Abstract
The mechanism of the transition from bubble flow to slug flow with co-current gas and liquid flowing through vertical tubes under rolling condition is studied. According to the experimental observation, it is found that the dispersed bubble flow pattern is periodically changed with the rolling motion. When the test section is deviated from the vertical condition, bubbles tend to flow at the upper part of the tube, and the bubble density reaches its maximum while test section rolling to the place with maximum incline angle. Besides, through the analysis of forces acted on moving bubbles under rolling condition, it is also found that the radial components of forces keeping dispersed bubbles at the upper part of the tube reach their maximums at maximum incline angle. Therefore, the transition from bubble flow to slug flow is most likely to take place at this moment. Based on the experimental data, a new correlation for predicting the transition from bubble flow to slug flow is proposed. The results show that the model predictions coincide well with the experimental data when gas superficial velocity is larger than 0.4 m/s.
