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Spectral Analysis of Line-Up Bubbles Flow Phenomena Using Electrical Impedance Signals in a Vertical Tube

The technique of spectral analysis for multiphase phenomena identification is based on the transformed in frequency domain of the electrical impedance signal. A sensor of variable size electrodes were used to measure electrical impedance signals caused by bubble trains in still water. The experiments have been performed in a vertical transparent pipe system. The spectral power density was correlated with observed phenomena through video recording, in order to show that low and middle frequency peaks can be associated to dynamic phenomena, while high frequency peaks could not be clearly correlated to flow particularities. Five characteristic range frequencies were identified: low-frequency large-amplitude and rising-energy, low-frequency middling-amplitude and rising-energy fluctuations, middle-frequency small-amplitude and decreasing-energy fluctuations, high-frequency small-amplitude and decreasing-energy fluctuations, high-frequency small-amplitude and constant energy fluctuation. Each frequency range was associated with the time domain and the individual peaks interpretation of the simultaneously observed phenomena by a video recording could be assessed.