(707c) Numerical Simulation of Single Bubble Rising in Ionic Liquids

Ionic liquids are now wildly used in industrial areas as new technological material. The fluid dynamic of these liquids is one of the most important aspects which are now interest and worthy of study. Predicting the motion of bubbles in dispersed flows is a key problem in fluid mechanics. In this paper, an improved VOF model was proposed and validated for simulation of single bubble rising in three different system, bmimBF4, bmimPF6, omimBF4. In the new model, we considered not only the surface tension proposed by Brackbill et al. , but also the drag force, which were produced between the two phases by a friction pressure drop. The comparison of the simulations with the experiments shows satisfactory. The terminal velocity of the bubble is some smaller than that of the experiment. The effect of bubble diameter on the rise velocity was not evident. Increase of the Eötvös number would increase the bubble velocity, with decreasing Eötvös number, the bubble gets its final diameter, and the equivalent diameter is larger than that of beginning. The velocity and the pressure fields around the bubble are presented (see Fig.1). At the top of the bubble, the liquid is pushed forward and fall around the bubble, there is no radial velocity along the axis far away from the bubble, and high downward liquid velocity is obtained near the bubble. The fluid flow in the region surrounding the bubble leads to a high pressure gradient at the bottom surface of the bubble. As the bubble rises, the upper surface receives a relatively steady flow resistance, which makes the deformation of the bubble. Acknowledgement: This work was supported by the National Natural Science Funds for Distinguished Young Scholar (No. 20625618).