Measurement of wet steam flowrate using clamp on ultrasonic flowmeter

In order to measure steam flowrate at an existing pipe, clamp-on type ultrasonic flowmeter is suitable. However, the steam wetness increases with the heat loss, and the liquid film and the droplets may disturb the ultrasonic propagation for the flowmeter. In this study, ultrasonic propagation in a pipe was measured under air-water two-phase flow. Two ultrasonic sensors located at up- and down-stream positions were used for the measuring ultrasonic time-of-flight that depends on the flowrate. The signals were evaluated using cross-correlation values. Further, the same experiments were conducted at wet-steam facility. The results showed that the accuracy of the flowrate measurement strongly depended on the flow regime. In wavy flow, the time-difference of ultrasonic propagation were good agreement with the reference values, and the cross-correlation value was high. However, the measurement became difficult in annular mist flow. Thus, it can be said that the liquid film at inner pipe wall was significantly affect the ultrasonic propagation. (author)