Investigating Multi-Phase Pipe Flow Measurement Technology Based On γ-Ray

Since the multiphase flow broadly exists in nature and industrial process, the measurements of fluid dynamics parameters are of great significance in both scientific research and engineering. The subject of this thesis is oil/gas/water multiphase flow, and online measurement of multiphase flow based on low-energyγ-ray radiation is mainly studied. Fluid dynamics parameters, like phase fraction and fraction phase flux, on each cross-section of the detecting pipeline are obtained using direct or indirect methods, and real-time images are provided.This project is mainly focused on the design of the hardware system, the image reconstruction software package and the novel reconstruction algorithms. The following researches are conducted and the corresponding results are listed below.1. Optimization of the hardware design of the multiphase flow online measurement systemBy the analysis of the factors influencing the online multiphase parameters and the simulations of sensing system by Geant4, the hardware configuration is designed. This research mainly consists of four parts: the design of the hardware system for Gamma-Ray tomography, the CdZnTe semiconductor detector arrays, the signal processing unit for the output of detectors, and the data acquisition sub-system based on FPGA.2. The Design of Signal Processing UnitThe flow state of oil/gas/water multiphase flows is relatively complex and the measurement ofγ-ray is of randomization and statistical fluctuating property in itself. Considering that the output signal of the semiconductor detectors is too weak, it can hardly be measured accurately by normal signal processing units. Based on the analysis of the measurement noise, the research on detecting the weak output signal and filtering the measurement noise and etc. is studied in the thesis. A method with respect to the weak output of the CdZnTe detectors is proposed. 3. The development of online measurement software system used in the multi-phase systemBased on 32 digit Windows platform, the real time imaging system (CT_SystemII) is designed using Visual C++ 6.0. There are six functional units: the calibration unit, the measurement unit, the serial communication unit, the algorithm implementation and application unit, the imaging visualization unit, and the data storage and replay unit. With the CT_SystemII, the calibration and measurement of flow parameters can be realized, and additionally the cross-sectional images of the phase distribution can be displayed online.4. Research on imaging reconstruction algorithmsHaving an insight into the research of the filtered back projection method and iterative method, a new iterative algorithm based on filtered back projection is proposed. This algorithm combines the filtered back projection method with iterative method, applying the results of the filtered back projection as the initial guess for iterations. Simulation results show that the proposed method can improve the quality of reconstructed images with high speed which can meet the requirements of real-time measurement. Another image reconstruction algorithm, bidiagonalization algorithm, is also proposed in the thesis. Results indicate that this algorithm can reach the satisfactory accuaracy with less time.Finally, the suggestion of the further applications of nuclear technology to the online multiphase detection device is put forward at the end of this thesis.