Ultrasonic pulse-echo technique for measuring instantaneous liquid level and time averaged void fraction in horizontal gas-liquid two phase flow

An ultrasonic pulse-echo instrumentation system was specially designed to measure instantaneously the location of a moving liquid-gas interface. Similar instrument had been demonstrated to be capable of measuring two-phase flow parameters for vertically injected gas flow systems. For the case of the horizontal pipe flow system, the instantaneous liquid level measurement was plotted against time, to characterize the different flow regimes developed, i.e., stratified smooth, stratified wavy, plug and slug flows. Since the contact type ultrasonic transducer was mounted from the outside wall of an aluminum pipe, this is yet the only available two-phase flow instrumentation technique, that is non-intrusive, which is capable of identifying the different flow regime patterns without having to construct a visible or transparent test section. The accumulation of 1024 instantaneous liquid level data points enabled us to measure the time-averaged liquid level and time-averaged void fractions for the different flow regimes. The results were compared with previous works, and for the case of stratified flow, the liquid hold-up measured was in agreement with Russel's et al model, and the void fraction measured was in agreement with Armand's correlation for the case of stratified smooth and wavy flows. The results as outlined for the various cases above, demonstrates that ultrasonic pulse-echo technique offers a feasible instrumentation alternative for two-phase flow applications. Digital schemes were employed to facilitate data recording and analysis by a microcomputer. The location of the water-air interface was determined to a maximum resolution of 0.075 mm. and to a maximum range of 307 mm. The sampling speed of the device is variable and its setting is only restricted to the round trip time-of-flight of the echo pulse from the transducer to the liquid-gas interface