Ultrasound measurement of large bubbles rising in angled slug pipe flows

This study details the problem of the ultrasonic detection of large bubbles rising rapidly in an upward gas–liquid two-phase pipe flow and proposes a new method to solve the problem. The proposed method uses two types of information, namely the echo intensity reflected by large bubbles and the Doppler frequency, which have different features in interface detection. The method using the Doppler frequency performs well in the detection of large bubbles regardless of the interface condition, whereas the method using the echo intensity has trouble in detecting an uneven interface. In contrast, the information of the echo intensity guarantees high accuracy of the interface detection even if that of the Doppler frequency has low accuracy for the detection owing to many small bubbles existing in the liquid film. Here, the two methods are combined to overcome their problems, and a validation test confirms that the results of the combined method agree well with the results of image processing. As demonstrations of the proposed method, the slug frequency, velocity, and airflow rate of large bubbles in an air-lift pump are obtained. The results confirm that the proposed method can be adopted for the high velocity of slug flow in various applications.