Flow in the annular film around a Taylor bubble rising through vertical columns of liquid

The flow in the annular film around individual Taylor bubbles rising trough stagnant and co-current vertical columns ofliquid was studied employing simultaneously particle image velocimetry (PIV) and pulsed shadowgraphy (PST). Thiscombined allows the simultaneous determination of the bubble interface position and the velocity profiles in the liquid film.Experiments were performed with aqueous glycerol solutions in a wide range of viscosities (2x10-3 Pa.s < µ < 0.22 Pa.s), inan acrylic column of 32 mm I.D.The results show that from the nose, the liquid film accelerates and below a certain distance stabilises in velocity and inthickness, becoming a free falling film. Values for the developing length and for the film thickness are reported for theexperimental studied conditions. Average velocity profiles in the fully developed region are also presented. A criticalReynolds number (based on the mean absolute velocity in the liquid film) around 400 is reported for the transition fromlaminar to turbulent regime