In this work, a hybrid ultrasonic technique for diagnostic natural circulation gas-liquid two-phase flow is experimentally investigated. The method is applied on a two-phase natural circulation loop using a contrapropagating transmission flow rate measurement technique in the single phase section and a Doppler velocity measurement and single transducer pulse echo technique in the two-phase region. The two-phase natural circulation loop used in this work consists of a two-phase vertical section where the liquid has an induced flow rate by an air-lift pumping technique. Gas is injected into the lower region of the two-phase test section, and rises to a separation tank causing the liquid to circulate naturally about the loop. The liquid slug velocities, the air flow rates, and the liquid flow rates are measured, respectively, in the two-phase and single-phase section of the loop as well as two-phase interfaces and time averaged void fraction. A comparison with available results from other investigators is given, in terms of liquid superficial velocity and bubble velocity for two flow patterns generated in the loop; bubbly flow and slug flow. The results show that the present hybrid system can be used to identify not only flow regime but also key two-phase flow parameters for natural circulation conditions.

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