Various measurement tools of chaos theory were applied to analyze twophase pressure signals with the objective to identify and interpret flow pattern transitions for two-phase flows in a small, horizontal rectangular channel. These measurement tools included power spectral density function, autocorrelation function, pseudo-phase-plane trajectory, Lyapunov exponents, and fractal dimensions. It was demonstrated that the randomlike pressure fluctuations characteristic of two-phase flow in small rectangular channels are chaotic in nature.As such, they are governed by a high-order deterministic system. The correlation dimension is potentially a new approach for identification of certain two-phase flow patterns and transitions.
IntroductionThis study presents an application of chaos theory in identification of twophase flow patterns and transitions in a small, horizontal, rectangular channel. The data analyzed in this study is from previous experiments (Wambsganss et al., 1991; Wambsganss et al., 1992a and 1992b). In the experiments, horizontal two-phase flow was studied in a small cross-sectional-area (19.05 x 3.18 mm) rectangular channel. Adiabatic flows of aidwater mixtures were tested over a large mass flux 2 range (50 -2000 kg/m%). The full quality covered the range experimentally achievable. The two-phase flow patterns and transitions had been identified by dynamic pressure measurements, together with visual observations and supplemented with photographic data, and flow pattern maps were developed (Wambsganss et al., 1991; Warnbsganss et al., 1992a and 1992b).Usually, the flow pattern maps of two-phase flows are based on visual identification of phase distribution (Clarke and Blundelll989;Brauner and Maron, 1992;Galbiati and Andreini, 1992;Koizumi, 1992 and Hibiki et al., 1992). While visual flow pattern identification may be adequate for some cases, for many situations these methods are inapplicable or too subjective. Several other methods have been developed to more objectively identify and interpret flow pattern and transitions of two phase flow, such as pressure/time signals (Weisman et al., 1979), RMS of pressurehime series and friction pressure gradients (Wambsganss et al., 1991; Wambsganss et al., 1992a and 1992b), the power spectral density function (PSD), probability density function (PDF) (Hubbard and Dukler, 1966;Matsui, 1984 and1986;Tutu, 1982 andVince and Lahey, 1982). These studies have all contributed to understanding of flow patterns and transitions of two-phase flows, but there is no accepted method to objectively distinguish flow patterns.The purpose of this study is to apply the chaos theory on experimental data of dynamic pressure-to-time signals of two-phase flows in an attempt to identify and interpret flow pattern transitions. This new approach may present a promising way in identification of flow patterns.Chaotic oscillations are the emergence of randomlike motions from completely deterministic systems. Such motions had been known in fluid mechanics, but they have only recently ...