Single and double optical probes in air-water two-phase flows:: real time signal processing and sensor performance

To progress in the understanding of phase detector capabilities, a first requirement has been fulfilled by manufacturing reproducible sensors. A second objective, investigated in this paper, is to diminish the sensitivity of the processing technique to the various criteria required to perform the signal analysis. A new real-time signal processing technique, based on optical probe responses during probe-interface interactions, is presented, and its objectiveness is demonstrated. When used with mono-fiber or dual-fiber sensors, it provides local void fraction and gas velocity measurements. The performance of these measuring chains is evaluated in various air-water two-phase flows for different probes. Possible mechanisms responsible for void fraction uncertainties are discussed. It is also shown that monofiber probes with a conical-cylindrical-conical extremity are well suited to measure gas velocities in dispersed two-phase flows. (C) 1999 Elsevier Science Ltd. All rights reserved.