Characteristics of echo signal of pulse ultrasound on boiling two-phase flow

Pulse ultrasound technique has been applied to measure the reflected echo signals from vapor bubbles in boiling two-phase flow. In this study, an ultrasonic transducer was developed for the ultrasonic measurement in boiling two-phase flow under the atmospheric pressure. Since the Curie point of piezoelements of the transducer is above 250 ̊C, it has an allowable temperature limit of 120 ̊C. The basic frequency of the ultrasonic transducer is 2 MHz and the ultrasonic beam diameter is 10 mm. The measured flow has rising vapor bubbles generated by the cartridge heater. The pulse ultrasound transmitted from an ultrasonic transducer travels into a vessel through the carbon steel wall of 1mm thickness. Echo signals are received by the same transducer. So the delay time and strength of a pulse echo are obtained from this measurement, and the distribution of vapor bubbles is obtained from reflected echo signals. Therefore the effect of boiling phenomena is estimated by the ultrasonic echo distribution.