Gas volume estimation in a vertical pipe flow considering the bubble size obtained from an ultrasonic velocity vector profiler

A traditional ultrasonic velocity profiler (UVP) containing one emitter and receiver measures a single velocity component, which is laid on the ultrasonic beam direction; therefore, it cannot exact the motion of rising bubbles moving three-dimensionally in a gas–liquid two-phase pipe flow. In the UVP measurement, a small increase or decrease in the velocity causes a large error in the bubble size. This error affects the gas-volume estimation because the gas-volume measurement uses information on the bubble size obtained from the UVP. To measure the rising velocity of bubbles from a UVP installed on the outside wall of the pipe, the UVP should provide two-dimensional velocity vector components at least. To address these issues, we adopted a vector-UVP composed of one emitter and two receivers. Our UVP was tested on the existing method for the bubble size estimation using rising bubbles in a water tank. In the method, first, the bubble surface is detected using high echo intensities caused by gas–liquid surface. Then, the size of bubbles was estimated from averaging the rising velocity of the surface and the shape of the bubble surface. It is confirmed that our method provided just 1% underestimated velocity and 12% overestimated size compared with that of the optical visualization. Finally, we tried to estimate the gas-volume measurements in the rising bubbles using a vertical pipe and confirmed that the measurement error is approximately 30%.