The rise and deformation of a single bubble in ionic liquids

Ionic liquids constitute a new class of substances that are considered as potential substitutes for many traditional organic solvents in reaction and separation systems. But there is still a lack of transfer data due to the deficiency of research on the flow behavior. In this work, the motion and deformation of single bubbles rising in quiescent ionic liquids were investigated by injecting bubbles into three different ionic liquids ([bmim]BF4, [omim]BF4 and [bmim]PF6) through orifices with different inner diameters at various temperatures. Bubble size, aspect ratio and velocity were measured by processing images taken by high-speed camera, operated at 1000 frames per second with a resolution of 1280×512 pixels. The measured drag coefficient and aspect ratio were compared with correlations available in literature. The comparison showed that these correlations do not give fully satisfactory results in predicting the drag coefficient and aspect ratio of bubbles rising in ionic liquids, showing a big relative error. As a result, two new empirical correlations were proposed to correlate the drag coefficient as a function of Reynolds number and the aspect ratio as a function of a new dimensionless parameter IL which could group experimental data for gas bubble in ionic liquids. It was found that the values predicted by new empirical correlations are generally in good agreement with the experiment results.