Measurement of Liquid Film Thickness in Vertical Multiphase Slug and Churn Flows Using Distributed Ultrasonic Method

A distributed ultrasonic method for measuring the liquid film thickness of vertical multiphase slug flow and churn flow widely existed in industrial production is proposed in this paper. First, according to the proportional relationship between transit time of ultrasonic echo and liquid film thickness, we use the twin-crystal ultrasonic probe to measure the local thickness of liquid film. In view of the non-uniform circumferential distribution of the liquid film, three ultrasonic probes are installed on the same pipe section to measure the circumferential distribution of liquid film thickness. Then, a high-speed data acquisition system suitable for multi-channel and a data transmission system based on gigabit network are designed. The experiments of gas-liquid two-phase flow and oil-gas-water three-phase are carried out in a vertical pipe with a diameter of 20 mm. The fluctuation of local liquid film thickness has been measured by the distributed ultrasonic sensor, and the average thickness of liquid film of slug flow and churn flow under different flow conditions is obtained. The result indicates that the average liquid film thickness of slug flow and churn flow gradually thickens with the increase of liquid superficial velocity, and the distributed ultrasonic sensor can accurately measure the change of film thickness.