Local phase detection probes in fluid/fluid two-phase flows

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Abstract
Phase detection is of primary importance for both the control and the characterization of fluid/fluid two‐phase flows. Admitting that local probes ideally give access to the indicator function of one of the phases, various theoretical treatments of this information are reviewed. Optical, impedance, thermal and electrochemical techniques are then detailed, both for the associated theory of operation and the practical designs. A qualitative description of probe/interface interactions provides some insight into typical signal evolutions. From experiments performed in well‐controlled conditions, the relation between signal and hydrodynamic phenomena can be partially quantified. Additional difficulties encountered in realistic situations are presented. Usual signal processing techniques are analyzed, as well as calibration procedures. The resulting accuracy of the sensors is then discussed on the basis of volume fraction measurements. Suggestions are given for future improvements.