Flow around individual Taylor bubbles rising in stagnant CMC solutions: PIV measurements

The flow around single Taylor bubbles rising in non-Newtonian solutions of Carboxymethylcellulose (CMC) polymer was studied using simultaneously particle image velocimetry (PIV) and shadowgraphy. This technique made it possible to determine the correct position of the bubble interface. Solutions of polymer with weight percentage varying from 0.1 to 1.0 wt% were used to cover a wide range of flow regimes. The rheological fluid properties and pipe dimension yielded Reynolds numbers between 4 and 714 and Deborah numbers for the higher concentration solutions between 0.001 and 0.236. The shape of the bubbles rising in the different solutions was compared. The flow around the nose of the bubbles was found to be similar in all the studied conditions. Velocity profiles in the liquid film around the bubble were measured and different wake structures were found. With increasing solution viscosity, the wake flow pattern varied from turbulent to laminar, and a negative wake was observed for the higher polymer concentration solutions.