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New Contactless Velocity Measurement Sensor for Bubble/Slug Flow in Small Scale Pipes

A new contactless velocity measurement sensor for bubble/slug flow in small scale pipes is developed with the contactless impedance detection (CID) technique. The new sensor consists of two same-designed CID modules (an upstream and a downstream) and an information processing module. In the upstream/downstream CID module, the capacitive reactance elimination principle is introduced to eliminate the adverse influence of coupling capacitances, and the analog phase sensitive demodulation (APSD) technique is adopted to obtain the fluid impedance signals (real part and imaginary part) of the gas-liquid two-phase flow. In the information processing module, the cross-correlation method is introduced to determine two initial bubble/slug velocities with real part and imaginary part of the fluid impedance, respectively. Then for each flow pattern, a velocity fusion model is established to fuse the two initial velocities. Based on the flow pattern identification result by a flow pattern classifier, the corresponding velocity fusion model is applied to determine the fused bubble/slug velocity. Three prototypes of the new sensor are developed and experiments are carried out. Experimental results show that the new sensor has good velocity measurement performance for bubble/slug flow in small scale pipes. For all the three prototypes, the maximum relative errors of velocity measurement are less than 3.0%. Results also indicate that the capacitive reactance elimination can successfully overcome the adverse influence of the coupling capacitances and taking full advantage of the total fluid impedance signals is an effective way to improve the velocity measurement accuracy.