On the streaming video of all typical flow pattern filmings on the experiment system by the high-speed video camera,the information of a single-frame was extracted and made into time-series.The series was analyzed with the non-linear chaotic recurrence plot(RP),less used in the last years.It was combined with the average diagonal length and Shannon entropy of recursive features changed after the increase of gas superficial velocity.The results showed that the information entropy of flow image combined with RP could well characterize the evaluated tract of gas-liquid two-phase flow patterns.At the same time,the information well characterized the volume fraction of all kinds of gas-liquid two-phase flow patterns.The average diagonal length and recursive Shannon entropy of recursive features all increased first and then decreased with the increase of gas superficial velocity,and it reflected the transition of the mechanisms of five typical flow patterns from the recursive characteristics.
Using the high-speed camera the time sequences of the classical flow patterns of horizontal gas-liquid pipe flow are recorded, from which the average gray-scale values of single-frame images are extracted. Thus obtained gray-scale time series is decomposed by the Empirical Mode Decomposition (EMD) method, the various scales of the signals are processed by Hurst exponent method, and then the dual-fractal characteristics are obtained. The scattered bubble and the bubble cluster theories are applied to the evolution analysis of two-phase flow patterns. At the same time the various signals are checked in the chaotic recursion chart by which the two typical characteristics (diagonal average length and Shannon entropy) are obtained. Resulting term of these properties, the dynamic characteristics of gas-liquid two-phase flow patterns are quantitatively analyzed. The results show that the evolution paths of gas-liquid two-phase flow patterns can be well characterized by the integrated analysis on the basis of the gray-scale time series of flowing images from EMD, Hurst exponents and Recurrence Plot (RP). In the middle frequency section (2nd, 3rd, 4th scales), three flow patterns decomposed by the EMD exhibit dual fractal characteristics which represent the dynamic features of bubble cluster, single bubble, slug bubble and scattered bubble. According to the change of diagonal average lengths and recursive Shannon entropy characteristic value, the structure deterministic of the slug flow is better than the other two patterns. After the decomposition by EMD the slug flow and the mist flow in the high frequency section have obvious peaks. Anyway, it is an effective way to understand and characterize the dynamic characteristics of two-phase flow patterns using the multi-scale non-linear analysis method based on image gray-scale fluctuation signals.
