Abstract
This study reports the results of the characterization of an air-water two-phase experimental apparatus and the preliminary analyses of the experimental time series. The test section of the apparatus consists of a vertical pipe equipped with an impedance void fraction sensor. The carrying frequency of the impedance sensor has been chosen in order to operate it as a resistive sensor. The calibration of the sensor has been performed through comparison of the instantaneous two-phase mixture conductivity signal and the local actual dimension of the bubble as estimated from high resolution photograph. The calibration curve allows, therefore, reliable estimation of the void fraction time series. A preliminary analysis of the time series has been performed both in time and frequency domains, evaluating also the time series autocorrelation. These analyses have pointed out the inadequacy of linear tools for the characterization of two-phase flow dynamics, which are nonetheless characterized by strong recurrence and autocorrelation, which need to be further exploited by mean of nonlinear analysis in phase space. Phase space representation of different typical flow patterns, corresponding to a succession of bifurcation, shows the high potential of nonlinear analytical tools, to be adopted in order to exploit the system dynamics.
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