Averaged and time-dependent characteristics of the motion of an elongated bubble in a vertical pipe

Abstract

The motion of elongated (Taylor) bubbles in air±water vertical¯ow is studied by processing consecutive series of digitized video images. The shape of the elongated bubbles, as well as the velocities of the liquid±gas interfaces, are measured for various¯ow conditions. The bubble velocity variation caused by air expansion under the in¯uence of hydrostatic pressure gradient is measured and compared with model predictions. An oscillatory motion of the bubble bottom is observed. The frequency and the amplitude of these oscillations are studied as a function of bubble length and water¯ow rate. This information is essential for accurate modeling of developing gas±liquid slug¯ow. #

The relation between the Taylor bubble motion and the velocity field ahead of it

“…The digital image processing is employed for the measurements of the instantaneous and time-averaged parameters of the bubble moving along the pipe, such as its propagation velocity and shape, while the Particle Image Velocimetry (PIV) technique provides the¯ow ®eld in the liquid surrounding the bubble. A detailed description of the digital image processing algorithm is given in Polonsky et al (1999).…”

“…Tassin and Nikitopolous (1995), Lunde and Perkins (1995) and Donevski et al (1995) proposed methods based on video imaging and digital image processing for measuring shape, size and velocity of bubbles in a large volume of liquid. Polonsky et al (1999) applied this technique to obtain detailed quantitative data on the instantaneous characteristics of the bubble motion.…”

“…The averaged results for the bubble translational velocity are obtained for each liquid¯ow rate using a sequence of 100 to 200 recorded images of individual bubbles. The eect of the bubble length on U t was studied in Polonsky et al (1999) and was found to be relatively weak. This eect is attributed to the bubble expansion while rising along the unpressurized pipe.…”

“…The drift velocity U 0 can be determined from the measured translational velocity in stagnant liquid in the limit of short bubbles, where the eect of compressibility vanishes (see Polonsky et al, 1999). This value is found to be U 0 17X4 cm/s, corresponding to k 0X351.…”

“…8 summarizes the data on the variation of the maximum liquid velocity along the pipe axis as a function of the distance from the bubble tip, for dierent liquid velocities and for bubbles of similar length. The liquid velocity at the point x 0, which corresponds to that of the bubble interface, is equal to the translational velocity of the bubble nose as obtained from the bubble propagation velocity measurements (see Polonsky et al, 1999). The lines represent the best ®t of the experimental data.…”