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

Abstract

The flow around single Taylor bubbles rising in non-Newtonian solutions of Carboxymethylcellulose (CMC) polymer was studiedusing a simultaneous technique employing particle image velocimetry (PIV) and shadowgraphy. This technique solved previousproblems on finding the correct position of the bubble interface. Solutions of different polymer weight percentage, varying from0.1 to 1.0 wt% were used to cover a wide range of flow regimes. The rheological fluid properties and pipe dimension yieldedReynolds numbers between 4 and 254 and Deborah numbers between 0.012 and 0.402. The shape of the bubbles in the differentfluids was compared. The flow around the nose of the bubbles was found to be similar in all the studied conditions. Velocityprofiles in the liquid film around the bubble were measured. Different wake structures were found in the different solutionsstudied. With increasing viscosity, the wake flow varied from turbulent to laminar, being possible to observe a negative wake forthe higher polymer concentration solutions. A comparison between the different wake structures was made.