Flow Characteristic Analysis Of Gas/liquid Two-phase Flow Based On ECT

The Two-phase flow system widely exists in many industrial control processes, like the petroleum, power and chemical engineering. Researches on the hydrodynamics, mechanisms and the interaction of different phases, the identification of flow regimes, and the accurate measurement of flow parameters for two-phase flow are of great important. Flow characteristics and the real time measurements of flow parameters for two-phase flow, such as void fraction and velocity estimation, are greatly influenced by flow regime; therefore the acceptable flow regime identification results and the characteristics analysis of two-phase flow become an important issue.Based on the capacitance measurements data directly obtained from electrical capacitance tomography (ECT) system on horizontal pipe, which contain flow regime information, the theoretical analyses and experimental studies were conducted in this paper; signal processing methods, such as nonlinear and time frequency analysis, were employed to realize the flow regime classification and properties analyses. The main works and results are briefly listed as follows:1. By the higher-order statistics technique, bispectrum and bispectrum diagonal slice analysis of the capacitance measurement data were firstly conducted, and the energy and amplitude information were reorganized as a feature vector. And then, combined with fuzzy cluster algorithm, a flow regime classification method was proposed. In addition, based on the third order cumulants analysis, the non-Gaussian and nonlinear properties of measurement were briefly discussed. Furthermore, by the bispectrum diagonal slice analysis, the phase coupling phenomenon was verified, and the fundamental frequency and the harmonic frequency were estimated.2. Nonlinear information processing methods were mainly adopted to analyze the characteristics of gas/liquid two phase flow. According to the Cao method (embedding dimension determination algorithm), it was analyzed that the measurement data of two-phase flow is a composite of stochastic component and determinate component qualitatively. Secondly, the nonnegative largest Lyapunov exponent shows the chaotic characteristic of measurement for two-phase flow, thereby it can be concluded that the two-phase flow system has chaotic properties. Finally, through the calculation of chaotic parameters, like correlation dimension, Kolmogorov entropy and multiscale entropy, the quantitative and qualitative analyses were conducted respectively for gas/liquid two-phase system, which can not only provide usefully information for flow regime identification, but also can reveal the essence properties for different flow regime. As shown in the experiments, all those nonlinear analysis methods can disclose the inner characteristic of two-phase flow system very well.3. Based on the empirical mode decomposition, the completeness and the orthogonality of the intrinsic mode functions (IMFs) were discussed briefly. For different IMFs, the energy distribution of gas/liquid two-phase flow was analyzed quantitatively, and the results uncover the relationship between the energy distribution and flow regime. The Hilbert-Huang transform was applied to the IMFs, and the time-frequency-energy (amplitude) three dimensional information distribution can be obtained and employed for further analysis. According to the experimental results, the marginal spectrum reveals the frequency-energy changes between flow regimes, the instantaneous energy reflects the accumulated energy distribution of each frequency in the whole time series, and the contour distribution of energy discloses the dominant frequency of the measurement.4. Wavelet package decomposition and information entropy were adopted to realize feature extraction for different flow regime, and the fuzzy cluster algorithm was exploited to realize flow regime classification. Based on the identification results, the dynamic characteristics of plug flow and slug flow were analyzed by multiresolution analysis and R/S method. The bifractal property was proved, and the quantitative and qualitative experimental results show that this phenomenon is caused by the discrete phase (gas phase in two-phase flow system). According to the results of R/S analysis, Hurst exponent and scale correlation were utilized to reveal the nonperiodic characteristic of gas/liquid two-phase flow, a modified P statistic analysis based cycle detection method was proposed, and the regularity of cycle time was calculated in order to conduct quantitative analysis for plug flow and slug flow.