CONSIDERATIONS IN THE PRACTICAL APPLICATION OF THE MULTI-SENSOR CONDUCTIVITY PROBE FOR TWO-PHASE FLOW

摘要

This study investigates two issues in the practical application of the local conductivity probe for two-phase flow measurements. First, the effects of signal "ghosting," an electrical interference inherent to multiplexing data acquisition systems, on the measured two-phase flow parameters are examined. A revised conductivity probe circuit is proposed to remove the effects of ghosting. The characteristics of signal ghosting are investigated experimentally with a specialized conductivity probe that enables concurrent acquisition of ghosted and un-ghosted signals within the same flow condition. It is demonstrated that ghosting causes higher bubble velocity and, consequently, lower interfacial area concentration measurements that depend on sampling frequency and sensor impedance. The revised circuit successfully eliminates this variability. Second, the sensitivity of measured two-phase flow parameters to increasing data acquisition sampling frequency is investigated experimentally. Measurements are acquired at incrementally increasing sampling frequencies with a four-sensor conductivity probe in 13 vertical-upward air-water two-phase flow conditions with superficial liquid and gas velocities ranging from 1.00-5.00m/s and 0.17-2.0m/s, respectively. It is found that the void fraction and average bubble velocity are insensitive to the sampling frequency, while the detected number of bubbles and interfacial area concentration can demonstrate a strong dependence. Considerations for selecting appropriate sampling frequencies in different flow conditions are discussed.