クランプオン式超音波流量計による湿り蒸気計測のための透過波形評価手法

抄録

Clamp-on ultrasonic flowmeters are useful devices to measure flow rates in existing pipes. Many investigations have been carried out to measure steam flow rates using the ultrasonic flowmeters. However, the steam wetness increases with heat losses and the presence of liquid film and droplets may alter the propagation paths of the ultrasonic signals. Furthermore, signal-to-noise ratio decreases because the large acoustic impedance difference between the pipe material and fluid, strong signal attenuation in the fluid, and high temperature. Therefore, applicable conditions of the flowmeters are limited in the steam flow. In this study, the effects of liquid film and droplets on the characteristics of ultrasonic signal propagations in two-phase flows were investigated in adiabatic liquid-air two-phase and steam flows. Two ultrasonic transducers were used to measure the ultrasonic time-of-flight. Standard deviation was proposed to calculate the transit-time difference between upward and downward ultrasonic propagation. It is shown that the standard deviations of the target signals are more apparent than the averaged signals. Movement of liquid film inside the pipe wall is critical issues for increasing the noises. The standard deviation can be used to evaluating the setting suitability of the sensors.