSP and FPGA is designed to improve temporal resolution for two-phase flow imaging. In the system, FPGA is in charge of logical controls and digital demodulation of the signal, while DSP takes charge of reconstruction algorithms and communication with the host PC. Sensitivity matrix algorithm and Landweber iterative algorithm are used here. Experiments show that the ECT system has a spatial resolution of 10mm and image rates of 416 frames per second. At last, some experiments of dual-modality CT/ECT system are finished. And it can be concluded that theγ-ray CT system has a better spatial resolution and a worse temporal resolution than the ECT system when two-phse flow moves slowly.